Part 11 - - Offline - 04-90

Part 11 - - Offline - 04-90
Electric Motor Test and Repaj,L
by: Jack Beater
Published by:
TAB Books
Montery Avenue
Blue Ridge Summit, PA 17214
META Publications
P.O. Box 128
Marblemount, WA 98267
permission of TAB Books.
Reproduction of this microfiche document in any
form is subject to the same restrictions as those
of the original document.
by Jack
A guide to maintenance
small horsepower
PA. 17214-
@ 1966 by TAB BOOKS
Printed in the United States
of America
or publication of the content in any manner, without express permission,
is prohibited.
No patent liability is assumed with
respectto the useof information contained herein.
Library of Congress
Book No. &6306-6097-6
Card Number: 66-24043
While many of
the larger
it more expedient
to replace
low horsepower
the rewinding
of small electric
a widespread
and profitable
is a distinct
a practical
guideA quick review
of the Table
book on the subject.
of Contents
that thisisthe
is not a college
theory -ridden
It is a workshop handbook,
every motor repair
will appreciIt contains
a wealth
on testing
and rewinding
small horsepower
of every type.
The Publishers
Table of Contents
Chapter 1
A Practical Motor Test Panel
Chapter 2
Tools for the Motor Rewinding Shop
Chapter 3
Time-Saving Coil Winding Machine
Chapter 4
Armature Testing
Chapter 5
Equipment for Testing Stators
Chapter 6
General Classification of A,C Motors
Chapter 7
Split-Loop Armature Winding
Chapter 8
loop Windings for Small Armatures
Chapter 9
Rewinding Fan Motors
Chapter 10 Rewinding Automotive Armatures
Chapter 1 I Rewinding Small Polyphare Motors
Chapter 12 Capacitor Motors
Chapter 13 Reversing Rotation of .Motors
Chapter 14 Brush Troubles and Their Remedies
Chapter I5 Varnishes for Rlectrical Work
A Practical Motor Test Panel
MOTOR test bench is almost a necessity for
the shop doing even a very moderate amount
of motor rebuilding or repairing. Even aside
from its utility value, which it certainly has, it is a
good investment from an advertising angle. The average customer coming into the shop will in all probability not know what this and that gadget is for, but
you can trust him to look around and note that you
use more than a hammer and a pair of pliers to install
a bearing or wind an armature.
The word of mouth advertising of satisfied customers is at once the best and cheapest kind of advertising for the service shop. For this reason many shops
having better than average equipment find that it
pays to invite customers back into the shop and to
spend a few minutes explaining some of the operations, and pointing out some of the special equipment
necessary to do a good job.
This is the kind of advertising most needed by
service men and service shops and it is the kind of
advertising that can not be bought with any sum of
money. A few satisfied customers can do more for a
shop than hundreds of dollars in advertising.
A good motor test bench is as essential in a motor
shop as a lathe is in a machine shop, and the up-todate motor shop should have both. The test bench
described in this article is in daily use in the motor
of an electric service* organization
where it paid for its cost in increased volume of
business within two months. This test bench is
not an expensive, elaborate affair, but is a practical outfit designed by a service man for use in his
own shop, and with one eye kept on the cost. Certain additions and refinements to the test bench
shown in the photo would undoubtedly be in order
for laboratory
or experimental
work, but for ev-
Fig. 1. Wiring diagram of complete test panel
eryday use in the small shop there is but little
room for improvement.
Figure 1 shows a wiring diagram of the motor bench
test panel suspended from the ceiling above. BY suspending the panel the surface of the bench is free
from. uprights, and motors can be pushed back and
forth along the top of the bench without hindrance
of obstructions.
The feed wires enter the test panel
through the conduit from above.
The bench is over 15 feet long and is used
for repairing motors and winding stators as well as
for testing. Only one section of the bench is reserved
for actual testing, a section about 4 feet long near
the center. Small and medium sized motors are serviced on this bench without having to be carried from
place to place for different operations.
The meters used ‘on the panel consist of an a-c voltmeter, an .a-c ammeter and a wattmeter. In making
up such a panel it may be possible to use such meters
as are already available in the shop. However, if only
one set are on hand it would probably be better to
keep them for outside testing and purchase a new set
of identical design for the panel board. New meters
of the proper ranges for this work need not be too
expensive. Satisfactory instruments for shop testing
of this nature can be had for about $8 or $10 each.
The seven switches used on the test panel described
here can be of any type, just so they make a neat aPpearance and have ample capacity for the work. Most
electric shops have on hand an assortment of switches
salvaged from old work or discarded switchboards,
and there should be little expense from this angle.
The buzzer for circuit testing is an automobile generator cutout or relay. 110 volt a-c current, when Passed
through the shunt winding of the cutout, will give a
loud buzz. The connections for this are from the generator terminal of the cutout to a ground on the base
of the instrument. When used in this manner for lntermittent testing they will hold up for a long period.
The following tests can be secured from this test
outfit :
Voltage of shop power lines, 110 volta and 220 volts,
single and three phase.
Line voltage with motor under test in operation.
Ampere reading with motor running or stalled.
Torque or brake horsepower tests.
Circuit or continuity tests, by test light or buzzer.
Voltage drops on any part of a circuit.
Ampere readings on any individual circuit.
Power consumption in watts.
Figure 1 shows a detailed drawing of the layout
of the instrument panel. Obviously, this ean he
changed to suit the builder’s particular requirements
but it will be difficult to obtain a more symmetrical
arrangement than that shown. Switch No. 1 is the
voltmeter switch, a double-pole double-throw type. In
the upper position, it connects the voltmeter with the
voltmeter test leads only, and the voltmeter is then
available for various tests independent of other switchboard circuits. When in the down position the voltmeter switch connects the voltmeter across the 110
volt line where it can be used to check line voltage and
variations of the same when motors are being tested.
Line voltages on the 220 single and three phase circuits can be tested from the voltmeter test leads when
the voltmeter switch is on the “TEST” position.
Switch No. 2, a single pole double throw switch, is
, 110
I .
4 I
1 z
II --‘i
Fig. 2. Portion of test panel devoted to testing
motors and appliances. Switch No. 2 in “up”
places ammeter in line; “down” posit& cuts
out of the circuit
110 volt
used to shunt the ammeter in or out of the 110 volt
circuit. When the switch blade is in the lower position current is by-passed direct to the motor under test
so that in case of serious trouble in the motor under
test the ammeter will not be damaged. Motors brought
into the shop for repairs, or those not known to be free
of shorts should always be tested with the ammeter
OUT of the circuit the first time. Throwing this switch
UP-when switch No. 4 is in the right position-places
the ammeter in series with the 110 volt line.
Switch No. 4 is the ammeter switch. It-is double
pole, double throw, and when in the lower position
places the ammeter in series with the 110 volt line
as mentioned above. This switch, when in the upper
position, connects~ the ammeter to the ammeter test
leads so that various readings can be taken. By placing these leads in series with one leg of the 220 single
phase line, or any one of the three phase leads, an
amperage reading can be obtained on 220 volt motors.
Switch No. 3, a single pole, double throw knife
switch, is used only with the continuity tests. In the
down position this switch connects the buzzer in se10
ries with the test prods, while in the up position the
panel light is brought into use. This testing circuit
is connected permanently to the 110’ volt line. The
test leads from this circuit, like those from the voltmeter, ammeter and motor switches are fastened to
the panel on the inside and cannot be removed. Hence
there is no time wasted in hunting for loose test leads
that have become lost, strayed or stolen.
Switch No. 5 makes or breaks the circuit to any
110 volt motor undergoing test. Switch No. 6 does
the same for the 220 volt single phase line, while
Switch No. 7 handles the 220 volt, three phase motor
leads. A three pole single throw switch can be used
here, but one two pole and one single pole switch
placed aide by side will make for hs.ndier testing. The
reason for this is that the one single pole switch offers an easy means of inserting the ammeter into any
one of the three phases for testing purposes.
When using the 220 three phase for operating a
motor the single switch can be closed first, and the
double pole switch will then control the motor the
same as though it were a three pole switch. In other
words, connecting but one phase to the motor will allow no current to flow, and a circuit can only be made
when the second, or two pole, switch is closed. We
can, then, clip the ammeter leads ‘to the upper and
lower contacts of this single pole knife switch on the
face of the panel, leaving the knife open. Then when
the two pole switch is closed we will get a reading of
the amperes in the motor phase connected to the single
pole switch. To obtain readings of the other two
phases we have merely to switch the test board leads
where they join the motor leads so that first one of
them and then the other is connected through the single
pole switch and hence through the ammeter.
The watt meter shown at the top of the panel is not
connected with any circuit on the hoard. This instrument has independent leads and clips so that it can be
placed in series with a motor under test. The duplex receptacle on the panel is wired to the 110 volt
circuit and is used for plugging in small motors, fans
and the like that are provided plug connections.
- -__---~.~
Fig. 3. Portion of panel used for testing 220 volt single
phase motors. The voltmeter and ammeter can be used
with this circuit for testing by making proper connections at motor terminals
The circuits shown on the test panel can be fused
or not as desired. In the case of the particular panel
mentioned in this article no fuse blocks are provided,
as the fuse cabinet of the shop entrance is but a few
steps away and should provide ample protection. Rowever, it would do no harm to fuse the test bench on
the reverse side of the panel.
To make the operation of the various tests clearer,
several drawings are shown in which the individual
circuits of the test panel are shown without the other
parts of the test outfit. Figure 2 shows the 110 volt
circuit; Figure 3 shows the 220 volt single phase circuit, and Figure 4 gives the diagram on the 220 volt
three phase circuit. The complete circuit for the test
lamp and test buzzer is indicated in Figure 5.
The foregoing covers the electrical testing of motors but the testing for mechanical efficiency is equally, if not more important. Hence the test bench must
be equipped with some device for measuring both the
starting torque and the full load torque of motors.
There are several methods, simple in application, that
are often used by the small shop to obtain these read12
Fig. 4. Diagram of the 220 volt three phase circuit on
nel. Voltmeter and ammeter can be
the test bench
connected in or c tween phases for testing motors under
running conditions
ings. Figure 6 shows the setup .for torque tests.
The drawing indicated as 6-A gives the details of
the Prony Brake test. In the past, at least, this has
been the most popular method of determining the
power of motors. It requires the use of a pulley, brake
arm and some form of spring or balance scale, one
provided with small enough calibrations to secure
readings on very small motors. The scale should, of
course, be accurate within reasonable limits.
The brake arm used with this test should measure
exactly 12 inches between the center of the pulley
position and the end of the arm where the load is
measured. The readings will then be in pounds-feet
directly from the scale. The brake arm is made in
the form of a clamp at the pulley end, and provided
wlth thumb screws so the tension can be regulated at
will. Hard maple makes a good material for the arm.
but when it is not available some other material lined
with brake lining at the pulley surface can be used.
For the most accurate results the brake arm should
be counterbalanced at the short end. Fairly stiff compression springs around the through bolts, and be13
tween the two sections of the arm, will make for mote
critical adjustments.
Before starting to make tests first be sure of the
rotation of the motor, or some sort of serious damage
may result. The rotation of the motor should, of
course, either push down on a platform scale or pull
down on a spring scale. In order to measure starting
torque clamp the arm to the motor pulley so that the
motor turns very slowly and read the scale.
To measure the pull-in torque release the thumb
nuts on the clamp until the motor is just able to throw
out the brushes in a repulsion-induction motor, or to
cut out the starting winding in a split phase motor,
and pull up to speed. The reading should be secured
at the moment when the brushes leave the commutator,
or in the case of a split phase motor, when the
centrifugal switch clicks out. The true pull-in torque
is the highest scale reading for which the brushes
will throw off and stay off the commutator.
The second method of testing motor torque utilizes
a rope and spring scale. The scale is suspended from
the ceiling and the cord or rope is attached to the
hook. This cord, incidently, should be small in diam-
fig. 5. Diagram of continuity test circuit.
Either the
Damp or buzzer can be used for testing by means of the
double throw switch
Fig. 6. Shop methods of measuring starting and full
load torque on small motors. In method “A”, tighten
thumb nuk until motor turns slowly, then take reading
from scale. In “B”, pull on rope untrl motor turns slow:; m;d s:rJe, and compute starting torque according
C”, add sand to bucket untd motor turns
slowly and takes up slack in rope at A. Weigh bucket
and sand to find pounds, then calculate starting torque
according to formula
. ’ .
eter and tough, such as a woven linen line about l/8
inch in diameter. The cord is wrapped around a flat,
flanged pulley on the motor shaft and the other end is
held in the hand. By pulling on the cord a load is
applied to the motor and readings can be had from
the scale. In some cases it will be necessary to bolt
or clamp the motor to the bench to hold it in place
while making the tests. Figure 6-B shows the arrangement for making this test.
Diagram 6-C shows the rope and weight, test. This
method gives satisfactory results without the use of
a brake arm or a spring scale. Like the test above it
does require a smooth flanged iron pulley of known
size. Tie a rope to a bracket at one side of the motor,
wrap the rope around the pulley a few times and attach a weight to the lower end of the rope. Oil or wax
the rope slightly to prevent grabbing. As the weight
must be adjusted to suit the power, or torque, of the
motor and some means of regulating the weight must
be provided. A simple way to do this is to use a bucket
partially filled with sand. Add or take away sand until the motor will just start. The bucket and the remaining sand can then be weighed.
Example. To test a s H. P. motor, 1725 R. P. hf.,
using a 4 inch pulley and a 118 inch diameter rope,
figure according to the following formula:
s,Jlr ,nn _PulkY dir lo hChU + mp di.. in indtu-4 + .I26 t,
12 I 2
4.126I w
st,rung torque in Lb. Ft. = Brake am Y. lvt. h”“P 00 Iup = T
Sluti~ torque
tarp”” In pm+nt Of * L. torque =F”,,,,,;,y,--
F”,, ,Md mQ”I in Lb. Ft. st,rt,*
,,e Lb, h,
C&ion must be exercised by the service man in
making these tests or bodily injury may result. Until
the operator is thoroughly familiar with the making of
torque tests he should be on the alert for flying
weights, spinning cords, lashing brake arms and motors jumping off the bench.
Tools for the
S IN any other trade the right tools play an important part in the success of a rewinder or
motor repair man. Men long in the business
have developed special tools for certain operations, and
have acquired others by purchase. To turn out work
at a profit-requires
the use of laborsaving equipment and production methods. The need
for special tools in the small motor shop is as great
as it is in the factory, although the kind of tools needed
for the motor shop will be simpler and less expensive
than those needed in the process of manufacture.
We have all known mechanics who seem to take pride
in the fact that they can get by with only a screw
driver, hammer and pliers. And “get by” is about all
they can do. The late Thomas Edison is once said to
have remarked to this effect: “It is surprising to see
what a good mechanic can do without tools, it is surprising to see what a poor mechanic can turn out with
the aid of good tools, but when you get a combination
Fig. 1. Detail of a simple hand-operated amatere winding machine
of a good mechanic and good tools-well, there’s no
limit to what he can do.”
The winder or motor repair man in the small shop
need not go without the necessary tools to do good
work and speed up his output. Many of the most necessary tools can be built right in the shop in spare time,
and the others can be purchased at reasonable cost.
Many a man starting in the business with little capitail has built up a good part of his tool equipment hiTself, and with tbe money earned from it has gone out
and bought more and better equipment as his business
The purpose of this article is to acquaint beginners
in the winding and motor repair business with a few
of the tools that are almost indispensable for the small
shop. These are in addition to other equipment, such
as testing outfits, armature and stator holders, winding benches, etc., that have been mentioned in previous
articles. Many of the items listed here can be bought
from jobbers or manufacturers of shop equipment,
such a course being recommended where possible. The
illustrations are typical of the kind of special tools that
have been found practical for the shop specializing in
the repair of the smaller types of motors.
Probably every winder has thought about the use of
an armature winding machine at some time or other.
Large electrically operated armature winding machines
are on the market, and are being used with success in
many a shop. They are practical and well worth their
cost where there is sufficient volume of business to
justify their use. Such machines, with a capacity of
over 100 armatures per day, would be out of placer in
the small shop where the daily avera,ge of rewind jobs
might be as low as two or three.
On the other hand, a simple hand-operated winding
machine is a very useful fixture for the small shop, and
also in the large shop for special work. One great advantage of the hand winding machine over plain hand
winding lies in speed. Another is the fact that, with
a suitable tension device, the coils can be wound ~with
an even tension and the turns accurately counted. The
latter is particularly important where the coils consist
of a very large number of turns.
Fig. 2. Wedge driving tool for pegging arma*~.-- .lLL.
rure PIOTS .
Figure 1 shows a diagram of a shop-constructed hand
winder. The base can be made from an old standard
of some sort, pipe, a large connecting rod from a discarded motor, or from wood. The shti-t and handle
can easily be made or salvaged from junk. The face
plate should be 1/” by 8”, either iron or steel, and
about 18” long. From each end a slot runs almost to
the center so that the armature shaft holding brackets can be adjusted to fit armatures of all lengths. The
armature to be wound is held in notches and fastened
with U clamps. By turning the machine around it can
be made to suit right or left handed operators. The
turn counter registers each revolution of the armature.
As indicated in the upper left hand corner of the illustration, strip insulation is best for use on this kind
of winding. Individual slot insulation can be used
but is likely to cause the operator a great deal of
trouble, as the wire has a tendency to catch on the corners of the paper. Strip insulation has another advantage in that it tends, because of the support from
adjoinmg slots, to remain in place while the slot is being filled instead of sliding out at one end.
In operation the wire is first looped over the star
collar on the upper end of the armature shaft, is then
fed into the first slot, around the drive end of the
shaft to the other side of its span, and so. on until the
full quota of turns has been placed. The end of the
wire is now looped over another notch in the star col19
Fig. 3. Cutting and gauging board for trimming
slot insulation
lar and the second coil is wound. This is repeated until all coils have been wound. At the completion of the
winding it will be found that all commutator leads are
over the star collar under tension and of ample length..
The wedging should be done before cutting the leads.
Bringing out the beginning ends of the lower coils on
top can be done by cutting the wire and placing as the
winding progresses.
As the wire is wound into the alots the tension is
regulated entirely automatically, the free hand being
used merely as a guide to see that the wire enters the
right slot. In making a tension device c8re should be
used to see that the enamel covering of the wire is not
cracked by bending too sharply. If a device similar to
the one shown in Figure 1 is used, the grooved wheels
over which the wire passes should not be of too small
Some rewinders use 8 brake ‘shoe with
spring adjustment that applies pressure directly on
the rim of the reel. The object of any device of thir
type is to maintain 8 constant and even tension at all
times, and to prevent backlash.
When winding armatures with more than one wire
in hand, additional tension devices will be needed, one
for each reel. The tension should be exactly the same
on all wires, otherwise the wire with the greater tension will tend to pinch and hind the sides of the looser
coil. When winding with more than one wire in hand,
the additional wires should have a tracer so that the
proper coil enas can be located without trouble. After
some practice the rewinder, with the aid of the hand
winding machine, should be able to double his output
over the straight hand winding method.
Another great aid to the winder is in the use of a
wedge driving tool. Many of the smaller, and some
of the larger, cores were designed for fibre wedges.
Fibre wedges, being flat, take up less space than do
the usual maple wedges, and as a consequence, it is
sometimes difficult to insert the wooden wedges over
a full winding in the space allowed. It is also true that
fibre wedges are brittle and tend to buckle and break
when driven without the aid of a tool. In very tight
spaces the wedge tool is a big help in driving home
wooden wedges also.
Figure 2 shows the details of a serviceable wedge
driver in cross-section and in use. Several sizes will
be needed to accommodate the various wedge sizes.
The body of the tool is made up on brass or steel strips
riveted together.
The sides of the tool should be
slightly thicker than the thickness of the wedges to be
Fig. 4. Metal drift for packing coils in slots
with narrow openings
used, while the top and bottom of the tool can be cut
from T/s” stock. Small steel pins, about l/16” in diameter, are used to rivet the parts together. After 8Ssembly the working end is ground down thin so that
it can be held close to the core without cutting or
chafing the winding. The plunger or driver should
be a free running fit in the slot and about ‘/2” longer
than the body of the tool. In using, a wedge is inserted in the slot of the tool and the tapered end of the
driver is held close to the slot entrance. A few light
hammer blows on the plunger head wiil force the wedge
into the slot without spreading, breaking or buckling.
Another great time saver for the rewinder is a cutting and gauging board for preparing the cell insulation for the slots. A board of the type shown in Figure
3 enables the winder to easily and accurately trim UP
a set of insulation to the desired size in a few momenta’ time. The adjustable gauge at the cutting end,
when once set to the right lengtb, allows the operator
to do the cutting at high speed without error. The
scale, marked off in inches across the top of the board,
makes for quick measurements
The foregoing cutting board can readily be adapted
as a machine for forming slot cell insulation to shape.
To do this a sheet of thin metal is folded once around
a section of the cutting knife, leaving the edge slightly
rounded instead of sharp. The slot paper is creased
Fig. 5. A device to aid in hand taping of armature and field coils
between this dulled portion of the blade and the edge
of the board. Only one crease can be made at a time,
but it can be made accurately and quickly.
Every winder knows how hard it is to pack down the
wires in slots having very narrow openings so that the
full quota of turns can be put in place. On slots having wide openings a square of fibre board can be used
to press down the wires, but on many armatures and
stators the slot openings are too narrow to make good
use of such a method. To overcome this difficulty it
will be worth the winder’s time to make up a set of
drifts such as the one pictured in Figure 4.
