Troubleshooting Guide
for N1225-1/N1237-1/N1505-1 Alternators
Hazard Definitions
These terms are used to bring attention to presence of hazards of
various risk levels or to important information concerning product
life.
Indicates presence of hazards CAUTION
that will or can cause minor personal
injury or property damage if ignored.
Indicates special instructions NOTICE
on installation, operation or maintenance that are important but not related to
personal injury hazards.
will be lower than the regulator setpoint and the system
amps will be high. This is a normal condition for the
charging system. The measured values of system volts
and amps will depend on the level of battery discharge. In
other words, the greater the battery discharge level, the
lower the system volts and higher the system amps will
be. The volt and amp readings will change, system volts
reading will increase up to regulator setpoint and the system amps will decrease to low level (depending on other
loads) as the batteries recover and become fully charged.
Table of Contents
• Low Amps: A minimum or lowest charging system
amp value required to maintain battery state of
charge, obtained when