Drifts in the shape shown may be hard to obtain,
but the winder can have them milled from a solid bar
at any machine shop. To cut down on expense have
a twelve-inch length of l/s” cold rolled steel milled to
the indicated shape, leaving the shank a little less than
?/s”. Have the footing, or working edge, left about
:/s” thick. After the bar has been milled it can be
sawed into three 4” pieces, each piece being riveted or
bolted to a handle of some sort. The handle will make
it possible to use the drift inside small stators and a
good job can be done without the use of hammer or
After the three drifts have been supplied with suitable handles the foot, or working end, can he ground or
Fig. 6. Puller plate for removing commutators
and, at the left, a stand for using the puller
in a press .
Fig. 7. At the left is a puller for gears, V-pulleys and other small parts. At the right is a
puller for large leather, composition and steel
filed down to any desired width. For work on small
motors, )/a”, 6/16” and 3/8” will be the most useful
widths. By means of a small, fine file t.he edges and
corners should be slightly rounded and smoothed ‘so
that there will be no danger of damage to insulation
of wires or slot paper. A set of these drifts will save
a lot of time and make for a neater and more compact
Covering armature coils and field coils with insulating tape is a job that takes considerable time if done
with the bare hands. In the larger shops where there
is a considerable volume of this work a motor driven
coil taping machine is often used. Operating on the
same principle as the machines which wind the paper
wrappings on automobile tires, a coil taping machine
can make a lot of money for the shop if volume permits. However, there are few shops that have sufficient work of this kind to justify the outlay for a taping
Figure 6 pictures a device for use in the hand taping
of motor and generator coils. With this tool the taping
job is speeded up considerably as there is no time lost
in drawing through a long length of tape each time a
turn is made, or else in chasing over the floor after
a runaway roll that has escaped the winder’s hands. A
Fig. 8. At the left is a puller plate for removing inner ball races from shafts, while at
the right is a tool for removing outer ball races
from recessed holders
tape winder such as described will not work with coils
having a center opening of less than about 4”. for the
obvious reason that the tape winder wiii not go through
the hole.
Essentially. the tape winder is a means of holding a
roll of tape under the proper tension, so that as the
winder is rotated around a side of the coil it distributes the tape both evenly and firmly. After the first
turn or two the operator has only to fiip the winder
around the coil, handling it only once per revolution,
and seeing that as it progresses the right overlap is
made with each turn.
In making a winder such as is shown in the cut, the
two side pieces can be cut from thin sheet brass and
sawed or filed to shape. Four brass machine screws
hold the two sides the proper distance apart and also
act as guides for the tape. The roll of tape is centered
on a through bolt which, by the use of a wing nut, acts
as a tension regulator. Two thin fibre washers, sliihtly larger in diameter than a full roll of tape, are placed
one on each side of the roll for support. The overall
length should be kept as short as is possible for the
reason that this measurement is what determines the
minimum size of the coil which can be taped.
Another group of tools needed by the motor repairman consists of a set of pullers. No one type of pulier
is satisfactory fnr all purposes. Roughly. the puller
needs of the average small motor shop can be classed
as follows: Puller for small flat and V pulleys, puller
for large flat leather, steel or composition pulleys,
puller for small bronze bushings and a puller for commutators.
Figure 6 shows a puller plate for removing commutators from armature shafts.
The plate is in two
parts, held together by two wing bolts, and notched
in the center to fit closely to armature shafts. This
plate can be used in conjunction with several types of
pullers, and finds its best use in its aUility to pull commutators without subjecting the bars and insulation
to strains. The plate should contact the inner commutator sleeve and apply the pressure at that point
where it joins the shaft. On the left side of the figure is shown a wooden stand to be used with the puller
plate when the commutator is to he pressed off in a
screw press, or when it is necessary to remove the
commutator by hammer blows. The same plate can be
used to press commutators on the shaft.
Figure 7 shows two common types of pulley and gear
pullers. The one on the left is best suited to the
smaller types of pulleys and gears, and is well adapted
to removing V pulleys similar to those used on most
refrigeration motors. Pullers of this type can be had
that are self locking when under pressure. Note that
the puller jaws have projections which extend under
similar projections from the sides of the central nut.
It can readily be seen that as soon as the screw presses
against the nut, the nut in turn presses against the
jaw projections, thus forcing the jaws in toward the
work they are holding. The greater the force needed
to move pulley or gear the greater is the holding ability of the jaws.
The puller illustrated at the right is particularly
useful on the larger flat pulleys used on multi-horsepower motors. The jaws are adjustable for width by
sliding in the slot of the puller head, and they are adjuatable for length by making use of any of the not.ches provided in the sides of the jaws. The lips of the
jaws should be long enough to reach over t~he leather
or composition surfaces of built-up pulleys and to reach
the metal hub. The jaws on this type of puller can be
reversed, making the tool available for inside work,
such as pulling rings and working in recesses.
Figure 8 gives some details of a common type of
puller plate used in removing ball bearings of the threepiece type (magneto type). The plate, similar to that
shown in Figure 6, has a thin lip around the center
openingthat will clamp tight in the ball groove of the
inner race. This plate can he used in a press or with
a puller of conventional typle. A tooi for pulling outer
ball races is aIso shown. The construction of this
outer race puller is more complicated than is that of
the inner race puller. While such a tool could be turned
out by a good lathe man, it would probably be cheaper
in the long run to purchase such a tool from the
service tool list of some manufacturer. A tool of this
kind will only fit one size of bearing, hut adapters
for larger sizes can he turned out and used in connection with it.
There are many other tools that are equally handy
for the rewinder and motor repair man. Many of
these are made from old hacksaw blades, wood, fihre,
bits of brass or steei, and fashioned to suit the user
and to fit some particular job or operation. In fact,,
the good workman who takes pride in his job is al-,
ways making something, and sometimes the result of
an hour’s experimentation will result in a labor-saving
gadget that, in the course of time, will return big dividends for the time and effort spent on it.
A Time-Saving Coil Winding Machine
HIS business of repairing motors is rapidly
becoming specialized into two divisions. There
are those larger shops Cat service the needs
of the industrial field, and there are thousands of
smaller shops whose main source of business comes
from refrigeration
motors and other domestic and
commercial appliances. The larger organizat.ions
specializing in industrial motors have little intereat
in fractional horsepower motors because of the small
sum in dollars involved in such work. In fact, many of
the larger shops refuse to accept small single-phase
motors for repair.
The opposite is true of the small shop. They have
neither the skill nor the equipment to handle the large
work. They do a good job, however, with the fractional horsepower motors with only a reasonable
amount of equipment and a minimum of overhead.
And the number of these small motors is growing rapidly, affording prospects of increasing business for
years to come.
The profits to be made from the repairing or rewinding of sma!l motors is limited by severa: fac-
Fig. 1. Appearance of few pole stator projected on a plane surface. Note coil groups.
tors. Competition establishes the price that can be
charged. Two forms of competition face the small
motor shop. One form of competition comes from the
winding shops in the larger cities who handle such
work on a flat rate basis, the other comes from the
present low price of new motors. It ie obviously unreasonable to charge a customer $16 for a repair or rewinding job when a new motor of the same kind can
be purchased for a dollar or two more.
Recognizing this, some shops make it a rule never
to allow the repair costs to exceed 66% of the original
or replacement cost of the motor. If they can not see
their way clear to handle the job at this figure they
recommend the purchase of a new motor. Freight or
express charge8 should be included when figuring the
ratio of a repair job to the total cost of a new motor.
In exceptional cases, such as in emergency work,
the customer may be willing to pay even more than the
cost of a new motor if there is a considerable saving
in time.
Since the price that can be obtained for repairing
or rewinding small single-phase motors is more or less
standardized in each district, the profit available depends upon the ingenuity of each individual shop. The
shops that. are making money include not only those
most aggressive in obtaining business hut also those
who have developed methods of turning out the work
with the !ea;jt !abcr.
Since iahor is the moat expensive item entering
into the average motor job, the method of handling
the work will usually be the determining factor in the
profit or loss that results. The labor going into motor repairs can be conserved in two ways: by the use
of labor saving equipment to speed up the operations,
and by doing the work in odd and otherwise unprofitable hours. A combination of the two yields the
greatest margin of profit.
Let 1-m
I., I*Y..“.YI‘
n-=iAa- first the utilization of spare time.
Every shop will receive some motors that require complete rebinding.
The cost of supplying new stator
and rotor windings, commutator, bearings, brushes,
etc., will be approximately that of a new motor. In
such cases, the logical way to handle the matter is to
Fig. 2. This drawing shows a coil group
wound by hand. Unless spacing blocks are
used coils will rest on each other . . . .
minimum of expense. A representative stock of reconditioned motors, ready for immediate use, is one of
the best assets. from both a profit and advertising
point of view, that any motor service shop can have.
Quick and dependable service is one certain way of
retaining good customer relations, and this can be siccnmnli+ed
best by msin+aining an assorted .stock of
V...r.-“new and reconditioned motors.
The other method of reducing labor costs. the use
of time saving equipment, has been mentioned in this
series many times before. A large number of special
tools and jigs which simplify motor work have been
described from time to time. Although nearly every
tool and fixture required in motor work can be obtained from equipment manufacturers,
many small
motor service shops, limited in capital, firmd it necessary to either construct for tbemaelves such labor
saving tools as they require or else continue the use
of hand methods.
The coil winding machine, a tool that cuts hours into
fracticns when winding stators of the popular types
of refrigeration motors, is one of the most valuable
Fig. 3. Two views of a practical and easily
constructed coil group winding machine
labor saving devices. By the use of this machine, the
repairman can form a complete set of starting or running coils and have them ready for assembly in the
stator in only a few minutes. The tedious grind of
feeding the wire back and forth t,hrough the slots is
eliminated. The remaining operations consist of fitting the coils into the slots, inserting the wedges, and
making the connections.
For the assistance of those men who are new to the
business, we will describe the stator windings of the
two types of motors most generally used in connection
with electric refrigeration:
the repulsion-start,
induction-run motor, and the condenser or capacitor
motor. In the former there is but one winding on the
stator, the main or running winding, while on the condenser motor the stator field consists of two windings, the main or running winding and the starting
winding. In this respect the condenser motor is like
the split-phase motors which also have two windings.
In motors of these t.ypes, the section of the stator
laminations surrounded by one group of coils becomes
a pole. For example, if the total winding is wound
in the form of two groups, the motor is a two pole machine; if wound in four groups the motor becomes a
four-pole machine, and so on. All the coils that form
one pole of a motor are known as a pole .group. If we
cut a stator through on one side and roil it out flat,
with the windings still in place, it will appear as
shown in Figure 1. Here the pole groups are easily
identified, and we see that each pole group consists of
three, four, or more concentric coils. The first coil is
in the center of the group and each additional coil surrounds the smaller coils as shown in Figure 1.
Each pole group of coils is wound with a single continuous wire, the starting point being at the inside
coil. When winding by hand, the proper number of
turns are wound into the slots to be occupied by the
inner coil, then the wire is carried into the adjacent
slots on each side and the second coil is wound. The
wire is then carried to the slots adjacent to the second coil and the third coil is wound. This is repeated
until the full number of coils required in the group has
been completed, and the group ends with the wire coming from an outside slot. The proper polarity of each
coil group is determined by the direction of rotation
during the winding. The first group, for instance,
may be wound in a clockwise direction; the second
group should then be wound in an anti-clockwise direction; the third group, clockwise; the fourth, anticlockwise; and so on, according twothe number of poles.
In many cases, the hand winding of stators is tedious work because of the ,“spring” of the wire, the
smallness of the opening, sharp edges, or the difficulty
of maintaining the right tension at all times. The use
Fig. 4. The details of the molds used with
the winding machine of Fig. 3 are shown above
c rwu
Fig. 5. Typical diagram form of stator coil
pole group showing slot and turn data . .
of the winding “gun,” described in.a previous article,
is a great improvement over the straight hand winding, both in time saving and in the neatness of the
work. Only long experience and practice enables a
winder to turn out a neat, symmetrical job by the plain
hand method. Figure 2 shows the general appearance
of a coil group wound by either the hand or the “gun”
method. Note that in this type of winding, the coil
ends rest upon each other for support as the winding
progresses, and that there is consequently greater
chance for short-circuits between coils. Some rewinders make use of curved blocks between coils during the wind:‘ng to space the coils properly. The blocks
are removed, of course, after the winding is completed.
Xost factories, and many rewinders, use a method
of winding that has many advantages over straight
hand winding. This consists of the use of preformed
coils prepared by means of specially designed winding
machines. This method may be used to advantage in
rewinding motors of the type used in refrigerators.
Some poinis in favor of the prewound coils are: all
coil groups are alike as to size and shape; errors in
counting turns are practically eliminated; adequate
clearance may be provided between coil ends; and a
great reduction in winding time is possible. The elec33
trical resistance of coil groups wound in t,his manner
is practicaily always uniform.
A machine that will wind complete pole groups for
single-phase motors up to about 3 horsepower in capacity is easily constructed and will be a most useful
piece of equipment for the small motor shop. Almost
every shop has a junk box that will afford ample
material for the essenti,al parts and hold the const.ruetion cost down to a few dollars. The machine shown
in this article is typical only and may be simplified
or elaborated upon at will. The exact design will vary
with the materials available and the ingenuity of the
builder. For efficient operation, the features of electric motor drive, control clutch, and turn counter,
should be retained. Figure 3 shows two views of a
typical machine.
The machine can either be built on the end of an
ordinary work bench or it can be constructed as a complete unit. In either case, it is best to have the motor,
shafting, and belting below where they will be permanently out of the way. The base of the machine can
be made in any number of ways. An old arbor from
a belt driven grinder is one suggestion, but any substantial pair of bearings that will hold the shaft in
alignment will serve the purpose. The coil winding
jig bar is bolted to one end of the shaft; the drive pulley, to the other end. A pin or a sprocket to operate
the turn counter should be clamped on the shaft.
The power required to operate the machine is small
and may be obtained from a motor of about I/s hp. A
speed of about 30 to 60 turns per minute is all that is
desired. Provision for reducing the motor speed to
suit the work can be provided by the use of line shafting, pulleys, and belting. A clutch operated by a foot
pedal is a necessity and should be provided. If nothing better is available, a suitable clutch can be made
from wooden disks as shown in the illustration.
The molds upon which the coils are wound present
no problem if the shop is equipped with a lathe. Molds
to suit coils of any size can be turned out as required
and a representative assortment of forms will soon
be on hand to fit practically any type coil. These molds
should be turned from a block of bard wood, sanded
Fig. 6. Representative pole group taken from
winding machine. One advantage of this method of winding is the spacing between coils.
smooth, and shellaced. The details of a typical mold
and holder bar are shown in Figure 4.
The first step in winding a coil group is to measure
accurately the size of each coil forming the group.
This can best be done by salvaging one of the old coil
groups intact, or by winding carefully a single stiff
wire into the slots and forming it to the size and shape
desired for each of the coils in the group. With this as
a guide, the molds can be spaced properly on the bar
to form complete coils of the right size.
In winding a coil group, the beginning end of the
wire is tied to the spindle and brought into the groove
of the first coil through a small notch. Ample length
for connecting should be provided. When ready to
start winding, the counter is set at “0,” and the foot is
pressed on the clutch pedal. Either the largest coil can
be wound first, with the others in rotation, or the start
can be made with the smallest coil.
Let us suppose that the coil group we wish to wind
consists of 30 turns for the inner coil, 42 turns for the
second coil, 64 turns for the third coil, and 28 turns for
the iargest coil. On a winding chart this might be
shown as: 28/23-64-42-30-O-O-30-42-54-28/28. The
28/28 symbol denotes that the. side of the outer coils
of adjoining groups occupy the same slot. The -O-Oindicates that 2 slots in the center of t
are vacant. Figure 5 illustrates how this group would
be shown in diagram form,
In winding this coil, we start the machine and allow
28 turns to form in the largest groove of the m:Ad. WC
then stop the machine, readjust the counter to “0.”
and proceed to wind 54 turns in the next smaller
groove. Again the machine is stopped, the wire is
passed over to the next groove and 42 turns are wound.
We stop to pass the wire over and finish by winding
30 turns in the smallest groove. The coil group is now
complete, but before we remove it from the mold, we
should tie it to maintain its shape.
Short lengths of annealed wire make the best ties
for the completed coils. One turn around the coils on
each side is usually sufficient.
Care should be exercised so as not to injure the cotton covering or the
enamel. These ties are removed, one by one, as the
coil sides are fitted into their respective slots. Figure
6 shows the appearance of a completed coil group as
it comes from the machine.
The next step, that of assembling the formed coil
groups into the stator, is easy after a little practice.
Some patience is required when the slot openings are
narrow, but by pressing two or three wires into place
at a time the difficulty is overcome. If the slot lining
extends well above the stator bore, it will. guide the
coil sides into the slots. The proper polarity of each
coil group must be given consideraion as the coils are
assembled into the stator. The operations reqtiired
after the coils are assembled in the stator are the same
as in hand-wound jobs.
The use of a coil forming machine such as just described here will go a long way toward helping the
small shop to compete on an even basis with the larger
shops. In the face of aggressive competition, proper
equipment is essential. A machine similar to the one
mentioned here will do neat work, and what is probably just as important, will save hours of t~he motor
repair man’s time.
Armature Testin
ijCH has been written about the winding of
armatures but little about the methods of
checking up on the work as it progresses.
The winding of armatures is clean work and exceedingly interesting to those who like it until some form
of trouble turns up. Nothing can ruin the day for
an armature winder like a “bug” in the winding; one
t.hat stubbornly resists all efforts to locate it. Because
he has been so close to the work, the winder himself
may have difficulty in finding his own mistake; a mistake that msg be obvious to a fellow workman. In the
larger slzo~s, the foreman, or another winder, may be
called upon to do the trouble shooting, but the winder
who works alone must depend on testing methods to
insure accurate results.
In the usual course of winding, the winder goes
about the task more or less automatically, having de-
Fig. 1. A quick method of testing commutators for grounds is shown here. The wire connects all segments electrically so that only one
test is required
Fig. 2. This handy rack facilitates the testing*
of commutators for shorts between bars.
Springs in the hollow plungers, insure good
electrical contact with bars
veloped a certain familiarity with the work. Ever so
often, however, an odd job will turn up; one that so
taxes the ability of the winder t~hat an error may result
from his confusion. The error may be a short or a
ground caused by trying to pack a large number of
turns into a small slot. It may result from making a
wrong connection or any number of other reasons.
Most of the writer’s troubles in this respect have come
about as a direct result of telephone call interruptions
or from the idle chatter of well meaning visitors.
Regardless of how careful the winder may be in his
work, difiieulties will occur which cannot always be
prevented. The next best thing, then, is to detect such
error-8 as aocm as possible after they occur; not after
the winding is all but completed. To do this the
winder must use a system, a methodical routine of
work and test, work and test. The worst troubles that
may occur in armature winding are easily corrected
if diecovered in ti~me. Each coil that is wound over a
defective one makes the trouble shooting that much
more complicated and the remedy more difficult.
In armature winding, the most frequent causes *f
trouble can be traced to the following defects: short
circuits, grounds, reversed connections, and open cir-
Short circuits are most common defects encountered. They may occur between the turns of a coil,
between two coil sides occupying the same slot, between coil ends where they lap over each other, between
coil leads, and between commutator bars. Open circuits
do not occur often. Grounds are also rather uncommon where good slot insulation and fibre end laminations are used. and where the winding is performed in
a careful manner.
Test Commutators First
The commutator can account for a !ot of the winder’s troubles if proper testing is not done in advance
As soon as the armature has
of the winding operation.
been stripped, the commutator should be tested for
grounds to the shaft and for shorts between bars. The
test for grounds can be made by brightening the commutator and wrapping a bare copper wire around it
three or four times so that contact will be made with
all bars. Test from commutator to shaft using a voltage much higher than the normal operating voltage of
the motor.
Small motor commutators of the 110-220 volt type
should be tested at about 1000 volts for at least 60
seconds. A flash test is not always reliable because a
little time is often required for the defect to she-w up.
Alternating current is best for testing and can be
stepped up to the voltage desired by means of a transformer. The commrtators of very small motors, such
as are used in sweepers, mixers, etc., are often unable
to stand this test bacause of the thinness of the insulation, but such small commutators should ba able to
withstand double their normal operating voltages. A
rule often followed in testing the commutators of
larger motors, ya hp or more, requires the application
of 1000 volts plus twice the normal operating voltage.
The commutator of a 1 hp, 220-volt motor would be
tested at a voltage of 1440 volta, according to this
general rule.
Figure 1 shows the method of testing commutators
for grounds. A transformer can be constructed in
the shop that will have taps for feesting voltages of
100 to 1500, or more, in steps of 100 voits. The money
arid effort spent in constructing a good variable vole
age transformer is well justified, and the ouffit can
be used for many other kinds of testing.
The commutator should be tested also for shorted
bars. In ordinary work, this can be done satisfactorily with a IlO-volt test lamp. The trouble most generally found consists of carbon deposits on the surface
of the mica slot insulation.
When such a condition
exists, the test current arcs across these places and
makes their detection a simple matter.
This test is
made easier by placing the armature in an armature
stand so that it can be turned freely. Mark one bar
as a starting point and apply the test points to each
pair of bars as the armature is turned slowly. If much
of this testing is required, the construction of a bar
to bar testing device, such as the one shown in Figure
Such a device not only saves time
2. will be justified.
but eliminates tbe chance of skipping a bar or two
during the test.
Most shorts between commutator bars can be cleared
up by cleaning the surface of the slot mica. An undercutting machine is best for this purpose, but the
point of a knife, or a specially ground section of hack
saw blade may be used. If the burned spot goes deep
into the mica, it must be dug out, and the hole that
results should be filled with some form of commutator
cement. If no commercial form of commutator ce-
Fig. 3. Loose bars may be found in commutators that have been overheated. Test commuta!ors mechanically before beginning the
wmding and avoid difficulty ioter
ment is available, a good substitute can be made by
mixing plaster of paris and shellac into thick paste.
Pack this into the pole and test again after it hardens.
Several mechanical tests should be applied to commutators before the rewinding of the armature is begun. The commutators on armatures that have been
burned in ovens should be given a rigid inspection for
loose bars. Loose bars in a commutator may not show
up even when the commutator is stripped or dressed
in the lathe, but they may become evident when “staking in” the coil leads. Gentle tapping with a light
hammer will cause loose bars to shift their position.
Figure 3 shows how bars may shift on both the horizontal and vertical type of commutators.
If there is any indication of looseness, the commutator should be repaired or replaced. Nothing can cause
more trouble than a poor commutator.
Some fractional horespower, single-phase motors now have commutators that are insulated between the bars with a
bakelite compound instead of mica. These bakelite.
strips frequently burn and chare when overheated and
can seldom be used again. A winding is no better
than its commutator and the wise winder ascertains
that the commutator is in first class condition before
starting t,he winding.
Testing Coils for Grounds
After the winding has been started, frequent tests
for grounds should be made on the completed coils.
Tests need not be made on each coil as it is finished
but should be made on each group of four or five coib
as soon as they are in place. In the case of the straight
loop winding, where a continuous wire is used from
start to finish, the teat for a ground is made by touching the test points to.the starting end and to ground.
When a ground is discovered, and the teat has been
made on each group of coils as they were wound, the
winder may assume that the ground is probably in
the last few coils wound. Occasionally, the tamping
down of an upper coil will result in a ground in a lower coil. The exact coil in which the fault lies may be
located by cutting the loops between coils, separating
the winding into sections. The section of the winding
containing the ground can then be separated into individual coils and the test points may be used to locate
Fig. 4.
A ground in a loo
winding may be
located by separating CEIf s into groups as
shown above. By a process of e!imination, the
faulty coil may be located
the faulty coil. Figure 4 shows a method of locating
a ground in a loop winding.
When thearmature is wound with two or more wires
in hand there will be free ends projecting from the
slots, and each coil may be tested at any time. It is a
wise pian to wind two or three coils and then test them
before proceeding with the work. The upper, or finishing leads, can be bent back over the core to get
them out of the way, and the test can be made from
ground to each of the projecting starting leads.
Many grounds show up only after the wedging operation. The pressure of inserting the wedge in a
tightly packed slot may result in a puncture of the
slot lining, especially, if no fibre end laminations or
heads have been used. For this reason, the winding
should be tested again for grounds after the wedging
operation and before any connections are made to the
commutator. This may sound like a lot of extra work
but it takes only a very few minutes and may save
hours of time and the vexation of having to do a large
part of the work over.
Nearly every winder has a pet system of his own of
connecting the coil leads to the commutator. Some
winders use one method on one type of armature, and
another method on another type. The leads must he
connected to certain commutator bars, of course, but
there are ways of handling them. Some winders con42
nect the starting leads of each coil as it is wound to
the commutator.
The principle
of this
method is that the winder has no trouble whatever in
his finishing
leads as they are the only
ones that remain unconnected
when the winding is
A disadvantage
of this method is the COVIf an error has been
ering up of starting windings.
e, it wfll be d icult to correct without unwinding.
ome winders
e a natural winding method ,that
s the starting leads at the bottom of the coil and
the finishing leads on top. The e is little opportunity
for error in this system but there is a greater chance
of trouble developing later, such as shorts and grounds.
It is mu& more difficult
to insulate leads properly
8x-e buried deep under the winding.
Other winders manage to bring out both the starting and the finleads of the coils in the top of the slots, even
though the coils to which they belong are wound in
the bottom of the slots.
This is done by leaving these
e5ds outside of the slot to which they belong until the
rest of the winding for that slot is in place.
leads, the starting end of one coil and the finishing end
of another, are then laid in the top of the slot.
The winder may have difficulty in recognizing start
inishing leads unless some sure method of
st lamp such as the one shown
One of the best systems of
is employed.
requires that the start and finishing
If the starting ends are
leads be of unequal length.
clipped just long enough to reach the right commutator bars, and if the finishing
leads are left at least
two inches longer, mistakes are not likely to occur.
When the winding consists of more than one wire in
hand, which is usually the case with this type of winding, colored tracer wire will simplify connecting
will save the time of testing each circuit.
ake Coil Tests efore Soldering
Tests for shorts, grounds, and reversed connections
should be made as soon as the leads are staken in the
slot, and before t,he leads are soldered.
Unsoldered leads can be changed easily if a wrong connection is discovered.
They can be raised if special
tests should be required.
All armatures
can not be
tested in the same way or with the same equipment.
They can be given a final test for grounds, however,
by applying the proper test voltage to commutator and
Armatures can be tested for short circuits in a numDirect current armatures
and some a-c
ber of ways.
can he tested quickly and accurately in an
armature growler.
Some of the a-c armatures
of the
type have cross connections between opposite commutator
bars, and can not
be tested properly
in a conventional
type growler.
There is a special form of external growler available,
however, that can be used with these armatures.
Short circuited coils in armatures
of the type that
can be tested in the regular growler may be found by
passing a hacksaw blade above the armature, while the
is revolved slowly in the growler field.
sticking or vibrating blade indicates the presence of a
short in the slot beneath.
that pass this
test may still have trouble in the form of an open circuit or in reversed connections.
One of the best methods o+
+L- for open circ.uit3
L +a
in a growler is by means of a small lamp connected to
two test prods.
A good lamp for this purpose is a
Mazda NO. 63, such as is commonly used in automobile
dash and tail lights.
As the armature
is slowly revolved in the growler, the two leads to the lamp are
placed on adjacent
bars at a position
where the lamp will light with the greatest brilliance.
After this position is once found, all bars are tested
in the same position.
The test points may be held
still while the armature
is turned.
Since the potential
between adjoining bars is usually low, there is no danger of burning out the lamp.
As a matter of fact, the
voltage that wiii
be induced in most armature
Poor contact bewill light the lamp rather dimly.
tween the leads and commutator
bars will cause the
light to burn dimly while an open circuit will give no
light at all. Equipment for making such tests is shown
in Fig. 5.
D-c motor and generator armatures
are often tested
inside their field frame if it is available. This test can
b-G made before the commutator is soldered if the commutator leads are bound sufficiently
tight to prevent
them from being thrown out of place.
For testing
purposes it is best to energize the armature and field
of either a motor or a generator
with a voltage that
A sensitive amwill just cause the armature to turn.
meter in series with the energy supply will indicate reversed coils, shorts,
open circuits
by fluctuations
of the ammeter pointer and by arcing at the brushes.
A compass will provide a reliable test for reverse
connected armature coils. Current is applied to well
separated points on the commutator as shown in Figure 6. A compass is then passed over the coil ends opposite the commutator
end and the readings observed.
A reversed coil will cause the compass point in a
direction reversed from that observed for the properly
connected coils.
On small armatures,
it may be necessary to test one coil at a time to get an accurate
This is accompiished by lifting the coil leads
from commutator
during the test, making certain
each pair of leads are connected properly.
Cross connected a-c armatures,
and o?,hers of the
type of motor, can be tested satisfactorily
by installing
the armature in the stator with the brushes removed.
With the bearings properly adjusted to allow no rubbing, connect the motor to an a-c circuit and turn the
armature by hand.
A clear winding will allow the rotor to be turned easily while a short circuit at any
be used to check
In the case of
essafy to lift
point in the armature winding: will cause the rotor to
As stated previously, the brushes
lock in one position.
must not touch the commutator during this test.
any short circuits, and a, few grounds, that are
found in rewound armatures,
are caused by the solderFor this reason, it is advisable to make
ing operation.
the main test after the commutator
been completed and before they have been soldered.
Xf trouble becomes apparent after the soidering job has
been accomplished the winder will know that the source
of the trouble is in the commutator,
and not in the
winding proper.
Shorts that appear in the commutator
after soldering can usually be traced to three things:
solder between commutator
bars, solder that has flowed below
the winding and shorted commutator
leads, and the
use of acid flux.
Small particles
of solder often
wedge in commutator
slots and complete an electrical
These wiil sometimes burn out in
path between bars.
the growler teat, but if not, they can be located by using
the method abown in Figure 6. Test from bar to bar
and the trouble will be located between bars that do
Surplus solder that has
not cause the lamp to light.
found its way below the winding and caused a short can
be located in the same manner. If an acid flux is used
in the soldering, the acid will sometimes soak
into the insulation and cause shorts or leaks. The pas46
sibility of this kind of trouble should be avoided by
using a rosin flux.
If the job is worth doing, it is worth doing right.
Frequent tests while the work is in progress will result in better work and will eliminate
the need for
patch work on mistakes made during the earlier stages
of the winding.
B1S articie describes the methods used in tesling the various types of stators for the many
iaults or defects that may occur during the rewinding operation.
The majority of jobs coming to
the small motor shop consist of the small singlephase motors, and many of the tests mentioned here
will seldom be used on that class of winding. However,
a certain percentage of the business will include other
types or’ motors and it is well to have the proper equipment and knowledge of testing methods available for
this out of the ordinary class of work.
The winder with some experience on the fractional
horsepower motors such a.s are used in refrigeration
soon arrives at the point where he needs to give but
little time or thought to testing his work. A ground
test and a check up on the polarity of his coils is usually
Practice makes for perfection and he seldom has trouble with this familiar type of work.
Different conditions may exist, however, when he
obtains an unusual job, a motor of a type which he
Doing a good winding
has perhaps never seen befor:.
job on simple single-phase motors is one thing; doing
a satisfactory job on a large polyphase motor is something else again.
The first may demand only a small
amount of mental alertness;
but the second will require that he keep his wits about him. There may he
but a slight chance for error in the first job, but there
are plenty of possibilities for mistakes on the latter.
And when a mistake is made, ;t is an advantage to
know reliable testing methods.
A rewound stator should be tested twice if possible;
first, by routine tests before the dipping and baking
and, afterwards, by giving the motor a test run. The
latter test will show up almost any defect, but because
of the lack of the proper power supply, absence of essential motor parts or other reasons, it is not always
ewound stator windings should be
o~o~~b test for grounds.
A lamp
test ~~~~owed by a magneto or high voltage
transporter test gives assurance of clear coils
possible to conduct the test run in ihe winding shop.
It is in such cases that the routine method of testing
proves most advantageous.
The first of the important routine tests comes just
after the winding has been connected. and at this point
the necessity of making an accurate diagram of the
connections of the original winding is fully realized.
Any winder who assumes a stator winding job on a
motor of a t.ype with which he is not thoroughly familiar stands to lose a lot of his time and waste a lot
of ycmd material unless an accurate and complete diaThe prepgram is prepared of the original winding.
aration of such a diagram may be considered as one
of the most important parts of the job.
After xhe stator has been wound and connected the
entire job should be rechecked against the diagram.
In some of ~i;ti larger shops this checking is done by
In any case, the check up
the foreman w head winder.
on the conneetionz should be done by some competent
person other than the original winder himself if this
is possible.
Given a correct diagram to start with
and a system&k inspec:ion, no errors in connections
should go beFond this step.
e smaller single-phase motors, testing rarely
includes more than checking for grounds and polarity.
Pn ~v~~~~~g the stators of two- aud three-phase mo49
Fig. 2. Short circuits in stator windings
e located easily with an internal growler.
gives construction details for a
-cycle, a-c growler
tors, however, several other factors must be given conStators for motors of this type should not
only be rigidly tested for grounds and polarity, but
they should be carefully tested for short circuits and
Detailed explanations of
for balance between phases.
these tests follow.
Grounds in stator windings may be located successfully by several methods, such as with a test lamp, with
a bell ringing magneto made for the purpose or with
Probably the best
a step-up testing transformer.
method is to combine the first with one of the others.
Figure I indicates this clearly.
The simple test lamp
~~~~e~t~~ to the light socket will indicate at once any
If the lamp test indicates that
low resistance ground.
the w~~di~~ is clear, it should then be subjected to a
more rigid test with a higher voltage.
The value of
this test voltage will depend upon a number of factors,
such as the working voltage of the motor, the type of
~a~~ati~~ used and the kind of service the motor will
called upon to render.
Motors operating in damp
or wet places and motors subject to high temperatures and continuous duty will need better insulation
than motors used intermittently
under more ideal conditions.
No simple rule can be given for determining
test voltage to be applied to stators, but in general it
from at least two to three times the value of the norAs mentioned before, the highal operating voltage.
er vortices for making these tests can be obtained
a step-up transformer
such as is used for armature testing, or from a hand operated magneto.
er method is more reliable since the voltage
applied in known values, while the magneto
varies with the speed at which the crank is
single phase stator for grounds, each
tested separately if the stator is one
type wound for use on 110-220 or other paired
es. The test is from one lead of a circuit to a
Since all three
the et&or frame.
se stator are internally connected
it is only n~eaaa~
to test from any one of the three
The same rule applies in testing
inale to ground.
a ~Q~~ase
stator of the three wire type, but in a
four-wire two-phase stator there are two independent
circuits and each must be tested individually.
After successf
passing the ground test the statar should be checked for short circuits in the winding. This is beat done by means of an internal growler, a piece of testing equipment that serves the same
purpose for a stator aa the regular growler does for
an armature.
Instead of moving the winding through
the growler field, as is done with an armature on a
pocket compass is useful in checking the poiarity of a phase winding. The test
must be made with a d-c voltage applied to
the winding
regular growler, the winding of the stator remains
and the internal growler is moved from
place to place.
Many service men have only a hazy idea of the working theory of the growler, and hence a brief description may be of some benefit.
Almost everyone who
has worked with electricity to any extent understands
the operation of a transformer.
We know that when
(or int.ermittent)
is passed
through a coil of wire wound around an iron core that
this eore becomes magnetized.
We also know that,
when a second coil is placed in the magnetic field thus
created, but electrically insulated from the first coil,
a voltage is induced in its winding which is directly
to the voltage in the first coil and the
ratio between the number of turns in the two coils.
The coil to which the voltage is supplied is referred
to aa the primary coil, and the coil in which the voltis induced is called the secondary coil.
The growlGrowlers operate on the same principle.
er proper consists of the core and a primary winding,
and the stator coils under test comprise the secondary.
Thus when the growler is in actual use it is nothing
To explain how a growler
more than a transformer.
indicates a short in the stator windings, we may conveniently refer to the action of a typical transformer
under different conditions.
If we take a suitable transformer
and connect the
primary winding to an a-c supply source, leaving the
secondary ternnnals
unconnected, we will find that
the flow of current through the primary
is almost
In this case the core becomes saturated
which tends to retard the flow of current in the primary winding except such as required
to establish the magnetic field. However, if we connect the secondary winding terminals to some form of
load we find. that there is an immediate increase in
the current drawn by the primary.
The current in
the primary winding will depend upon the current supplied from the secondary.
When the section of the
stator winding under the growler contains a short
circuited coil, the primary current reaches a maximum
On the other hand, when the internal growler
is held over stator coils that are free of shorts, there
is no circuit in the secondary, and the current in the
growler primary is a minimum.
These facts are used
to good advantage when testing for shorts.
Figure 2 gives the details for constructing
an internal growler suitable for stator testing on a wide variety of motor sizes. The preparation
of the laminated core is the only difficult part of the job and this
will be simplified if the core from an old transformer
of the right kind is available.
The core ohould
N shaped, with the coil wound in the center.
The bot53
This diagram shows the proper conmaking a polarity test on a threeconnected stator. The winding
unconnected at one point as shown.
tom legs of the core should be rounded so as to fit ne
inside bore of the stators. Laminations of a larger size
can be trimmed down to fit with a pair of tin shears.
The core should be firmly bolted or riveted together
A thumb
with provision for some form of a handle.
switch on the handle will greatly facilitate the use of
an internal growler.
With the aid of this growler, shorts can be detected
One method is to use a hacksaw blade
in several ways.
to “‘feel out” the winding one coil pitch in advance: of
If the blade tends to stick or
growler’s po-ition.
rate, the short will be located under the surface
Another method that gives very good
at that point.
reeults is to cut an a-c ammeter into the primary circuit of the growler. In a clear winding there will be
but little current flowing in the primary and the ammeter will give a low reading.
However, as soon as
the growler
is located over a coil containing a short
circuit, the current flow in the primary will increase.
The current indicated by the ammeter will depend
upon the reaietance of the short circuit.
Figure S
shows a circuit diagram of a short circuit testing device of this kind.
The internal growler hae still another use: it can
also be used for locating grounds.
The growler is
about inside the stator and at each position
one lead from each of the stator circuits is flashed
ee-phase winding is projected
ce here to show the results of
ty check obtained with a compass.
ses are indi~a~d as “a”, “b”, and “c.”
back and forth against the bare metal of the stator
eore. If a spark is produced from any of the leads it
indicates a ground in that circuit.
When an ammeter
is connected in the growler primary it will also indicate the presence of a ground under the same circumstances.
This method of testing for grounds is shown
in Figure 5.
Occasionally a mistake is made in connecting the
Such errors can be
stator coils in polyphase motors.
found easily with simple testing equipment and a little patience.
One method makes use of a polarity test
which requires a source of low voltage d-c current, an
ammeter, several lamps of the proper voltage and a
The testing current in amperes
small pocket compass.
should be about 5% of the full load rating of the motor through one phase of the stator winding. A 6-volt
auto battery wil supply ample current for all ordinary testing, and one or more 6-volt lamps in seriesparallel with the line will limit the flow to the desired
value. An ammeter in the circuit serves as a check
upon the current passing through the winding.
In testing a poyphase stator winding for polarity,
only one phase is tested at a time. The test leads are
connected to the terminals of the winding and the eomAs the
pass is passedaround
the inside of the stator.
compass passes the center of each “live” pole the
needle will be deflected toward the pole center and the
s will indicate whether the pole is a “north” or
a %outh.”
Poles giving a “north”
marked with crayon in the form of an arrow pointing
Fig. 8.
In testing a delta connected winding, each phase must be checked with the
current flowing in the same direction.
proper battery connections are shown above.
toward the operator.
Those giving a “south” indication are marked with an arrow pointing away from
the operator.
As soon as one phase has been tested
the test leads are moved to the next phase and the
Figure 4 shows
same test and markings are repeated.
a close-up of the method of testing and marking the
In testing a three-phase star connected winding, one
of the d-c test lines must be attached to the star point,
The other test
or center junction of the three phases.
lead is alternateiy connected to phase leads A, B and’C.
This is shown b:y the diagram in Figure 5. The test
connections for making a polarity check on a threephase delta connected stator are shown in Figure 6.
If the stator core couid be split and rolled out flat at
the end of the test :he markings would appear as those
shown in Figtire 7. It will be noted that all poles of
a phase alternate
north and south, as do adjoining
poles regardiess of their phase connection.
The compass method of checking the polarity of
s:ator windings is nearly fool proof except for having
the proper te*t line connections to the battery supplying the testing current.
If the battery lines are
switched it will change the compass readings. ‘Therefore all phases of a stator winding should always be
tested with the current flowing in the same direction.
An ammeter in the test circuit helps to keep a close
Fig. 8.
In testing a delta connected windase must be checked with the
current ~~ow~~g in the same direction.
proper battery connections are shown above.
check on p+zsiuie mistakes of this kind, as the meter
p;xding will be reversed if the leads are changed.
In testing a star connected winding for polarity.
place the negative baitery lead to the star point, and
use the positive iead to connec! to the three phase leads
in turn.
Thtre is a slight chance for a mistake if this
is done en thl.: type of connection, but with delta connected stators both battery leads must be changed for
each phase test and the chance for error is correspondBecause a delta cozlnected winding
ingly greater.
forms a closed circuit between any two phases in order
to obtain a correct test.
Figure X shuwj the method
of testing individual phases on a delta winding.
The last of the important tests to be mentioned here
is the phase-balance test.
The test consmts of measuring the fiow of current established by a known voltage and frequency through each of the phase windings
with an accurate ammeter.
The current established
in a!1 phases should be equal. The current used for
the test shouid be substantially
les- than the normal
operating current; about 25(~< of the normal rating
is sa:isfactury
but the frequency should be that for
which the motor is rated.
This adjustment in current
flow require-s the use of a transformer
of the proper
Figure 9 shvws the arrangement
of the circuit for
testing current flow by phases in a star connected
Fig. 9.
An important
test on every threephase stator is the phase balance test.
this test, a known voltage is applied to each
phase winding and the current measured
The ammeter, and preferably a voltmeter
also, is placed in the test circuit to obtain direct
As with the polarity test the star point
forms one testing point for all three phases while the
other test lead is connected to the three phase leads
in succession.
No diagram is shown for balance tesling a delta
connected stator winding but a study of Figure G will
indicate the proper method.
As with the polarity test,
the winding must be opened between two phases so
that the testing current will flow through only one
winding at a time.
If the balance test show that the
current flow is unequal in the different phases it is
an indication that there is an error in the winding or
in the connections.
Such errors may be of the nature
of reverse connected coils or groups, short circuits,
unequal number of coils in phases, open circuits, or
HE primary classification
of alternating
current motors consists of two divisions:
Singlephase and polyphase. These names are self explanatory
to those who have some knowledge
A single-phase
motor is one in
motor windings.
which the winding consists of a single set of coils, so
connected that they generate a single wave of alternating magnetomotive
A polypbase motor, on the other hand, has two or
more phase windings which are so distributed
or connected that two or more waves of alternating
magnetomotive farce, different
in phase, are produced at
the same time. Thus a two-phase motor has two
phase windings so distributed
around the field that
the result is two separate magnetomotive
force waves
which are 90 electrical degrees apart, the waves of
which are spaced 120 electrical
degrees apart.
mostly in the fractional
sires, the single-phase
motor has the widest use of
any electric motor. This comes about partly because
the majority of them are in service in homes, offices
and stores where the only source of current supply
comes from the lighting circuit. Single-phase
of various kinds are made in larger sizes to meet
special conditions,
but their use cannot be said to
be general.
Single-phase motors can be classified, according to
the principle of operation,
into five general typea:
Series, Capacitor
and Synchronous.
There are subdivisions
to some of these
types, and in some cases, overlapping
features. Each
type or characteristic
will be considered in order. It
should be noted here that single-phase motors of the
induction types are not inherently
needing some form of auxiliary winding to bring the
rotor up to speed.
The two most commonly used
_ cmethods of starting
fare by split-phase, and by repulsion.
.A. C
Fig. 1.
Diagram of straight
repulsion motor circuits
motors enjoy a
very limited use, and are not to be confused with the
more popular
more popularly
k,nown as “repulsion-induction.”
Straight repulsion motors employ a running winding
wound on the stator, and a wound rotor of conventional type. There is no electrical connection between
the Prmature winding and the stator winding.
Current is induced into the armature winding from the
action of the line supplied running winding. The brushes used in a motor of this type are
short circuited together, and placed in such a position as to cause the induced current of the armature
+o create the torque necessary
to run the motor.
WINDING e&s NO C;INNECT!ON co ?obvER suF”c*
0.2 :,4:;p+ ,*:yi’,x;z
sion motor
diagram of
anging the direction of rotation of these motors is
accomplished by moving the brushes to a point either
side of the neutral position.
See Fig. 1.
repulsion motors have been
which make use of a third winding,
and which are known as compensated
In addition to the running winding and the
winding on the armature
or rotor, there is another
winding incorporated
in the field ring and which is
to the commutator
of the armature
means of brushes. The compensating
winding has no
connection to the running winding or to the power
The object of the compensating
winding is
to reduce sparking at the brushes on the one hand
and to increase the power factor on the other. A schematic diagram of such a motor is shown in Fig. 2.
The repulsion-start,
motor is one of
the three leading types of fractional horse power motors in use, and its name comes as a result of its operating characteristics.
Like the straight
motor this type has a running winding and a wound
The winding on the rotor, or armature, however in this case, can be considered as an auxiliary
winding as it is used in starting only, and its sole
function is to supply the torque essential to bring the
motor up to the lower limits of a normal running
Fig. 3.
run motor
spu ;.on-sta:t,
a r-4
hen starting, a motor of this type operates as
straight repulsion motor. As soon as sufficient
is attained to cause the motor to produce the torque
needed to run as a straight induction motor, the armature windings
are short-circuited
the result that at normal speeds the rotor functions
the same as the squirrel-cage
rotor of a plain induction motor. The method of short-circuiting
the armature windings
in a repulsion-start,
motor is actuated
by centrifugal
weights, and on
many motors of this general type the same device
at shorts the commutator
segments also lifts the
brushes from the commutator.
This not only prevents useless wear on the brushes, but tends to reduce minor sparking caused by incomplete shorting
110 ‘4 LINE
Fig. 4.
of the armature windings and radio interference.
wiring diagram showing the connections
of a repulsion-start,
motor is shown in Fig. 3.
The split-phase motor is another popular type, the
use of which is generally confined to the operation
of small machinery where the starting torque is not
too high. A motor of this type employs two windings,
both wound on the stator, a main running winding,
and an auxiliary or starting winding.
The rotor is
of the solid, squirrel-cage
type. A simple centrifugal
switch disconnects
the starting
winding from the
line as soon as the speed necessary to operate as a
plain induction motor is reached.
The main winding of the split-phase motor is arranged in pole groups as is usually found in other
The starting
wound in coils above and between the main winding
coils, the reason being that these starting coils will
set up a rotating field a certain number of slots distant from the effect of the main coils, and cause the
rotor to revolve. ’ The starting winding is of no further use as soon as the rotor attains a normal running speed, hence the automatic switch cuts it from
the line, conserving current and preventing the high
winding from over heating and
burning out. Fig. 4 shows the circuits of a motor
of this type.
motors of the series types are more often called universal motors, in
as much as most of them are built to operate on a-c
or d-c current of like voltage.
In general these motors are of miniature size and find a rather wide use
in fans, carpet sweepers, drink mixers, juice extractors, sewing machine motors and for similar tasks
where the duty is intermittent
and first cost an important consideration.
Series motors have a field-usually
two pole-that
is wound like the coils in a straight d-c machine. The
is wound like a d-c armature
and is in
series with the field. Motors of this kind are finding
less favor than :formerly due to the fact that they
cause more or less interference
with radio reception.
The judicious
use of by-pass
condensers will, however, quiet most of these motors.
The simple circuit
diagram of the series motor is shown in Fig. 5.
The capacitor, or condenser motor, has moved rapidly to the front, especially in the field of electric refrigeration,
because of its greater power factor, efficiency and economy of operation, over other types of
As in the split-phase
the capacitor motor has two windings. The main, or
running winding, is conventional
in design and with
the motor in operation, is connected across the line.
The starting
winding is approximately
90 electrical
degrees from the main winding, and is connected at
one end to the line; while the other terminal ends on
one post of the running condenser.
The capacitor
motor has been designed in several ways, for experi64
Fig. 5.
iring diagram of a single-phase motor
of the series or universal type
mental purposes and otherwise, but the circuit diagram shown in Fig. 6 may be considered typical of
the principle in general use.
In this case we find that the condenser is in reality two condensers, a running condenser and a starting condenser, both of which are incorporated
in a
metal container outside of the motor.
The starting
condenser as the name implies, is brought into use
while the motor is starting, and is connected on one
side to the line, and on the other to the starting winding. A centrifugal on the rotor disconnects
the starting condenser as soon as the proper speed is
Capacitor motors cause no interference
with radio reception.
eoretical ~~grem of cne form of caFig. 6.
paci~r motor
The synchronous
motor has a
use in certain industrial fields where constant speed
is of prime importance,
but it finds no place in doAside from the
mestic or ordinary
iarge industrial
centers few service men will ever be
called upon to repair motors of this type.
Polyphase motors comprise the second group of alternating-eurrent
motors. Two and three-phase
induetion motors have their windings so*connected and
plae~ aa to make use of polyphase electrical energy.
are placed in the stator, while the
rotor, wnich in reality is the “field” of the machine,
is not connected to any source of electrical energy.
The rotor is excited by the induction set up by the
stator windings.
Polyphase motors of the induction
type have their greatest torque at t~he instant power
is applied, .and before the rotor starts to run. Therefore, and unlike the single-phase
the polyphase
motors are entirely
~a~aPie circuits of two-phase motors
st,arting without the aid of auxiliary
windings or
other devices.
3lost two-phase motors can be recognized b:; observing the number of iine terminals, which will be
~OUFin number.
These are often called two-phase, 4
wire motors, a fact which denotes that the windings
are not interconnected.
A few interconnected
twophase motors, known as two-phase, 3 wire machines,
are in use and have three line terminals the same as
three-phase motors. The diagram at Figure 7 shows
the circuit~s of both types.
Three-phase motors have their phase windings arranged in a great rariety of circuits depending on
the manner of interconnectiug
the phases, number oi
poles, number of paths and other considerations.
otors of this type have their windings classified
mto two groups according to the method of interconnecting the phase windings, as Star connected, or
Delta connected.
Figure S gives a theoretical
diagram of each of these types.
From the diagram it wi:I readily be seen that in the
star form of winding the ends of each phase winding
are connected together at a central point, more often
called the “start point.” The other, or leading ends.8
of each phase are connected to the line terminais.
elta connected winding we see that each
end of a ~~~s~windi~~
is connected to the end of
another phase winding, so that the three phase windings form the shape of a triangle.
Fig. 8.
Three-phase motor circuit types
Other terms used in connection with the windings
of three-phase
motors might be of interest to those
not well posted on the subject.
When a three-phase
motor is designated as “2 pole”, “4 pole”, “6 pole”,
etc.. it does not refer to the total number of poles in
the motor, but only to the number of poles comprisThus a three-phase,
ing one of the phase windings.
2 pole motor winding will have 6 poles, two for each
of the three phases.
In the same way a three-phase,
3 pole winding will have a total of 24 poles for the
three nhase groups.
The term “1 path”, “2 path”, “4 path”, etc., refers
to the number of current paths through each of the
phase windings.
This will perhaps be better understood by consulting
Figure 9. It should be noted
that these schematic drawings show only the electrical circuits and connections
of the motor windings, and not the relative positions of the coil groups
in the statoF
In practice a coil belonging to one
phase group is followed by a coil of the second phase
group, and that in turn by a coil of the third phase
group, and this order is repeated around the stator.
A diagram of the actual arrangement
of the phase
groups’for a three-phase, 6 pole, 3 path, star winding
is shown in Figure 10.
single path and a four path delta winding
Fig. 10. Circuit diagram of a 3-phase, 6 pole, 3
path, star winding
HE several types of split-loop windings have
over the regular
loop winding discussed in the previous article.
Some of t.he advantages of t,he split-loop winding are
that it aids in giving better space distribution
the ends of.t.he winding, and that it gives a more even
mechanical and electrical balance.
The latter is especially true in the case of the parallel wound type
of split-loop winding.
Here we find that the coils are wound in pairs,
parallel to each other and one on each side of the
each pair of coils that are parallel to each other are of the same length, and hence
will be of the same weight and electrical resistance.
In the plain loop winding each one of the coils will be
slightly different in these respects while in the splitparallel-loop
winding the number of unlike coils is
reduced by one half, Another advantage of this type
of winding is that it can be wound with more than
one wire in hand if required.
The only valid objections to this type of winding can be summed up by
saying that it is slightly harder to connect up, that
it is easier to make mistakes than in the piain loop
winding, and that the wires must be cut at the completion of each coil.
The different types of windings discussed here are
all chorded. By “chorded” is meant that the coils are
wound less than full pit~ch. If an armature has, for
instance, 14 slots, the full pitch for a two pole machine would be in slots 1 and 8, those diametrically
opposite each other.
When the windings are placed
less than full pitch, as in slots 1 and 6, or 1 and 7,
the winding spans less than the full distance
between pole centers and is called a chorded winding.
Figure 2 shows the method of starting and finishing a parallel split-loop winding. Arbitrarily,
an armature having 14 slots has been chosen for purposes
of explanation,
but”any armature with an even num,,.,~~ 70
her of slots can be wound in the same general manner. The first coil is st.arted in the slot selected as
number 1 and comes back in slot 7, then back
through slot 1 and so on around until the correct
number of turns have been placed. The wire is now
cut at the commutator end, leaving ample length to
reach the proper commutator
bar with an inch or
two left over. A piece of white sleeving should now
be slipped over the starting end of the coil while a
piec,e, of red sleeving is nlaced arotind the finishing
end. ” This method of marking is followed on each
coil as it is completed so that all starting ends and
all finishing ends will be coior coded the same.
When the first coil is completed the armature is
turned one half way around so as to be in position
to receive the second coil. An inspection of the diagram will show that the second coil goes into slot 8
and 14. A white and a red sleeve are slipped over
the starting and the finishing ends of the second coil.
The armature is now again turned until slot 3 is in
the top position. The third coil is found in slots 3 and
9, and the parallel coil in slots 10 and 2, starting in
slot 10 and finishing in slot 2. The fifth coil is started in slot 5 and finishes in siot 11, while its companion coil, No. 6- starts in slot 12 and ends in slot 4.
We have now arrived at a point where all the slots
hold one coil side except slots 6 and 13 which are stil!
vacant. These slots are opposite each other and can
not hold sides of the same coil, hence it is at this
point where we must start to overlap and start the
second layer.
Coil 7 starts in slot 7 on top of the
first coil laid (No. 1) and ends in the otherwise
vacant slot No. 13. Moving over to slot 14 we start the
8th coil in top of coil No. 2 and finish it in slot 6
which was heretofore
The rest of the coils
forming the top layer are now wound in the following
Coil 9 starts in plot 9 and finishes in slot 1,
coil 10 starts in slot 2 and finishes in slot 8, coil 11
starts in slot 11 and finishes in siot 3, coil 12 starts
in slot 4 and finishes in slot 10, coil 13 starts in slot
13 and finishes in slot 5, coil 14 starts in slot 6 and
ends in slot 12.
In the type of winding under consideration
at this
Fig. 1. End view of a parallel-split
loop winding
point there is a slight difference
in the arrangement
of the coils depending upon the fact of whether or
not the number of armature s!ots is divisible by 2 or
4. Rather than take up time and space by going into
details of the two variations it has been thought better to condense such information
into a table giving
the winding data for armatures
having from 10 to
24 slots.
This winding chart is shown as Figure 3.
Another form of the chorded split-loop winding,
employed mainly on small two pole motor armatures,
is what might be called a divided split-pitch
This form of winding differs from the one
~ just cqnsidered in that two full coils are wound in
but three slots.
As will be seen in the typical example of this type of winding shown in Figure 4, two
coil sides are wound in slot No. 1 with the remaining
sides of each coil going to adjacent slots on the same
side of the shaft.
In this case we have an armature
with 24 slots. The full pitch for this armature would
be 12 slots or 1 and 13, a winding which would tend
Fig. 2A.
Starting a parallel-split loop winding
to “pile up” at the ends because each coil would have
to cross the largest number of other coils besides
bending around the shaft.
By making the winding short pitch, or chorded, we
eliminate a great part of this trouble. If we make the
pitch I and 11 instead of 1 and 13 we are covering
two slots less than full pitch, which helps some but
may not solve ali of the difficulty
of getting the
windings in the space allowed. As a further aid to
securing a better distribution
of the coil ends the
divided, or split-pitch
winding is often, used. This
winding is wound with one wire in hand, and can be
used on armatures having two or four times as many
commutator bars as slots. It can be loop wound with
Complete diagram of a parallel-split loop
a continuous wire, in which case the loops must he
color coded alternately.
In winding the armature shown in Fig. 4 the first
coil is started in slot 1, carried through slot 11, and
back through slot 1 until the full number of turns
The finish of the first coil is in
have been wound.
the same position as the beginning-at
the commutator end of slot l-and
a loop long enough to reach
the proper commutator
bar is made before starting
the second coil. Coil two is also started (from the
loop) in slot 1, but instead of also goin,g through slot
11 it is wound into slot 10. Thus the pitch of the
coils is split between 1 and 10 and 1 and 9. Half of
the coils will have a pitch of 10 slots, half will have
a pitch of 9 slots, the average for the whole winding
will be 9% slots, or a pitch of 9.5. Coil three starts
in slot 2, carries through slot 12 and finishes with a
loop in slot 2. Coil four starts in slot 2, winds in
slot 11 and finishes with a loop in slot 2 ready to
commence coil five in slot 3. This method is carried
on around the armature until each slot contains four
coil sides.
Still another type of loop winding is known as the
split V laop. The chief advanta,ge of this form of
winding will be found where there is little space ben the bdtoma of the slots and the shaft. Because
coils are split, one coil end from each V shaped
goes on each side of the shaft as seen in the ilation
in Figure 5. While this winding is wound
oops between coils it can not be connected like
lar loop winding. In this case the loops must
efore connecting to the commutator and it is
nt that the colored sleeving be around each
starting and finishing lead and not mercIy slipped over the loop. Then when the loops are
cut the proper designation
can still be told. To accomplish this a dozen or more pieces off sleeving,
red and white, are slipped over the wire
before starting the winding.
A white sleeve can be left on each starting lead
and a red one on the finishing
end. A loop is then
made in the wire, then another white sleeve is put in
place, and another coil is wound. Whenever the supply of sleeves on the wire runs out the wire must be
cut and a new supply slipped over the wire as in the
With this kind of winding a slot will be
completed as soon as the two coils are wound. and it
can be wedged at once if desired.
This winding can
only be used on an even number of slots.
Another form of winding which is adaptable particularly for low voltage armatures where the gauge
of the wire is large and the turns few, is what is
As a windknown as a diametrically
split winding.
ing of this kind must be full pitch to be symmetrical,
it can only be used where the slots count up to an
even number.
In the diametrically
split winding each coil is di15
: 1:
e I
,” :
: :
8 s
I 0
I :
1; G
1: ‘:
1: :
D 1.7
la a
u ~1
6 1.
3,”3d :,““j
1 ..
1 L. --gqj;
,” b.
,: &=
3 :
1s I
1: lE
7 li
D d
2s LO
Is aa
Bd u
* 2
1* s
6 u
18 8
6 1’
m ?
B re
To G
Fig. 3. Winding chart for split loop armatures having
from 10 to 24 slots. Compiled from tables in Rewinding Small Motors, by Braymer and Roe
vided in half as it is wound, the two halves going on
opposite sides of the shaft.
When the winding is
started several turns are passed to the right or left
of the shaft, then a like number are wound on the
other side of the shaft, and so on back and forth until
the full number of turns have been made. Figure 6
till give a clear idea of the method of placing a
winding of this type.
In the foregoing
has been
made to give a general idea of the various types
of windings
that are often used in small motors
and geners.tors
on direct current.
detailed treatment
would take up an undue amount
of space. It is seldom t,hat a stripped
comes to the rewinding
shop, but. when it does a
general knowledge
of the different
be of value during the process of “engineering”
winding to replace the original.
Usually, and also fortunately
for the rewinder, the
is usually delivered for repairs with the
old winding more or less intact, and the necessary
Fig. 4.
ivided split-pitch loop winding
data for winding can be secured before stripping. If
it is known or can be ascertained that the now defective winding has given long and satisfactory
the rewinder can hardly do better than to copy the
old winding in such details as pitch, size of wire,
kind of insulation, number of turns, etc. Naturally
many rewinders
will have pet methods that have
proved their worth, new and better materials may be
on the market, and it is quite all right to make legitimate substitutions
that are known to be good.
When an armature winding is an unknown quantity it should be hand stripped down to a point where
the winder will be absolutely sure that he is famiilar
with the commutator connections and all other information.
In such a case, or where this information
already on file from previous jobs of the same kind,
the balance of the stripping job can be done in the
quickest and best manner.
One method of stripping small armatures that has
found favor in many a shop is to cut off all the coil
ends at one end of the core. This can be done with a
hacksaw or on a lathe.
The armature is then placed
over a low burning gas fire or in a hot oven and allowed to “bake”.
The commutator
can be removed
or not, depending on the proximity to the windings,
its construction
and the type of heat used to bake the
old winding.
should never be placed
over a flame.
Fig. 5. End view of a split-pit&
loop winding
After the winding has been thoroughly
baked the
shaft can be bumped sharply when in a vertical position and the winding will slip out of the core. If
the baking has been thorough then slot insulation will
usually come out with the coils, but if not it can
easily he cleaned out with an old hacksaw blade.
Usually armatures are wound with the coil ends at
This allows
the drive end closely hugging the shaft.
more room for distributing
the coil ends and shortens
the distance the wires must travel betwes+n slots.
Some armatures,
however, are wound with iy hollow
space between the shaft and the windings.
The reason for this is either because there is a projection of
the bearing boss of the end bell, or else to improve
of the winding.
To form a hollow end in the winding a wooden
spool is first slipped over the shaft. and the windings
are then~ wound tight around the spool. Every shop
should have a set of these spools available in sixes to
Fig. 6. A diametrically split winding.
This is
wound full pitch or “on the half”
fit shafts from 1/2 inch up to at least 1% inches diameter. An assortme’nt of outside diameters will also
be necessary in as much as the spool must be smaller
than the radius of the bottom of the armature slots.
Usually the spool will be at least a $i inch below the
bottom of the slots. After the winding is completed
the spool can easily be slipped off of the shaft by
giving a quarter turn.
Some form of counting device is a very handy piece
of equipment for the rewinding bench.
and stators used on the higher voltages often have
a considerable number of turns per coil and an exact
count of the turns wound is very desirable.
In the
large shops and in the factories the winder will be
given a job and allowed to stay with it until through.
In the small shop, however, different conditions prevail. The rewinder may have a dozen other duties,
such as answering the phone, waiting on customers,
doing minor rush repairs, etc., all of which distract
attention from the winding job. A turn counter can
be rigged up for use when laying hand windings that
will allow the winder to stop at any time and yet
come back to the job an hour, or a day, or a week
later and know exactly where be left off. The counter
can be operated by the hand or foot in some ingenious manner.
The writer uses one made from the
trip mileage assembly from an old speedometer which
is very satisfactory.
Counters for all kinds of industrial jobs can be purchased at moderate prices, but
if one is purchased get one that can bc reset to zero
TEE course of a year many types of armatures
will come the way of the rewinding shop and it
is neceesary for the winder to have a comprehensive knowledge of the various forms of windings.
One of tbe most common types is known as the loop
On a loop wound armature one complete
coil end, or loop, can be seen on the driving end. This
is, of course. the last coil wound and is the only one
not partially covered by adjacent coil ends. See Fig. 1.
Because consecutive coils finish and start in slots
next to each other, and because bcth of these leadethe finish of one coil and the start of the next-go
to the same bar on the commutator,
it is not only
possible but often practicable
to wind the armature
with a continuous wire. When this is done a loop is
made long enough to reach the proper commutator
bar at the finish of one coil, and the wire is doubled
back to start the next coil. A study of Figure 2 will
show the manner in which this is accomplished.
Loop windings are quite popular on small armatures, such as are used in vacuum cleaner, fan and
most universal type fractional
One of the reasons for this is that such armatures are
most often wound on armature
winding machines,
and the loop winding is most adaptable to this form
of production. Most rewinders find it not only tedious
but unsatisfactory
to attempt to rewind very small
without the aid of a winding machine.
oat of these armatures are wound with plain enameled wire of small diameter and require an even
tension to prevent breaking of the insulating
resulting in shorts.
Few rewinding shops depending on local trade will
find it worthwhile to install an armature winding machine for the comparatively
few armatures
that can
not readily be hand wound. There are many concerns
making a specialty of machine winding small armatures and usually an exchange plan is offered giving
raneeof the end of a loop winding.
quick service and low cost. In general, hand winding
will be found satisfactory
on armatures
cotton covered wire if the price received for the finished job is in proportion
to the labor involved.
la brief, the advantagea
of the loop winding are
that such a winding is quickly wound, and the connections to the commutator are easily made with the
amallest chance of error. The chief disadvantages
this form of winding lies in the unequal amount of
copper in the various coils, and in unequal mechanical
balance. Because the coil ends must be built up, one
upon the other, it will be seen that the last coils laid
contain a greater length of wire than will the
first coils placed in the slots.
Thus there will be a
vatiation of the electrical resistance
of the different
as well as a difference
in weight.
ny beginning rewinders experience great diffilty in securing a symmetrical
winding because of
e tendency of the coil ends to “pile up,” with the
nding would appear if wound
beginning end of wire.
een edik so as tu have continu
C, wire to reel used in winding.
result that tbe finished winding occupies too much
space, and may even result in preventing
its assembly into the machine.
There are three tricks well
known to experienced rewinders which will overcome
this tendency.
Tbe first and mobably most important rule to remember is that the first three coils laid determine
tbe shape of the finished job, for it is over this position that the last coils overlap. Therefore, particular
attention must be given to the first few coils in the
way of pressing them neatly and closely against the
core and close to the shaft.
in this connection
it might be well to state that
fibre end laminations
should be used whenever possible. These fibre washers can be purchased in sizes
and shapes to fit all standard type cores, and a reaaonable stock of them should be maintained. Their use
one of the greatest troubles that bothers
the winder, that of grounds at the corners where the
wires leave the slots. When no factory cut end wash83
Fig. 3. Showing proper use of fibre end laminations pressed on shaft.
era are immediately
available, some rewinders take
the time to hand cut a set from sheet fibre. When no
other pattern is at hand one of the iron laminations
can be pried from the core and used as a pattern, after which it can be replaced. Figure 3 shows the use
of these fibre laminations,
while Fig. 4 shows the
method of laying coil ends when regular core insulators are not available.
The writer knew of one fairly large rewinding
shop which discontinued
the use of these insulators
some years ago wit.h apparent
most of their work was in the field of low voltage
automotive armatures,
and they used an unusually
heavy type of slot paper with generous margins. Fibre end laminations
must be used if the utmost in
long life and dependability
are expected.
The method of placing a loop winding is as follows :
Start the wire in slot No. 1, leaving sufficient length
to more than reach the commutator
bar to which it
will later be connected, and bring around through
slot No. 7 as shown in Figure 5. (In this case we
are arbitrarily
taking an armature
having 14 slots
with a pitch of 1 and 7, or one slot less than half way).
The wire is then taken back through slot No. 1, around
to slot No. 7, then back through No. 1 and so forth
until the required number of turns have been made.
The wire is then carried out past the commutator,
twisted into a loop. and is brought back into slot
No. 2. The coil occupying slots No. 2 and No. 8 is now
ow to insulate armature c
tions are used. A, wedge.
, round fibre washer. E, shaft insu1atioR. F, air space.
wound, leaving another loop at its completion.
coil in slots 3 and 9 is now placed. followed by the
other eleven coils. At the conclusion of the winding
operation there will be 13 looped ends plus the single
and finishing
ends. These two single ends
can be twisted together, after which the loops can be
placed in the proper commutator
bars in order of
As this particular
armature is one wire in
hand there will be 14 bars, or one bar per loop.
Another rule that then experienced winder follow8
tomavoid bulkiness in the winding is to “fan out” the
coil ends. This means that instead of laying the wires
in a more or less round bundle as they are in a slot,
the winder spreads the wires out fanwise at the ends
where they must pass across other coils. This procedure utilizes the space to the best advantage and
tends to keep the layers thin and closer to the core.
See the diagram in Figure 6.
Still another method of keeping the coil ends closely packed and symmetrical
is to make frequent use of
a hammer or small mallet. The blows should not be
applied directly to the coil ends but through the med85
ium of a small block of soft wood, one with rounder
corners. The blows .should not be heavy, as considerable caution must be used to avoid cutting through
A little practice will soon show where
the insulation.
and how much pressure can be applied for the best
Eo far we have considered oniy the loop winding as
wound with a single wire.
They can, however, be
wound with two or three wires in hand, or else the
operator if he wishes can wind two, three or more
coils in the same slot with a single wire. In this latter case-using
but a single wire-the
first coil is
wound in the slots, then a loop is formed the same
as for the single coil winding, another coil is wound
in the same slots and on top of the first one, another
loop is formed, and additional coils are wound in the
same manner.
In a winding of this kind the number of coils per
slot is determined by the relation of commutator bars
to slots. Thus if there are I4 slots and 42 bars it will
l-0 MAKE
Fig. 6.
Spreading out coil ends prevents bulkiness.
be a case of 42 divided by 14, or 3 coils per slot. With
the one wire in hand method of forming more than
one coil per slot, each loop will be the start of one
coil and the finish of another. However, there is dan-r
ger of getting the loops from t,he different
mixed when assembling
to the commutator
and for
this reason winders use several ways of marking the
loops of the first, second, third, etc., coils. Either
coIored woven sleeving can be slipped over the different loops-such
as red for the first, black for the
second, blue for the third, or else the winder can
leave a short loop on the end of the first coil, a longer
one on the second, a still longer one on the third, etc.
Fig. 7. When a ground occurs in winding, the test
lamp lights at once.
When winding an armature
with more than one
wire in hand the wires are usually cut at the completion of each set of coils and it becomes necessary to
brand the ends. This is most often done with colored
sleeving but only two colors are needed as all finishing ends can be one color and all starting ends of
a different color. As an example plain white sleeving
can be used for starting ends, with blue for the finishing leads. This sleeving is not wasted as it can be
left on the wires to form an extra layer of insuiation
going to the commutator where the wires are bunched.
One advantage
of the continuous
wire system in
winding loop wound armatures
lies in the fact that
grounds can be instantly detected if the beginning of
the winding is connected to one side of a test lamp
or buzzer, and the shaft is connected to the other side.
As soon as a ground appears the lamp will glow, or
the buzzer indicate the trouble, and the win;er can
remedy the fault at once before covering the place
with more turns.
See Fig. 7 for diagram.
While the armature coils of the higher voltage machines, with certain exceptions,
usually contain a
!arge number of turns of relatively
small wire, this
fact is not true with machines operating on 32 volts
and less. Here we most often find very few turns per
coil, in the neighborhood
of 6 to 10 or so, and the
wire possibly between number 12 to 18 gauge.
individual coil on an average armature of thia type
will be found to contain anywhere from 6 to possibly
16 feet of wire. Hence many rewinders resort to a
scheme of winding that eliminates
all bother of
counting turns.
The simple method by which this is done is to measure the wire from one of the original coils, and then
to cut a bundle of new wires about six inches longer
than the sample. This extra length, of course, ie to
compensate for inequalities
in winding and to allow
plenty of length for the commutator leads. The winder
en draws wires from the bundle and winds turns
into the slot until all of the length has been placed.
As mentioned before in connection with this type of
winding, the last few coils will need slightly more
wire than will the first coils, due to the greater distance t,be last coils have te travel over those beneath.
This method of winding will be found very handy
for the man who is constantly
called away from the
winding bench to answer telephone calls, or to do
other work. The freedom from having to count or to
remember the number of turns made will allow the
winder to get back on the job with the least loss of
time and the fewest errors.
When connecting any type of winding to the commutator it is found to be very handy if all of the finishing ends of the coils can be made to come out on
the top layer, just under the wedge.
This gives a
pleasing contour to the finished job and is the way
most armatures are wound.
Taking a 14 slot armature as an example, with a
pitch of 1 and 7, we find that the first 6 coils wound
lie wholly in the bottom of their respective slots. At
this point we have six coils with 12 coil sides occupying 12 slots, with two slots still vacant. Our next coil
to be wound will start in slot 7 which already holds
the finishing
side of the first coil wound, and we
have to do something about it if we do not wish to
cover up the finishing
end of the coil starting
slot 1.
What is done is to lift out the finishing
end (or
ends if more than one in hand) and bend it back
away from the rear of the armature.
We now wind
in the coil that takes position in slots 7 and 13. After
ail is in place we bring back the finishing
e first coil that was in slot 7, and which was
rarily removed, and replace it in the top of slot
1 okowe the iast wound coil. Thus we have the finisklead from the lower coil coming out on top of the
In the armature
we are considering
ust be done in each slot from No. 7 to No. 14, Slots
o. 1 to No. 6 will have the finishing
leads coming
out on top a8 a matter of course.
Loop windings can be wound either right or left
without affecting armature rotation or polarity.
ght or left hand is meant the direction in which
the coils are placed one upon the other. The winder
can wind either way from him or toward him, and
the coils can be placed on either side of the armature
shaft in making the circuit from slot to slot.
The winding pitch of an armature
is found by
equating the number of slots spanned by one complete coil, including the slots in which the coil rests.
In the fourteen slot arma.ture we have been considering the pitch is 1 and 7, meaning that one side of
the eoii is in slot No. 1 wkile the other side is in slot
No. 7. For a 2 pole machine of this type the full
pitch would be 1 and 8, or in slots exactly opposite
each other. As the pitch in this case is one slot less
than full pitch it is commonly known by the winding
term “chorded.”
In a machine of four or more poles
the “full pitch” would be the number of slots necesr-y to span the space between exact centers of adjacent poles.
ANY are the electrical
that are
brought to the average electric shop for repair. A very fair proportion of such appliances needing service will be fans of one kind or another, and other small single phase motors used in
the home, shop or office.
The profit from this kind of work depends almost
upon the judgment
and experience of the
serviee man. Judgment must be used to decide whether it will be best to take the job in for repairs, or
wketker the customer should be sold on the purchase
of a new and better fan, vacuum cleaner or just extractor. Each case must be considered on its merits,
but as a general rule it is poor policy to accept a repair job if the estimated
cost of reconditioning
small appliance exceeds 60% of the price of a new
Unless, of course, the customer insists that
the work be done regardless.
Suck a policy leads to
more sales, better profits, and in the long run to more
of that red blooded business commodity known as
good will.
A certain portion of the market has been flooded
with cheap 10~ store merchandise:
49c toasters, WC
electric stoves and fans for $1.19. Obviously it is impractical to repair and impossible to make any profit
from this kind of business, and the sooner suck items
land in the junk box the better for all concerned. Experience will teach a service man that many an expensive appliance should be treated with a hands off
policy when it comes to the shop for repairs.
may be because parts are hard or even impossible to
obtain, because the amount of labor involved would
be out of proportion to the value of the unit, or kecause new inventions
or improvements
have made
the outfit obsolete.
any electrical repairmen, while familiar with the
oper~tio5 of small single phase motors above the l/8
horsepower size, keeitate to dig too deeply into the
miniature single phase motors because they are not
familiar with the various starting and speed control
circuits used on so many fans and other appliances.
Some of these circuits seem quite complicated when
seen ip the final assembly, and are often very hard to
trace out if no diagram is at hand. As most repair
men know, it often takes ten times as long to locate
the trouble as it does to fix it when once found.
The purpose of this article is to explain, and show
by simple diagrams, the circuits commonly used in
fan motors, especially
in the older
models. Because of space limitations
the exact circuits for all makes and models cannot be given, but
it is believed enough are described here to give a
working knowledge of the principles involved.
The earliest type of alternating
current fan motor
was copied from the direct-current
fans in use at
that time. It was discovered that a series type motor
would run on a-c as well as d-c. with the exception
that the use of a-c current caused excessive sparking
at the brushes. This complaint was diminished somewhat by making slight changes in the winding of the
armature and field windings.
There remained, however, the matter of speed control. On the earlier motors this was accomplished
by shifting the brushes
from the neutral position, as indicated in Figure 1.
In later types, many of which are in use today, the
speed of the fan is controlled by inserting a resistance in series with the motor circuit, thus lowering
the voltage applied to the motor windings. This, of
course, reduced the speed of the armature in proportion to the value of the resistance. Many of these fans
have a single resistance,
giving a high and a low
speed; others use a tapped resistance giving three or
four speeds.
A diagram of the circuits of a simple
three speed fan of the commutator-series
type is
shown in Figure 2.
The next step in the advancement
of fan motor
design was the use of an induction motor of the
simplest type. These motors made to operate on 60
cycle current empioy four poles to obtain the most
speed for the most common type of fan
the .neighborhood
of 1600 r.p.m. Many of
Fig. 1. Old style fan motor of the serias
PY with speed regulation obtained by shifting brushes .
the cheaper fans used a cast field ring, but because
of the heavy losses common to this type of construction most of the better fanp used a laminated field
Since induction
motors are not inherently
some means of causing a displacement
the pole flux had to be provided to cause the rotor to
start revolving. One means of accomplishing
this was
by shading the trailing edge of the poles, thus retarding the flow of magnetic flux in that section of the
pole surrounded by the copper band, while in the rest
of the pole the flux is in phase with the field current.
Shaded coil construction
costs and will be found in many of the cheaper induction motors in this type of service.
Induction type fan motors use a squirrel-cage
somewhat similar to the rotors used in larger induction motors.
The copper squirrel-cage
of the typical fan rotor, however, has a higher resistance than that of those used in motors for power
This higher resistance
of the squirrel-cage
rotor is necessary where the field strength is to be
Fig. 2. Circuit of a series-commutator fin
motor with speed control by a tapped
reduced in the controlling of fan speed. As the voltage applied to the stator winding is reduced it decreases the density of the magnetic flux and allows
greater slippage of the rotor.
The speed of shaded coil motors is usually controlled with the aid of a choke coil or resistance
placed in series with tbe main field. A diagram of
a typical single-phase
fan motor of the shaded pole
type, one employing a resistance
unit for speed
changes, is shown in Figure 3.
A common type of ceiling fan is similar in principle to the ty e just described.
Some ceiling fans
make use of copper band shading on the individual
poles while others use a continuous shading coil that
is wound through the slots on top and isolated from
the main winding.
The terminals of this shading coil
are soldered together
to make a complete circuit
Fig. 3. Single-phase motor of the shaded coil
type. A tapped resistance controls speed
having no connection with line voltage at any point.
The continuous wire wound shading coil balances the
flux in all poles alike, and makes for a
smoother and more quiet running motor.
Because of the lower speed at which they operate,
all ceiling fan motors have a larger number of poles
than does the conventional
desk type of fan. When
ceiling fans become noisy in operation the trouble
ean usually be traced to lack of lubrication
or wear
in the rotor bearing.
If excessive the latter condition may allow the rotor to scrape against the poles.
Figure 4 shows the circuits of a continuous coil shaded ceiling fan motor, the speeds of which are regulated by a four pole snap switch and a center tapped
choke coil.
Split-phase is used in starting fan motors just as
it has been used in the larger size of power motors.
Fig. 4.
Circuits of a ceiling fan motor using
a wire wound shaded starting coil with choke
coil for speed control
of phase splitting
have been
brought into use on different
makes of fans, and a
few of the common circuits will be briefly considered.
Figure 5 shows the simple circuit details of a splitphase fan motor having a main and a starting winding. It will be noted that the starting winding is in
the circuit at all times. This simplifies the operation
of the fan, as a centrifugal
or cutout switch is eliminated from the starting circuit, but means that the
starting winding, by being in the circuit at all times,
must have a very high resistance.
As a fan motor is
not required to start under any load other than bearing friction,
the starting
winding can be of much
Fig. 5. Spiit-phase fan motor with high resistance starting winding, which is permanently
connected in the circuit
higher resistance than would be possible in a motor
having to start under full load. Motors of this type
are not economical in current consumption
as the
starting winding continues to draw current as long
as the fan is in operation. Speed control in this type
of fan is usually by a resistance
coil having one or
two taps.
In Figure 6 we have a split-phase
fan motor circuit
very similar to the one in Figure 5 except that a centrifugal
switch has been placed in series with the
winding. Here the starting winding would
be heavier wound as !t is in use only during the starting period.
Having less resistance
it will aid the
rotor to attain running speed in a shorter period of
time and, while it will consume more current, this
can be disregarded
due to the short space of time the
winding is brought into use. A choke coil
in the fan base controls the voltage impressed on the
winnings and gives a number of speeds correspond.,,
to the number of taps provided.
A very efficient type of desk fan that has been produced in large numbers is shown in Figure 7. This
type of fan circuit is familiar to most service men as
it is one of the types having a three conductor cable
connecting the motor with the base. The motor winding circuit is like that of Figure 6 with the exception
that the centrifugal
cutout switch is not used, one end
of the starting winding being directly connected to
one end of the main or running winding.
The features of this design are a high starting torque, better
than average efficiency at running speeds, and good
speed control.
A transformer
is to be found in the base of a motor
of this type. The transformer
primary is tapped at
several points and is placed in series with one lead of
The transformer
secthe main, or running winding.
ondary is connected to the motor side of the primary
at one end, and to the free end of the starting winding on the other side. When a circuit of this type is
thrown on the line the current for the main winding
has to pass through the transformer
primary, and
the voltage induced in the secondary winding of the
is fed to the starting
winding circuit.
The voltage lag in the secondary of the transformer
plus the normal lag in the high resistance starting
winding gives a phase-angle
almost equal to a twophase motor.
This accounts for the high starting
torque in this type of fan, and has a lot to do with
quiet operation at all speeds.
Anot~her type of fan motor circuit using a three
conductor cable between the base and motor eliminates the use of a starting winding by dividing the
main winding into three parts, and placed in relationship to each other so that the flux of the field
has a rotating
closely associated
that of a three phase motor. One end of each of the
three sections of winding are connected together inside the motor.
Line current is fed directly to the
ig. 6.
Circuits of a split-phase fan motor
ut switch in series with the rtari-
free end of one winding, and after passing through
it, is distributed
into the two remaining
From the second section of the winding the current
must pass through a resistance
to reach the other
side of the line, and A-Y...
--&ion must pass
11.u +WA
“1 .&.a “I
through a tapped reactance
or choke coil. In this
way the current in one section of the winding is
made to lead that of the next section (because the
and choke coils are of different
and the rotor is caused to revolve in the field.
Speed control in a motor of this type is obtained by
adding more or less turns to the working part of the
circuit that includes the resistance and choke coil.
When tbe switch is moved to the medium or low positions more turns are added to the choke coil and to the
resistance, with the result that the voltage applied to
Fig. 7.
Split-phase fan motor using a transfor speed control. Sk% &at the
inding is connected to the transconda~
the motor windings is reduced, and consequently the
speed of the rotor. Any reduction of voltage in the
two sections of the winding connected to the resistance
and choke coils is automatically reflected in the section
of the winding connected to the line, as this winding
is a common path for the other two sections. A schematic diagram of a fan having a circuit of this type is
given in Figure 8.
In the servicing of electric fans the most common
complaints are worn out bearings, stripped gears on
types, and burned out resistance or choke
coils. As a general rule the motor windings give but
little trouble save where the impressed voltage has
se fae motor with windkn
been too high, where the fan has been connected to
current of the wrong number of cycles, or where the
size or number of the fan blades has been changed. Fan
motors are designed to operate at certain speeds under certain load conditions.
When larger blades, or
more blades of the same size, are attached to the rotor
t, the rotor speed will be reduced on the one hand,
while current draw from the line will be increased on
the other.
The same conditions apply when fan mo101
tora are used for other purposes where the load OP
is changed within wide limite.
ANY requests have come from motor shops
asking for general information
on the winding of low voltage armatures
such as are
used in automobile and marine engine generators and
Because it would be impossible to answer
ali these queries in detail, we are giving here a numher of suggestions and instructions
for rewinding six
and twelve volt armatures.
Before going into the methods used in this branch of
rewinding, let us first consider the possibilities
making profits from this sort of work. In the larger
cities the automotive field is keenly competitive and in
many cases prices have been hammered down to bed
rock. For this reason alone the well established motor
shop will not find this form of. rewinding attractive,
and the best interests of all concerned will probably
be better served if the motor shop sticks strictly to its
own field.
In the larger cities there will usually be found one
or more attractive
shops that are on a quanitity production basis, and who, by the use of cheap, unskilled
labor, are able to turn out the work at extremely low
Not only do they use cheap labor but in most
cases they use undersize wire and many other short
No thought is given to
cuts to beat down the price.
quality or lasting service.
At current prices the most popular types of automobile generator armatures,
such as Ford and Chevrolet, can be bought at wholesale as low as a dollar and
a quarter.
Obviously, at this price, considering even
tbr cheapest labor and materials, there can not be
much profit.
The question is often asked: How do
they do it? A visit to one of these production shops
will supply the answer.
The writer recently inspected such a shop. Eleven
boys and girls and one experienced armature winder
were employed in the work of turning out rewound
One young boy, fresh from the farm, did
~othi5g all day long but strip old cores. After stripping, the cores were p!aced in a gas oven to burn out
the remaining paper and dope. Another boy replaced
defective commutators or cleaned up the old ones for
One girl cu: and in,serted the slot insulation. One girl and two boys wound the coils in the
slots, leaving the free ends extended.
Another boy
placed coil leads in the commutator bar grooves, and
em on to another boy who did the soldering.
her boy turned the commutators on the lathe
busy supervising the work and attending to the few
jobs that needed special knowledge.
In this shop not one employee, except the foreman,
was capable of winding a complete armature.
one had been trained to do but one thing, and hamlled
the same operation day after day. The capacity of this
shop was about 500 armatures per day with a labor
overhead of about $30, and it is easily seen that the
skilled armature
winder can not compete in this
So far, from the standpoint of the skilled workman,
we have painted the picture rather dark. There is,
however, another side of the picture if we move to one
of the smaller towns some distance from a large center.
Here, through automotive
jobbers and auto supply
stores we still have the same competition in the small
car generator armature field, but these stores are not
likely to carry akrmatures to fit old, obsolete or high
priceo cars, and these are the numbers that net the
rewinder real money.
It costs but a few cents more to rewind a $5.00 armature (dealer’s price) than it does to rewind an armature for a Chevrolet six, that wholesales for $1.60. It
is the former jobs, the ones selling for $3.60 up to
gIO.00 and over, that offer encouragement
to the motor rewinder.
The volume of these higher priced types
is not large, but to the already equipped motor shop it
offers a chance to fill in odd hours and make wages or
In many instances automotive rewinding has
proved to be a big help to the shop specializing in the
rewinding of a-c motors.
winding fits in well with
the small town motor shop because the same equipment
and stock of materials can be used for both types of
work. Low voltage armatures are easier to wind,
pecialiy for the beginner,
because there are fewer
turns, fewer coils, and less attention need be given to
The wire sizes used in automotive generator armatures are the easiest for hand winding, as
they are neither too small nor too stiff.
Because of
the large demand, commutators, fibre end laminations,
etc., are quite low in price. A good mica insulated
utator for a Chevrolet armature sells for 26~.
be rewinding of automotive generator armatures
is to be a spare time business for the motor shop, a represe~tative stock of rewound cores must be kept on
and so that. exchanges can be made without delay.
The exchange method allows prompt service to the
buyer (who is invariably
in a hurry) and gives the
shop the opportunity of doing the winding when other
work is not pressing.
It is understood that odd types
and obsolete armatures can not be stocked, but as these
much higher prices the shop can afford to
turn them out as special jobs.
The best way for a shop to build up a stock of automotive armature cores for rewinding is to patronize
a local junk yard.
Cores in good condition, but with
burned out windings, can usually be obtained for
about 25~ each, as the junk man has no other market
In selecting cores, particular
for them
should be given to the condition of the laminations,
trueness, threads, centers and to the bearing surfaces.
It will not pay to rewind cores that are not in good
Just as in the winding of any other type armature,
the first step is to secure the winding data from the
original winding, and to set it down on a form card
which can be filed for read,y reference.
In this manner a more or less complete record of all types of armatures can be built up, after which most of the time
that would otherwise be spent in tracing old windings
cm be saved.
If the shop doea a sufficient
volume of armature
wi~~~~ it will pay to uze a burning oven to aid in
of an accurate diagram of
connections for both a ressive winding are indicated
. .
the stripping and cleaning of old cores. After a brief
period in an oven of this type all organic matter is
completely burned and the wire and insulating material are easily removed.
If the commutator is to be
used again it should be removed before the burning
process. Many of the commutators used in late model
use bakelite insulation
between the bars,
In fact, the great majority of
and this is easily ruined.
bakelite insulated commutators are badly chared when
the armature comes in for rewinding, due to overheating in the generator, and will have to be replaced.
Before removing commutators, the distance they are
set back from the bearing shoulder of the shaft should
be measured, and the new one Dressed on the same
distance. Before installing a new commutator, or an
old one, the fibre end or star washer
shcliild be fitted
on the shaft, and the slots in the commutator bars
should be scoured bright to make soldering easy.
A special grade of slot insulating paper suitable for
almost all automotive armatures can be purchased in
IO pound rolls. This paper is about the right width
for most generator armatures, and needs a minimum
A roll of crepe paper about 1 inch wide
of trimming.
is handy for banding exposed parts of the armature
shaft, and for insulating the armature neck between
winding and commutator
leads. Crepe paper can
easily be formed to fit over irregular and tapered parts
of the winding.
With the exception of the Ford model T generator,
most automotive armatures are wound with two wire8
in hand.
It simplifies matters a great deal and tends
to prevent mistakes if one of the wires carries a tracer.
In making commutator connections the winder can then
place the ends alternately
white and tracer, white and
tracer completely around the commutator.
Number 1’7
S. C. E. is the size most used in automotive work.
m-t 2 a,ymm&rical minding it is b& +o
*.. nrrlar
-.-I* tn
*- aplace all starting leads into the right commutator bars
as tbe coils are wound, leaving the finishing ends free
to come out on top of the finished winding.
Care must
be used to get the right commutator
pitch or the
current will be reversed.
pitch is the number of bars that the winding advances.
A change in pitch of one bar will cause the winding to
be progressive or retrogressive
as the case may be. To
explain this matter more fully we will consider a wave
winding (used in a four pole generator) having 21 slots
and 21 bars.
In Fig. 1 we find the pitch is from bar No. I4 to bar
No. 3 in tracing to the right, which gives us an advance of 10 bars, as we do not count the bar in which
the coil started.
As we wind a second coil, also advancing 10 bars, it brings us around to bar No. 13, which is
just behind No. 14, where we started to wind. Then.
because the winding has dropped back one bar in tracing to the right, we have a retrogressive
If. however. we made OUPconnections to the commutator as indicated by the dotted line, advancing 11 bars
instead of 10 each time, we wou!d diacovar that ins&ad
of coming around to bar No. 13, the winding would
cross over the lead to bar No. 14 and enter bar NO.
16 making a gain of one bar in tracing through the
two coils that make one path around the armature.
Because we have gained one bar we call this a progressive winding.
If an armature is wound progressive when it should
be retrogressive,
or retrogressive
when it should be
progressive, it will motor in the wrong direction when
tested inside the generator, and it will not charge if
The armature can be
iven in the original direction.
made to charge in the original direction of rotation if
the field leads are reversed, but such a change is not
always easily made in an automobile generator.
ost of the modern generators,
being 2 pole machines, are lap wound, and two forms of winding are
in current use, hand wound and form wound. In the
former, also called a “balanced” winding, the coils are
wound on a form and then assembled in the armature
elate. This type of winding has a better mechanical
and electrical balance because all coils have the same
h and weight of copper, and hence, the same rece. Two disadvantages
of this kind of winding,
from the viewpoint of the small winding shop, are that
it is much harder to wind in small quantities, and that
in working the coila into the slots there is always considerable danger of breaking through the insulation.
Since straight hand winding can be substituted satisfactorily for the original form winding, most shops
use the latter method in rewinding cores of this type.
The key to a good hand winding lies in the formation of the first three coils. These first three coils determine the shape of the completed winding as all
subsequent coils wound must pass over them.
first coils wound should be made to hug the curve of
the armature shaft and the core ends. It is necessary
to tamp the wires down into the bottom of the slots
and keep them under reasonable
tension. Coil ends
can be tamped into shape by means of a smooth
wooden block and a light hammer.
In hand winding, the first few coils wound will occupy the b&t~m positinn in the slots on both legs, while
In the
the last few coils will occupy only top positions.
latter case, the finishing ends of the coils will automatically come out on top of the winding, where we
want them, but some special provision must be made
to bring the finishing ends of the lower coils to the
One method of doing this is to remove the last
turn of the finishing ends from the slot before
a top coil is wound over it. Then at the completion
of the top coil. and before the wedge is driven, the
finishing ends of the lower coil can be brought up.
ward and placed on top. Since there will be one
set of finishing ends per slot regardless of the position on the armature, there will be no chance of a mistake with this method.
There are a few armaturfzs in the automotive field
that do not follow conventional
Some of
the older Hudson-Essex
wound with one dead ended coil to mechanically balance the winding.
In other words, when winding the
armature with two wires in hand there would be one
individual coil left over for ,which there were no bars
on the commutator.
The ends of this coil must be cut
off and the coil left open circuited.
Generator armatures on the older Packards use 20 slots and 41 commutator bars. Since they were wound two in hand
tkere was one odd commutator bar left over. To complete the electrical path of the winding it was necessay to cross connect one pair of bars on opposite sides
of the commutator.
This abnd other typical types of
automotive windings are shown in some of the accompanying charts.
A very large number of the cheap replacement automobile generator axmaturer on the market are wound
with wire that is one size smaller than originally specified.
Rewinders sometimes fall for the temptation of
cheaper material and labor costs, but the shop that intends to establish a reputation
for a good product
should avoid this pitfall.
The use of smaller wire gives
a higher internal resistance to the winding and will
cause the generator to heat up more rapidly.
If fewer
than the usual number of turns are used, even of the
proper size wire or larger-the
result will be to lower
the efficiency of the machine, and a higher speed will
be required to obtain a normal charging rate.
‘I’he rewinding shop is occasionally called upon to
rebuild or convert an old generator
to a different
Wind chargers, arc weidere and 110 volt generators for public address systems are some of the
common usea of old automobile generators. The change
from 6 to 12 volts, or from 12 to 6 volts is one that is
often requested.
Some experimenting
must go along
with many of these changes, but there are certain
rules than can be followed.
To double the voltage of a generator the rule is to
use a size of wire that is three numbers larger.
wire will be half the cross sectional area, and twice the
number of turns will be used. Thus, if a field coil was
Qr~gi~a~ly wound with 100 turns of No. 18 wire, it could
be rewound, in approximately
the same space, with
turns of No. 21 wire, and would be suitable for
ion at twice the former voltage.
It is not alssible to double the turns on an armature for
various reasons, but if the original winding is replaced
with one of one or two numbers larger, and all vailable space is filled, the results will usually be satisfactory.
Other operations
on the rewinding of automotive
type armatures, such as soldering, turning, undercutting, dipping and baking follow standard practice
and offer few obstacles.
Many motor shops have taken
up automotive rewinding as a side line, and have reached the point where this class of work carries much of
the overhead through dull seasons.
Since it is a branch
of the business that demands little additional investent, and since there is a fairly constant demand, it
is ~mething to consider.
E single-pha~
motor bexauee of its wide use
in domestic and commercial
lications is, and
principal source
perhaps always will remain,
of revenue of the small motor repair shop. Many winders, v&o have ,mastered the technique of the singlephase motor, hesitate to branch out into the two-andthree-phase field for the simpie reason that so much
of the latter type of work is la,rge and heavy, and also
because it requires additional
equipment, materials.
and specialized knowledge.
These are facts that are
well worth considering, and in the majority of cases
the wisest plan is for the small motor shop to act as a
local agent for some concern making a business of repairing the larger polyphase motors.
Numerous requests have come to us, however, for
some information
the rewinding
of the
smaller two- and three-phase motors.
Most of these
requests have come from shops in the smaller cities
and towns where an additional job or two often spells
the difference
between a good and a bad week, at
least from the financial point of view. In most localities. the percentage of two- or three-phase motors in
the small and fractional
horsepower group is small,
yet a job is a job and may be the means of rounding
out a full we&s time.
Many of the winders who have requested additional
on the winding of polyphase motors have
a good working knowledge of single-phase windings,
but want a few more pointers before venturing
either two- or three-phase work. To these men and
others who may be interested, the following notes are
presented in the hope that they will clear up the major
points in which these windings differ from the usuat
single-phase type.
It may be stated roughly that almost all of the
smaller two- and three-phase
motors use one of the
following types of winding:
1. Basket winding.
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Two layer diamond coils, one coil side per slot.
o layer flat diamond mush coils.
4. Two layer diamond mush pulled coils.
5. The flat strap copper conductor winding.
The met
s of forming or placing each type of winddescribed in the order given above.
ing will
There are two prime essentia!s that go with the
basket type of winding. One is that the total number
of etator slots must be even, and the other is that the
coil span, or number of slots spanned by one coi!, mu&
be an odd number. In the latter case the span must be
1 and 6, 1 and 8, I and 10, etc., for to get an odd span
the last number must be even. For an example, let us
consider a 48 slot stator that is to be wound for 4 poles
and three-phase operation.
We will choose a coil span
of 1 and I2 and check it out on a penciled chart to
make certain it will work out. A simple chart consists of the numbers from 1 upwards written in a line
across a sheet of paper, such as that shown in the accomparing
A study of the chart will show
one slot is skipped in beginning each coil so that
there will be a vacant slot available for the finishing
side of some other coil. Almost all basket windings
have only one coil side per slot. The chart below further proves that the winding will work out correctly in
as much as we find that wherever we have either a top
or a bottom coil side marked above or below a slot
nmber, there is none charted on the opposite side of
the chart number. Thus Slot No. 12 has the top side of
Coil No. 1. Slot No. 13 has the bottom side of Coil No.
7. Slot No. 14 has the top of Coil No. 2, etc.
Now to prove our point, let us see if this stator could
be wound with a pitch of, say, i and 9. (See lower
chart in accompanying
In. looking over
the chart, we see that this pitch is not correct because
slot No. 9 would contain two coil sides, as .would slots
11, 13. 15, etc., while the even numbered slots, 1.0,.12,
14, GZ., would contain no coil sides. Therefore, when
uncertain of the proper coil pitch to use, it is a good
plan to chart it out in advance.
In the basket winding any slot can be. called No. 1
for the start, and the throw, or slot for the other coil
side, can be counted in a clockwise rotation.
In wind113
ig. 1.
A typical wound coil 6x a basket
winding is shown here
ing this 48 slot stator using a 1 and 12 pitch the first
five coils, namely Nos. 1, 3, 6, 7, and 9, must be left
with the top sides left out of their respective slots.
These are called “throw” coils and their loose sides
cannot be placed in the shots until other coil sides have
been placed in Slots 2, 4, 6, 8, and 10. The first coil
that can be inserted at both sides in one operation is
the coil going into slots 11 and 22.
Basket coils are first
wound around
apaced pegs on a board. or on a coil winding machine, and are tied at several points to hold the
wires together.
After the coil sides are placed in
their respective slots, the ends are taped from iron
to iron and they are formed to the proper shape by
means of a fiber drift and a rubber or rawhide’
The slot insulation should extend somewhat
from the core and the taping can be made to cover
the slot insulation and make a sealed joint. A typical
basket coil is shown in Figure 1.
The two-layer winding with only one coil side per.
slot usually requires
coils of the
pulled (mush)
type and differs
from the basket
winding in that as many slots are skipped in laying
the coils as there are coils per group (See Figure 2).
-shaped coil of
layer windings
The upper sketch of Figure 3 shows the. arrange‘me& if there are to be two coils per group.
coils are inserted, then two slots are skipped before
The lower sketch
t&reading in the second pair.
shows the arrangement
for this type winding when
there are three coils per group; insert three coil
sides, then skip three slots.
The slots that are
skipped, of course, will be filled later with the finishing sides of other groups.
The possibility of using any given pitch with this
type of winding can be found by making up a chart
as explained for the basket winding.
Two coil sides
can not occupy a single slot and the total number
of coils will be just one half of the total number of
slota. The slots are preinsulated
and the coils are
taped after installation
just as in the basket winding.
Perhaps the most common type of winding for the
amaller polsphsse motors is the two-layer winding
with flat diamond mush coils. These coils are preformed and partSly
taped before they are inserted.
Figure 4 shows one of these coils ready for insertion
in the stator.
Note that the tape extends in an inch
or 80 on what will be the bottom side of the coil,
while on what is to be the top side the tape lacks
Fig. 3. Method of starting 6
ing with one coil side per riot
an inch or so of reaching the band.
The leads are
brought out and insulated near the diamond nose.
The steps followed in placing this type of windA heavy coming begin with the slot insulation.
position cell is formed to fit the slot, with the top
edges slightly
below the slot opening.
Next a
treated cloth “slider” is inserted in the slot as shown
in Figure 5. The winder now flattens out the center
of the u&aped portion of the bottom side of the coil
with his hands, and slips this flattened section into
one end of the slot.
By careful
pushes the coil across the slot until the far end of
the coil will drop into the slot. The coil side, now
in the slot for its full length. is carefuly centered.
Make certain that the “slider” is also in the proper
Flat diamond mush coils, as shown
only ~rtiaily
taped to facilitate
in slots
The top half of the coil requires a little more
time to place. It must be fed into its slot one wire
at a time, and for this reason the top side is not
tap& right up to the bend and beyond as is the
bottom side. The extra taping to cover the exposed
wires of the coil must be done after the coil is in
place. After this insulation
is in place, a triangle
of treated cloth is slipped between this coil and the
coil below for added protection against shorts.
slot, now containing
two coil sides, is ready for
We can now go back to the bottom side of this coil
and prepare the slot to receive the top side of a
later coil. The cloth “slider“ is pulled up along with
the bottom coi! side until the coil side jams in the
neck of the slot, and is then trimmed off as shown
in Figure 6. The coil is now pressed down into the
bottom of the slot, the sides of the “slider” are ben”l
over and a fibre strip is forced down on top.
Another cloth “slider” is used in the same way for
the coil side that will later go into the upper section
of the slot.
Fig. 5. To install flat diamond mush coils in
slots, the bottom coil side is flattened to enter
slot while the top coil is threaded in one or
two wires at a time
The two-layer diamond mush pulled coils form a
type of winding that is similar to a two layer flat
diamond winding in most respects.
These coils are
wound with
double cotton
a shuttle in the form of a loop, or’ in
a regular coil forming machine.
In the former case
the loops are “pulled” out on a universal type of coil
former or “puller,” so as to arrive at the desired
shape. Since the coils for this particular type of winding are not taped, they must be tied together at the
diamond points to maintain their shape.
uses ;iiltaped coils,
Since this tgpe of wind;ng
extra caution must be used in insulating
coils, and especially so between phase coils.
Triangles of a good grade of suitably treated cloth should
be inserted between all coil ends, and in the case of
the phase coils there should be a double layer. These
cloth triangles should be cut to the general shape of
the coil ends but should be allowed to extend at least
a half an inch on each side and at the diamond point,
as shown in Figure ‘7.
inding trouble can usually be traced
r insulation. The proper method of
slots is shown here . . . . .
Winnings with untaped coils are usually used on
motors with sealed end bells.
Dirt, oil, water, other
liquids, fumes, etc., are enemies of insulation,
where these can get to the windings through openings in the motor frame the taped coils will give the
However, there are many motors of
best service.
the dust proof, water proof and explosion resisting
types where the untaped type of coiis can be expected
to give good service. As a general rule, stators with
untaped coils are given extra attention in varnishing
and baking.
Tbe last type of winding to be considered is one
wound with threaded-in strap-copper coils. Few motors of this kind will find their way to the small
motor shop. Where the slot opening is full width,
these coils can be formed and taped before going
into the stator, but with partially
closed slots the
copper straps must be inserted one at a time. To
do thie, the inner and outer turns must be inserted
through the slot first, and the center turns last.
Figure 8 shows the order in which a five-turn coil
would be fitted into a slot, the opening of which is
juet wide enough to pass one turn at a time. The
numbers above represent the order in which the turns
This sketch shows the use of insulate coils and the
h triaagl~ aeon
of winding with “thr
’ coils . . .
occur in the actual coil, and the lower numbers designate the order in which they pass through the slot
And now for a few last notes on these types of windings. When a Finder experiences any trouble in laying any of these windings, it can usually be traced
directly to inadequate slot insulation or to improperly
formed or “sized” coils. Coils should be accurately
wound from a pattern secured from one of the original coils taken from the motor intact. You can seldom
stretch a coil and get away with it with any degree of
Therefore, it is the practice in many
shops to wind the new set of coils slightly larger than
the originals.
If this is done, it often saves a great
deai of time.
On the other hand, coils that are too
large make a sloppy and unsightly job. The best bet
for the beginner is to make up three or four coils and
then try them in the stator before proceeding
wind the whole group. Experience is the biggest factor in tbis job-and
experience comes only through
Phase insulation,
that is, the insulation between
coils connected to different phases, is a very important point on all polyphase motors.
Many rewinders
chalk the dOtB in which the beginning of each phase
group of coils will start.
This gives an accurate reminder of the places where it is necessary to double
The phase coils form the boundary
the ~su~tio~.
between phases and as such are always subject to
phaae potential.
On the other band, coils of the same
phase have but a low potential between them.
Polyphaae windings must be laid out according to
some diagram.
They will either be regular or uniform, alternate or irregular,
in grouping.
In a uniouping, all groups fill an equal number of slota,
and contain the same number of coils. In the case
of an alternate grouping every other group consi8bta
of an equal number of alots and coils. Irregular grouping is sometimes nrxessary because of special conditions, and in such cases there is no apparent systiem
or uniformity in the number of slots per group. T’ley
will, however, have to balance out nearly equal in coils
over the whole of the winding.
w- P
Taping coil ends after the coils are in the sloti is
an operation that must be done with care. The tape
should be applied very tightly and anchored in place
with quick drying dope. The best practice calls for
allowing the slot insulation to extend beyond the core
as much as possible, the tape then being applied over
this to form a perfect bond. If the taping is not snug
and well anchored it will pull away during the forming, dipping or baking process and leave a spongy
mass, or it will fail to protect the coils where protection is most needed.
After all coils have been placed and wedged, the
winding must be inspected for mechanical faults and
teated for electrical defects. Inspection and meaaorement will reveal if any coil ends are higher than the
stator bore, or if they will rub against the end bells
when the motor is assembled.
The coils should clear
the diameter of the stator bore by at least an eighth
of 811 inch if possible. High 4s
can be tamped down
carefully with a fibre drift and a light hammer.
fibre diifts should have smooth surfaces and rounded
Never hit the coils with iron or steel. The
same method should be used where one or more coil
end extend too far from the core and touch the end
housing which may result in trouble later.
@ROD1 Or
s In
in insert-
BE condenser or capacitor type motor has been
used experimentally
for many years.
Xts recent popularity, however, has resulted from the
rapidly developing field of electric refrigeration
has brought about the commercial development
these motors and made them standard equipment on
many of the small compressing units.
Quantity production made the manufacture
of efficient low-priced
condensers possible and led to the almost universal
adoption of this type of motor in household refrigerunits and in other fractional horsepower driven
uch of the credit for the design and improvement
of the capacitor motor must be given to Professor
Benjamin F. Bailey of the Department of Engineering
Research at the University
of Michigan.
Experiments with motors of this type between the years
on single
one phase
Fig. 2.
a condenser motor.
o-phase diagram in F
1999 aud 1929 were financed by the Detroit Edison
Company in the interest of the entire electrical industry.
There are several reascns why the capacitor motor
replaced the types nf motors formerly used. First,
the condenser xnotor $2::. IShigher efficiency than other
single-phase motoa 2 1:3c~~nd, it has a higher power
factor; third, it ?.z excellent starting
tics; fourth, it is ezzple iu construction;
and last, it is
quieter in operation.
Every one of these features is
valuable in any application, but especially so in the
modern domestic type of refrigerating
In d?&ign the single-phase capacitor motor is very
much like the two-phase induction motor except for
the fact that the two windings need not be similar.
A two-phase motor can be operated from a sing!ephase circuit if a condenser of proper capacity is inserted in one of the phases.
See Figure 1. Some
form of automatic switch is incorporated in almost all
single-phase condenser motors to reduce the effect of
the condenser when the rotor attains full speed. If
iagrem of
a typical
this were not done it would be impossible to have the
otor operate efficiently under both starting and runconditions.
If the condenser was of the right
e for starting it would be too large for running,
while if the capacity of the condenser was suitable
for running under load it would be inadequate for
starting that &me load. The automatic switch is used
to control the value of the capacitance
under both
starting and running conditions.
In discussing the various elementa of capacitor motors one winding is referred to as Phase 1. or the main
winding, and the other is called Phaae 2, or the condenser winding.
This latter winding is sometimes
termed the starting winding. Perhaps a better way to
between the two windings would be to
refer to one as the main phase, and the other as the
condenser phase. In other words, the main phase is
the one connected across the line and the condenser
phase is the winding that counects to the line in series
with the condenser.
The two windings are identified
in Figure 2.
In the ordinary two-phase motor (arid aimilarly in
the case of the three-phase)
the currents
through the two separate windings are out of phase
with each other.
The magnetic waves of each phase
are some distance apart and reach maximum values
at different
instants giving the effect of a rotating
Fig. 4.
Diagram of a split-phase condenser
th windings are nearly equal in
rns .
. .
magnetic field that causes the rotor to revolve in the
That. briefly, is the theory of operasame direction.
tion of the two or three-phase
(polyphase) induction
motor, and accounts for its self-starting
On the other hand, single-phase motors are not selfstarting unless some special provision is introduced
to create a rotating magnetic field similar to that of
the polyphase motor just described.
A motor can be
provided with a single field winding and a squirrel
cage rotor that will deliver good power if the rotor is
brought nearly to running speed by an external means.
Such a motor, however, will not start itself and is
useless for most purposes.
Many methods have been devised to make singlephase motors self-starting.
Repulsion and repulsion
run are two methods in use but both
require a wound rotor brushes and other auxiliaries.
A simpler method utilizes the two-phase motor principle by diverting the single-phase current into two
paths, one path being through the main or running
winding, the other throu:h
a starting winding.
accomplished the desired result, that is, to cause the
current in one winding to lag behind the eurreut in
the other and produce the ro*&ting field necessary to
obtain self starting characteristics,
the starting wind126
iagram of a resistance split-phase
ng windings similar to a condenser
An out-of-phase current in the startwinding is produced by the resistance.
ing was designed with a resistance much greater than
that of the main or running winding.
Hundreds of thousands of this type of split-phase
motor, familiar
to nearly everyone in the service
field, have been manufactured.
To supply the necessary out-of-phase current relation, the starting winding was wound with many turns of fine wire and the
coils were placed at an angle-usually
between the
running coils. Since the starting coils were required
only for starting, and since they were prone to overheating if left in the ‘circuit for any appreciable
period, a centrifugual
switch was provided to disconnect the starting winding as soon as the rotor attained approximate running speed. A diagram of a
split-phase motor of this kind is shown in Figure 3.
h’ote the similiarity of this diagram to that of a plain
condenser split-phase motor as shown in Figure 4.
The essential difference
in the split-phase motor
shovm in Figure 3 and that illustrated
in Figure 4
is that in the former the higher resistance of the starting winding causes an out-of-phase relation between
the current in that winding and the current in the
main winding, while in the capacitor motor shown in
Figure 4 an external condenser connected in series
with the starting
winding causes a similar out-ofIn both cases, the difference in phase
phase relation.
between the currents in the two windings results in
the formation of a rotating magnetic field, the essential chara&eristic
of a self-starting
Although the starting winding of the ordinary splitphase motor usually consists of many turns of small
wire, the starting
winding of the capacitor motor
may have more or less turns than the main winding.
In many instances the size of wire will be the same
in both windings,
The relative size and number of
turns of the starting winding of the capacitor motor
will depend upon the t,ype of service for which the
motor is designed.
A forerunner
of the co:ndenser split-phase motor
was the type known as the resistance split-phase motcr. Here the two -windings were nearly equal in
weight and turns, as with the condenser motor, so
that the phase difference in the winding currents had1
This was,
to be brought about by some other means.
accomplished by inserting a resistance in the starting winding circuit.
This resistance
served about
the same function as the condenser does in tbe capacitor motor, but not as efficiently.
A diagram of a
resistance split-phase motor is shown in Figure 5.
The characteristics
of the condenser are most important factors in the starting and running efficiency
of the capacitor motor.
To obtain best results, the
capacitance value of the condenser should be large
when the motor is starting and should then be reduced
graduaiiy as the rotor speed increases.
The highest
efficiency could be obtained by varying the capacitance to suit each change in the load, but this would
require a comp!icated system of taps and switches.
the other hand, the use of a fixed condenser suitable
for the running period will only provide about 50%’
of the running torque for sta,rting purposes.
In a
great many applications
this torque would be sufficient for starting, and some means for increasing and
decreasing the capacitance for starting and running
mu&. be used.
ig, 6. Condenser motor with windings similar to a resistance split-phase motor. The
condenser produces the out-of-phase current
relation which gives the advantages of twophase operation.
If a single condenser is used, connected to the starting winding by means of an automatic switch that
opens at running speeds, the result will be a motor of
the type commonly known as condenser start-induction run. A motor of this type does not approach the
To obtain a higher
usual two-phase motor efficiency.
efficiency, a double condenser is used In many motors
both sections being used for starting
and one for
This system gives the condenser mctor
similar to the two-phase motor, and a
large number of this type have been built.
Figure 6 shows a diagram of a typical motor of
this sort.
Two condensers are employed, one of which
is always in the circuit of the starting or condenser
The second condenser is conuected to this
same circuit during the starting period by means of
the centrifugal
switch, and is disconnected when the
motor reaches approximate running speed. Thus for
all practical purposes the motor is operating as a two
phase motor, through the medium of the first condenser, although energized from a single-phase
Fig. 7. An ideal but impractical design of a
eon~enser motor. Variable capacitance to
suit changing load conditions would increase
efficiency but at the expense of simplicity.
cuit. Both the running and tbe starting condenser
can be, and usually are, housed in the same container.
As mentioned previously, the efficiency and power
could be increased to a certain extent
if three, four or more condensers were suitably connected in the condenser winding circuit as indicated
in Figure 7. The advantage to be gained is rather
slight, and would be more than offset by the difficulty
of adjusting centrifugal switches to cut in and out in
t;le proper order during speed or load changes.
sinall measure of efficiency
is sacrificed, therefore
in the interests of simplification.
An auto transformer,
in addition to the condenseris used in some condenser motors,
The value of the
capacitance is fixed at all times and the variation to
suit starting and running conditions is obtained by
varying the voltage applied to the condenser terminals. The circuits of such a motor are shown in Figure 8. During the starting period a higher voltage
is applied to the condenser than that required for
The effect is about the same as though the
capacitance was changed, but the efficiency as a whole
is lowered because of the losses in the transformer.
Now that we have seen how the size of the conden130
condenser motor using e transBP to vary ea~aci~~nce.
ser affects the starting ability and power factor of
the capacitor motor, let u8 consider the motor windings. The ratio of turns in the two winding8 as well
a8 the weight of the copper has an important effect
on performance.
The starting torque of the n:otoi
can be influenced considerably by changing the ratio
of turns in the two windings.
The size of wire used, as well as the number of
t~urns, in the main winding are more or less definitely
established for a motor of any given output.
If the
number of turns in the main winding are too large
t.he pull-out torque will be too low for many u8e8. If
the number of turn8 in the main winding are too small
the efficiency and the power factor will be seriously
For thest: reasons the original
should be followed closely when rewinding the main
phase winding of a capacitor motor.
The design of the starting
or condenser wirtding
may be subjected to more variation
than the main
The size of wire and the number of turns
in this winding can be varied 80 a8 to obtain the apIf the numproximate starting performance desired.
ber of turns in the starting winding is doubled, the
wire size reduced to one half the former cro8s eection,
and the condenser
replaced with one about one.
fourth of the former value, the torque will be reduced
Fig. 9. A method of reversing direction of
fotatioR of a condenser motor
approximately fifty per cent. If a greater torque t.han
that originally available from the motor is required,
the starting winding should be rewound with fewer
turns of larger wire than that formerly used and s
much larger condenser should be used.
Condenser motors are reversible but, the change can
only be made externally when the manufacturer
provided the proper taps or terminal8 for this purpose.
Other types must be opened and the internal connections adjusted to obtain a change in rotation.
Figure 9 show8 one method of reversing an ordinary capacitor motor by mean8 of a switch mounted on or
X single pole, double throw switch
near the motor.
connected as shown will allow t.he motor to be operated in either a foward or reverse direction.
Since the condenser is such an important factor in
the, operation of the capacitor motor it might be advisable to dl8lTIS8 the types in use and their construction. Both paper and electrolytic condensers are used
with capacitor motors, one of each kind being used
on some motors.
Where t,his is the case the elect,roiytic condenser is used in the starting circuit, and t,hc
Fig. 10. Comparison chart of condenser, no~uision-induction, and split- ase motorsof
% hp size
paper o-le in the running circuit.
Paper condensers able to stand the strain of starting the motor are made but have found little us& for
this pnrpose.
The paper type, or dry, condenser ha8
the advan+&ge of high efficiency but at the same time
ha8 two serious disadvantages
from a practical standpoint.
One i8 the initial cost of cOndell8er8 of the
size nsually required for starting, and the other is
the matter of bulk. The opposite is true of the electrolytic type. It is small in size for it8 capacity, the
cost is low, but internal losses are high.
Since the use of a condenser in the starting circuit i8
losses are
In a test conducted by one of the well known testing laboratories
on the relative merits of the condenser, the repulsion-induction,
and split-phase type
motors, the general results shown in Figure 10 were
Each of the motors used in the test was one
e be& and most efficient types available comarcially, and all were of t,hc popular one quarter
er size.
SIDE from burned out windings, worn bearings and rough commutators, one of the main
causes of having motors brought to the shop
is that of having the direction of rotation reserved.
Such a task, no matter how simple it may be for the
service man, is usually a great mystery to the customer.
In most cases the owner of the motor has
picked it up to operate some piece of machinery and
finds out later that it does not turn in the right
direction to suit his need.
A case of this kind happened last winter. The engineer aboard a fair sized yacht was instructed
by the
owner to install some sort of a ventilating
system to
rid the living quarters
of the boat of the cooking
odors and heat from the ship’s galley. Instead of ordering an electric motor powered blower made for
d lines
Fig. 2. Changes necessary to reverse rotation of a
shunt wound motor are shown by outline marks
the purpose, the engineer, thinking himself to be an
expert electrician,
shopped around among the electrical stores and purchased a ?i H. P. motor and a set
of fan blades. With the aid of a tinner he rigged up
an exhaust flue through the deck and installed the
improvised blower close by the galley range.
Several days later when the yacht was forty miles
down the coast the engineer, prompted 110 doubt by
the irate owner, put through a long listance call to
the shop where he had purchased the motor. It seemed
that this ventilating
system worked in a reverse manner from what had been expected of it, and instead
of carrying away the heat and fumes from the galley
to the outside air, it was filling the space below
the decks with the smell of frying fish and British
Thermal Units from the galley range. The main theme
of the conversation
was that they wanted a service
man to reverse the motor, and they wanted him quick.
The outcome of this little incident, as far as the
shop was concerned, was that the electrician
sent on
the job collected a twenty dollar bill for his time and
expenses for doing what would have ordinarily
a one dollar job. And to show that he was a good
defections of a split-phase motor. To
. 3.
change rotation reverse either terminals 1 and 4
or 2 and 3 in relation to power line
as well as an electrician,
he sold the
owner two factory built blowers, one for the galley
one for the engine room, to be installed as soon
as they arrived.
Most motors are easy to reverse if the principles
involved are understood.
Different methods must be
used to reverse the rotation of the various types of
motors, and a small amount of space will be given
here covering the types in most popular use.
First to be considered will be direct-current
of the types in general use, as the same instructions
will do for 6, 12, 32 and 110 volt machines.
Direct current motors are reversed by reversing
the direction of current flow through either the field
or the armature,
but not both.
The circuit of an
ordinary d-c motor of the series type is shown in Figure 1, and that of a shunt connected motor in Figure
2. As it is usually easier to change the field leads at
the brush holders, thus reversing the path of the
current through the armature, this is the means most
often employed.
In the diagrams, the original connections to the brushes are shown as solid lines,
while the changes made to reverse the rotation of
the armature
are indicated
by broken lines. It is
sometimes necessary to lengthen either one or both
of the field leads in order to reach the desired brush
holders, or to keep the wires from passing too close
to the commutator.
On the smaller d-c machines,
and those having
eitber solid end bells or ones with small inspection
holes, it will be necessary to remove the commutator
end housing to accomplish the job of reversal. In any
case this is usually a small matter and the entire job
can generally be completed in a half hour at most.
Small universal motors-a-c
or d-c--are reversed in
the same manner as the series direct-current
current motors are reversed in several
different ways, depending upon the type of motor under consideration.
In the case of the common splitphase motor we must get at the junctions
of the
windings in order to change the direction of rotation,
and this means partly dismantling
the motor.
The split-phase
motor has two distinct windings,
the heavy low resistance
winding, and a
smaller high resistance starting winding. To change
the direction of rotation of the rotor the terminals of
either one of the windings must be interchanged.
That is, the line terminals
of the running winding
can be switched in relation to the line, or the two
ends of the starting winding can be shifted on the
line. Do not make the mistake of changing the terminals of both windings or no change of rotation will
result; leave one winding as it was found.
Figure 3 shows a schematic
diagram of a splitphase motor winding. The points marked 1, 2, 3 and
4 are the connections of the two windings to the line.
To change rotation
1 and 4, or interchange 2 and 3, but never all four points.
motors are perhaps as a class
the easiest on which to change rotation.
Having ,a
wound rotor, a commutator and set of brushes and
brush holders similar to d-c machines-save
that the
brushes are shorted together through the metal of
the brush rigging-makes
a change in direction mechanically simple.
Motors of this type are provided
with an external means of shifting the brush holder
a certain number of degrees either side of the neutral.
Narrow slots, known as index marks, are cut
into the metal of the end bracket in the proper positions for clock-wise
or anti-clockwise
Another mark or pointer on the brush rigging can be
made to coincide with one of these marks.
Fig. 4. Reversing robtion of a repulsion start-induction run motor. Shifting index pointer to other
index mark changes rotation
form of lock scr~ew or clamp is usually provided to
prevent shifting, and this must be released before
making a change in the setting.
Figure 4 shows the commutator end of a motor of
this type in which the index marks, pointer and lock
screw are plainly seen. These factory markings can
not always be relied upon if a motor has been rewound or has had a new commutator
slight change in the winding or position of the commutator on the shaft will cause a shift of the true
neutral position of the brushes-a
point at which the
armature will revolve in neither direction-and
-consequently will likewise shift the brush positions for
best pperating conditions.
By means of instruments
on a test bench, or by means of a starting torque test,
the position of the brushes for greatest efficiency in
starting can readily be located. New marks can then
be made on the motor frame.
It is sometimes desirable to have a reversible motor
on such a piece of machinery as a lathe, when the expense of purchasing
a tru,e reversing motor ie un-
For occasional work of this kind at constant speed, a repulsion-induction
motor can be
adapted. By bolting stbps at each end of the index
marks, some form of hand control can be attached to
the index pointer, so that a quick shift can be made
for rotation in either direction. This type of motor
must, however, be allowed to come to a full stop before attempting to run it in the reverse direction. or
serious burning or arcing at the commutator
Straight induction
motors are easily reversed in
moat cases by exchanging the end bells so that the
rotor can be changed end for end. As a rule motors
of this type are built so that either end housing will
bolt to either side of the stator housing.
By switching the rotor end for end, or by leaving the rotor as
it is and turning the stator around, the rotation of the
machine will be reversed without any alteration
the windings or connections.
Figure 5 shows this
Shading-coil motors can not be reversed by changing leads or terminals,
as this type of motor, used
mainly in ceiling fans, has but one winding connected to the line. The shading-coils,
which are used to
make this form of motor self-starting,
are placed to
one side of the main poles, and would have to be
shifted to the opposite side of the main poles to cause
a reversal of the direction of rotation.
In most cases
this would be a practical impossibility,
as it would
necessitate a complete rebuilding of the field, and is
a method hardly ever used.
The shading or starting coils used in these motors
consists of either a circular copper band, or of a
short circuited coil of heavy wire. This band or coil
inserted in the trailing edge of the pole retards the
flow of the magnetic flux in this side of the pole and
causes a phase displacement
which has a rotating
effect on the rotor.
These starting
coils are insulated from the main winding.
Fig. 6.
To change the rotation of a shading-coil motor, reverse the end bells and rotor in relation to the field.
If this is impossible because of mechanical
restrictions, it may be possible to press out the stator lami140
r c~curm
nations with the windings intact, and press it back
into place in a reversed position.
In the latter case
the rotor, of course, must be left in the original posL
tion in the frame.
After rewinding the stator of an induction motor,
or before assembling
the complete machine,
it is
often desirable or essential to know in which direction the motor will operate.
This information
be determined in advance with the use of a simple
shop made tool which, for want of a better name, can
be called a “testing rotor.”
Figure 7 shows such a device, and a description of
its construction
will be given here.
The material
needed to construct a testing rotor consists of two
discs of fibre, bakelite or hard rubber, and a few feet
of bare copper wire in several sizes. This material
is formed into the shape of a squirrel cage, with two
coils projecting from the ends. The cage is mounted
on an axle which also forms the handle by which it
is held when in use. Figure ‘7 gives the approximate
dimensions of the tool,
Fig. 5. To reverse rotation of an induction motor
change rotor end for end, or change sides of stator,
but not both
To discover the direction in which the assembled
motor will rotate, connect the stator windings to the
line, and with normal current flowing through the
coils, hold the testing rotor inside of the stator opening close to the core. Observe the direction in which
it tends to turn, This direction will be the same as
the rotation of the assembled motor.
Another handy testing device for the motor repair
or rewinding shop is an internal growler. Just as an
ordinary growler detects faults in most armatures, so
will the internal growler locate short circuits inside
the field ring or stator.
Such a piece of equipment
as just mentioned
can be made at little or no esy142
pense by any electrician,
and will be well worth the
time and material expended on it.
Figure 8 shows a detailed drawing of the internal
growler and the manner in which it is used. In reality
this tool is a core t.ype transformer
having but one
winding, the primary. The primary coil is excited by
110 volt a-c current as the growler is passed around
inside of the stator.
The laminated iron core of the
internal growler, shaped to fit the inside of a circle,
creates an alternating
magnetic field, and the stator
coils in the path of this alternating
field become for
the moment the secondary
winding of the testing
When the internal growler is moved around the inside of the stator-touching
the stator iron--end
passes over a short circuited turn or coil, the result is
the same as when the secondary of a conventional
is short circuited. The short circuiting of
the secondary causes an increased flow in the psimary of the transformer,
and this increase of primary current can be detected by having an ammeter
in series on the 110 volt line. At the same time that an
increase in current flow is registered on the ammeter, it usually happens that considerable
heat is generated in the short circuited section of the secondary
of the stator.
After a moment or two the defective
turn or coil of the st.ator can be located by feeling
over the surface just tested with the bare hand.
Another method of finding shorted coils with the
internal growler is as follows : Just as a shorted armature in an armature growler will cause attraction
for a strip of metal-such
as a hacksaw blade-held
above the defective coil, so will the shorted stator
coil hold an attraction for a strip of steel. In making
this test the steel strip must be held to one aide of
the growler so that it will cover one side of the coil
while the growler is covering the other side. Thus tht
growler and the steel strip must De over
sides of the same coil while making
the test, and both must be moved around while maintaining their relative positions.
The laminated core of the internal growler can be
made from a section of the core from a small direct143
current a ature by cutting off some of the legs, or
it can be shaped from the laminations
of some power
such as is used in radio work. Flexible
leads should be provided, and it is well to have an
on and off switch fitted to the handle
of the tester.
Grounded windings can also be tested
with this device by proceeding as follows :
To test for grounds in a stator winding, place the
internal growler inside the opening and touch each
at&or lead to the stator frame. If a spark occurs that
If the stator coils are not as yet
circuit is grounded.
connected together, or where is more than one
winding, each coil lead or winding lead must be
tested separately.
If a ground is discovered in one or more of the
stator windings, the exact slot in which the ground
is located can be found in the following manner:
Ground. ,one end of the defective coil or winding securely to the stator frame.
Next make the growlet
and hacksaw blade test around the inside of the stator. The slot over which the hacksaw blade vibrates
is the one in which the ground is located.
owler is a great time an
An internal
r shop. Lige many other “
aaver for the m
it is
1 worth the labor and thought
I it.
ler for ~0cJ~~~
t-man has to contend with
m time to time, as well as
the ~~rneroMa troubles that can be traced directly to improper brush functionin
. Altogether too
y people have the idea that a brush is just a brush,
that all that is necessary is to roughly fit any
handy piece of carbon and insert it in the brush holder.
The result ie that a large number of motors
ller aisee, are continually comi
shop with co
even worn completely through.
The material from which brushes are made can
be classified as follows: Pure carbon brushes,
brushes, graphite
brushes, e
aphite brushes, and brushes
made from
raphite ~om~oaitiou~ The physical properties of these
teriale or compositions must be taken into account
when selecting brushes for a given job.
The resistance of the brush material ia a very important factor in many applications.
The specific res~tance of brush material is its resistance in ohms
per cubic inch. In the laboratory this is measured by
ing a brush one inch square and takin
meaa~reme~ta from opposite sides. If the
of the material is too great for the work the brush
must do, the brush will heat up in service.
The second important factor in brush design is current carrying capacity.
A brush should be able to
rry its rated ampere load without causing the operding ~mperature
to rise more than 60’ Centrigrade
under usual conditions.
The carrying capacity of
ed by both the specific resistance of
which it is made, and by the area in
with the commutator and holder.
e ~eri~heral speed of the commutator also has a
brush selection.
The h
the greater the need for hl
d also, the need for better lubrica-
tion of the brush.
Carbon or carbon-graphite
are best suited to slow or medium speed equipment
where the carrying capacities are not too high.
brushes are adapted to high peripheral
speeds and where commutating
be of the best. Electra-graphitic
brushes are nonabra,sive and are best fitted for use on undercut commutators, or where commutator
slot insulation
e an abrasive brush.
te brushes are very soft and meet the requireery high operating speeds as weU as where
ities must be unusually high.
current carrying
w rule, commutat
t be undercut for graphite
b~~~~es~ for the reason that the brush material is too
soft to keep the slot insulation worn down even with
etal-graphite brushes find
aa at~rti~g motors of vrrious types, and are also
on ~~ter~ting~urre~t
slip ring motors and generators.
brasiveness of a brush does not necessariiy
dep~?~d on the hardness of its material.
A soft grade
y be very abrasive, while a hard
another type will cauee but little commutator
ount of abrasiveness in a brush i*
ep both the surface of the brush face and
of the commu~tor clean and polished.
The abrasiveness of any brush is also influenced by the peripheral
sped of the commutator, and by the preseure applied,
by the brush sprin
The contact drop, or loss of voltage between the fad:e
of the brush and the surface of the commutat,or, drpends on the brush material, speed and pressure.
contact drop of almost any brush can be decreased b>
increasing the spring pre.?sure, but as this is done
brush frietion is increased.
An increase of brush friction may cause serious heating and undue commutator wear.
Where ihe contact drop of a brush is excessive it nould be better to change to a less resistant
brush, than to exert more pressure.
reasure is usually measured in terms of
square inch of brush contacting surface,
ed before, should be adjusted to a value
. 1.
where a compromise is effected between excessive contact drop and excessive brush friction.
A safe rule to
follow is to us the lowest brush pressure possible witbout sparking.
This will very seldom be less than 1%
pounds per square inch of brush contact surface except
with very aoft graphite brushes, where it may be
slightly less.
The motor repairman is seldom able to accurately
determine the hardness, abrasiveness,
drop of brush material, but ha is able to meascon
ure the brush pressure on the commutator.
This is
one with a brush spring tension scale, as shown
ure 1. The hook of the scale is slipped under
the outer end of the brush spring and the scale is pulled
away from the.brush at an angle that would cut through
the center of the commutator.
The brush arm or
spring should barely be raised from the brush when
the reading is taken direct in ounces and pounds from
tire body of the scale. The exact area of the brush surface must be calculated in square inches.
Brushes form such an important part in motor reir service work that every motor shop should mainn a reasonable stock of brushes designed for the
more popular types of motors.
These brushes, espe148
cially for the fractional
horsepower motors, are not
expensive and a representative
stock can be put in for
26. Because of the many pbyaical properties of
different brush materials, and because the nature of
the service differs in different types of motors, it goes
ying that the dealer’s brush stock should
the motor manufacturer
or from one of the
several reputable factories specializing in the making
of well engineered brushes for replacement purposes.
It is impossible for even the large motor shop to
ock brushes for every make and model of motor that
ay come in for service.
The time element is often
portance and it is not always possible to
a new sat of brushes and get them in time to suit
For this reason every motor
the owner of the motor.
shop should also stock a few sizes of sheet brush carbon.
Carbon sheets of a universal or general purpose
grade are available, and usually come in a 4” x 6” or
assortment of thicknesses fr
4” x 8” size, and in
to 1” or more.
und or square carbon rods of
eters in one foot len
a can also be bought, and
solve the problem of making odd brushes for very
small motors, such as are used on fans. drink mixers,
etc. With this material at hand any sort of brush can
and, while it may not be the exact
be cut and sba
type of brush needed, at least a set can be made to
“pinch hit” until the proper grade can be obtained.
With a little work the motor repairman can make up
brushes with shunts-often
called “pi
the are required.
The duty of a shunt,
of course, is to cr,rry the currenf directly from the
proper motor lead to the brush, or vice versa as the case
may be. In this way the brush holder, the brush
spring or the brush spring arm is relieved as an electrical conductor, and a much better circuit is aseured.
Shunts are attached to brushes in four ways: They are
moulded in place when the brush is made; they are
fastened in a hole drilled in the brush by means of a
scr’ew or pin; they are bolted in place, or they are cemented into a bole drilled in the brush.
Fig. 2.
The first way is out of the question for the average
repair shop, and the second method is delicate and
subject to considerable breakage.
It is easy enough to
bolt shunts to brushes, but except in the larger sizes
there is no room for this type of connection either on
the brush or in the confines of the brush holder. Therefore the most practical method for the average shop to
follow in fitting shunts to shop made brushes is to cement them in place. Both shunts and shunt cement
can be purchased from several of the large brush manufacturing concerns.
In addition to shunts, many of the brushes used on
large motors are equipped with hammer or lifting
slips. The hammer plate on a brush is a means of preventing fracture of the brush material,, or excessive
hollowing due to the action of the brush spring arm,
grinding on the top of the brush.
Lifting clips, as the
name implies, are used in applications
where the
brushes are automatically
lifted from the commutator
at certain times.
Some brushes are fitted with a shunt
and a combination hammer and lifting plate. When the
need for a set of brushes of this type is imperative,
the hammer or lifting clips from the old brushes can
be salvaged and reriveted to the new brushes. Fig. 2.
the right type of brush is a very important
ante, but no more so than prop
hation and adjustment.
This applies with
ell as large motors. To prevent
excessive wear and chattering,
every brush
be sanded to fit the curvature of the commu. This is easily done on many motors by cuttin
a striip of 00 sandpaper and banding it around the commutator before the brushes are placed. The sandpaper
must be wound around the commutator in a direction
that will cause it to tighten when the armature is
turned in its normal direction of rotation.
fine wire or rubber bands will hold the sandpaper in
place while installing
the brushes.
The armature
then be revolved until the brushes are well
Figure 3 shows a brush before and after
It is often impractical to sand in brushes on very
tore by this method.
However, round or
ushes used in miniature
motors should always be fitted to the curve of the commutator, as this
cheaply built equipment can stand less arcing as a
general rule than can more substantially
built moto
r fitting of small brushes can be accomplish
Install new brushes and operate motor for a minute
or so. Remove brushes and inspect the contact surface. The glazed part indicatea the section of the Burface tha,t is rubbing on the commutator.
Wrap a piece
of fine sandpaper around an object approximatey
same diameter as the motor commutator.
Rub the end
of the brush on this so as to grind away the glazed
Reinsert brush in motor and run motor for
another minute, then inspect.
Keep grinding
lazed portions of the brush until a test shows that
at least 76% of the contact surface is bearing on the
On vertical commutatore the brushes may be sanded
with a flat strip of fine sandpaper drawn back and
forth under the brush. Where the brush holder is attached to the armature shaft and is free to rotate the
brushes can all be sanded at once if a circular disk is
placed against the commutator face before the brush
holder and brushes are installed.
After the sanding
operation the paper can be tom out. This of
done with the armature out of the machine.
the sanding of the brushes is done inside the assembled motor or generator, care must he used to blow out
all the accumulated carbon dust from the operation.
Motors or generators having adjustable brush holdera, and where brush troubles are experienced, should
be checked for the angle at which the brushes are set.
The proper setting depends to a great extent upon
whether the armature rotation is against the heel or
the toe of lhe brush.
If the brushes are set for a leading position the angle, as a general rule, should be in
the immediate neighborhood of 36’. If the brushes
are in a trailing position the angle may vary from
10 to So. Trailing, leading and radial positions of a
brush are shown in Figure 4.
Brush spacing around the commutator is a source
of trouble on certain critical motors and generators.
Incorrect spacing is usually caused by careless assembly after a repair job, and ahowa up worst on inter-pole machines.
An easy way to check for correct
is to wind a strip of paper around the
nd then mark off the poeition of each
en the paper ie removed the distance be152
tween br~~bea is easily measured.
~~MsM~~s~a~~i~~ of the brushes is always an indition of trouble and can most often be traced to one
more of the fo~lowin
h mica between commutator bars; weak spring
incorrect spacing of brushes; oil and dirt
on ~omm~ta~~; flat spots or commutator out of round;
wrong type of brushes; brushes off the neutral; defective field or armature coils; brushes spanning too
; brushes tight or gummed in holders:
many b
ving too low a contact drop; brushes chattering; overload of machine ; worn armature bearings ;
air gaps at poles; vibration
of the motor;
loose or out of line brush holder studs; loose connections inside motor or at brushes.
3 ~e~~~ers and electri
I repair men, we
tly coneemed with the subject of ins
. Without insulation
in some form or
other we would have very few pieces of electrical
e~~~~rne~t that would operate.
Glass, porcelain, rubb&elite, cotton and other textiles, asbestos, mica
many other substances have played an important
e development of the electrical industry. In
the ease of motors and generators, however, the various types of insulating
used play a most
important, if not the most important, part in the construction and serviceability
of such machines.
varnishes are not only good insulator8 in
themselves but they also serve to protect the insulating properties of many other insulating
materials. If
the average electric motor were not protected by a
coat of good insulating
varnish, the action of vibration, heat, water, oil, dirt a,nd acid fumes
--any one or all of them-would
a complete failure of field or rotor circuits.
ithout a coating of insulating varnish, slot papers would soon bee brittle and crack or soggy from moisture, cotcoverings would fray or unravel, and the enamel
eQve~i~g of wires would chip and flake. When prop
erly applied and treated, insulating
varnish provides
film protective covering.
@cause insulating varnishes are used in relatively
small quantities
as compared with other motor rematerials, and because a knowledge of these
s involve principals of chemistry rather than
its, many armature
shop owners
ployeea do not have a clear understanding
why some varnishes
are best for one purpose and
others for another use. While the average rewinder
will not de interested in the chemical theory of ineuarniebes, a brief diecusaton of the different
nd their principal uses should be of interest.
f:lrm of insulating varnish is familiar
ly everyone under the common name of shellac. Shellac, and other allied gums and resins, diasolved in a suitable solvent ux~ally alcohol-form
the group known as spirit varnishes.
In these spirit
varnishes, the solvent evaporates
and leaves behind
a film of the gum or resin. The insulating properties
of this film depend upon the type of gum cr resin
used in the solution.
Since many of the gums used in
a~rni~bes are oil proof, we find them bein
ae a flna? and oil proofing co
the spirit va,rnish is usually very
d brittle and is subject to chipping and peelunded of nothing but a gum, the
non-drying oil, they have but littoughness and elasticity needed
for a good ~ns~Iating job. Because of their inherent
tendency to crack, spirit varnishes do not offer good
protection against water or atmospheric moisture.
The most successful varnishes
for the impregnating of windings
are tbe oil type varnishes.
group, tecbni~a~~y known as oleoresinous
are composed of a gum or resin, vegetable drying oils
and a suitable thinner.
In the manufacture
if varnishes of this type, the gum and oils are given a
special heat treatment
at high temperatures,
which the thinner is added to the mixture.
Oil type varnishes
dry in an entirely
anner from tire spirit varnishes.
The thinner used,
being volatile, evaporates
mit,hin a few hours and
leaves a coating of the heat treated gum and oils on
the surface of the work. In speaking here of the
beat treatment
of the gum and oils, we are not referring to the baking process done on the finished
but to the process employed in the making
of the varnish.
The purpose of the thinner in this
of varnish is to act as a vehicle for the spreadof the gums and oils into thin films.
It has no
other effect upon the final characteristics
of the
The evaporation
of the thinner
is only the first
in the drying of varnishes of this type. The reing gums and oils, still in a moist state, then
ergo chemical changes which in a certain period
of time will cause t~hem to solidify and harden.
cation of heat at this point produces a much
rapid action and, in most varnishes, produces a
more desirable and durable film. Some varnishes of
this type are air drying, but the baking types are
usually better and find a much more general use in
the manufacture
and repair of electrical machinery.
The oil type varnishes are much more elastic, durable and water resisting, and are best suited to the
~~su~atio~ of field coils and armatures.
The oil type varnishes
are made in four general
types known to the trade aa clear air dryin
ping, clear baking and black baking. Clear cold resins are used in the manufacture
e va~ishes~ while various asphaltic mathe base of the black varnishes. Suitable
oils and solvents are used with both the clear and the
black, the different physical properties of the finished product depending upon the kind of gums used.
for the
ile there are numeroue varnishes on the market
as general purpose varnishes, it is also true that
oseib~e to make a varnish that will give the
esults for all purposes.
For the small shop,
where the volu e of work is limited, it is impossible,
ry a special varuish for each type of
d a compromise must be reached by using one
af the genera purpose varnishes. The fact remains,
however, that better service can be expected by using
e of varnish best suited to each particular type
be weldings of a
urea call for
king period.
severe vibration will
aving a. semi-plastic
motor operating under very high
a varnish of a type that requires
Windings that are subjected to
hold up longer with a varnish
nature and a shorter
isb of this
type, however,
will not have
imum in oil proofing qualities. Emergency
ork on the other hand, will often call for one
air drying varnishes since the quality of
the insulation is sometimes of less importance than
the time factor.
aking and air drying varnishes differ in the
ratio of oil to gum, and also in the pxcentage
drier used. As a general rule, the air drying varnishes carry a smaller amount of the drying oils
than do the baking types. The main difference
between the clear and the black varnishes is in the
physical properties only ; the electrical properties
being about the same in both cases. Usually, the
hard drying varnishes are oil proof while the softer, ~~~~~b~~varnishes have poor oil proofing qualitiC3.
Even more important than using the right type
of ~~s~~ati~g varnish is the importance of applying the varnish in the right way. As already pointed out, insulating varnishes
are chemiaal compounds and like most chemical compounds they
are unstable under adverse conditions. Temperature, foreign matter and the addition of wrong
solvepts or thinners may make a tank of varnish
t for use. Considerable care should be used in
the handling of varnishes in the shop. When a
dipping tank is used, it should ‘be provided with
a tight cover, with a drain plug in the bottom and
with a drain board. See Figure 1.
can be
ip, in a spray gun, or they can be applied
duping is the best method for all small
one with which small motor winders are
ed. The big advantage of dipping lice in
the varnish is able to penetrate and satrts of the winding.
g the coils in the insulating varnish,
uld be preheated in the bake oven for a.
to four hours at a temperature
of apo F. This accomplishes a double pur157
Fig. 1. This dipping
tank with
will serve the small motor shop adequately.
The lid
should fit tightly and a valve should he provided for
drawing off the liquid for cleaning.
The size of the
tank will be determined,
of course. by the size of
the work handled.
pose; it dries out atmoFphrric
moisture on thr one
hand while on the other it brings
the core and windings up to a temperat.urr that will readily thin the
insulating varnish and allow it to flow freely into the
slots and recesses. The dipping tank should contain
a sufficient quantity
of the varnish to prevent the
varnish temperature
from rising more than a few degrees when the hot armature or stator is immersed.
ing an
The length of time allowed for the dip depends
The be& rule to
entirely upon the type of work.
follow is to leave the work in the tank until all bubbling ceases, but a much longer period will do no
After the dip comes the draining, and for
reasons cf economy the draining should be complete.
en baking
coils or armatures,
they should be
placed in the oven in an upside down posit,ion from
that which they were drained.
Heat will cause some
flowing of the wet varnish and the reverse
position will make for a more even film.
The time allowed for air drying or for baking will
depend, of course, upon the individual specifications
of the varnish used. All types of work do not re-
heating units are conoven is piaced over
me tbiekness of the varnish film, and
ust be considered
when preparing
the dip.
rily, one coat of varnish is not enough to give
of high quality.
Two or more thin coats are
than one thick coat. This comes about
e fact that a thin varnish coat can be
more successfully oxidized or dried than can a thick
The cons~sten~y of most insulating
varnishes as
come from the can are too thick for general
and viscosity
0888, and the specific
must be reduced by means of a thinner.
unt that the varnish
must be reduced by the
tion of a thinner can ge found by experimentation or by using a suitable type of hyrdometer.
a hydrometer is one that is calibrated for measuring
liquids that are lighter than water.
Proper allowances must also be made for the temperature
of the
If the temperavar~isb when the reading is taken.
ture of the varnish is above or below a standard set
at, say 7W F., we add or subtract a correction factor
of .0004 for each degree above or below our standard.
Tke correction factor is added to the reading when
the liquid temperature
when the
is above the standard, and subvarnish
is colder than
The thinner for spirit varnishes
is alcohol.
good solvent for many of the commercial baking varnishes is procurable from many of the larger oil
companies under the name of “solvent” or “Light
The distillation
end point should be below 160° .3 and the density from 54” to 58 Baume.
be cost is about 15c to 2Oc per gallon.
and coal tar distillates
should not be used because
of their softening
action on the enameled coating
of wire.
During the mixing, the thinner and the
varnish should be of the same temperature
and tbe
inner should be added slowly and thoroughly
Curdling of the mixture is caused chiefly
by blending when either the varnish or the thinner
is too cold, by adding the thinner too rapidly, by
using the wrong thinner, or when the varnish has
become partially oxidized or stale.
Bake Ovens l~~orta~t
An efficient baking oven p!ays an important part
in turning out satisfactory
The oven should
provide a uniform dry heat, good ventilation,
and reliable temperature
thing to bear in mind is that a varnish
cannot be dried properly if allowed to bake in its
own solvent vapors. Ovens must. be equipped with
a ventilating
system that will not only carry away
the solvent fumes, but which will allow a constant
supply of fresh warm air to aid in oxidizing
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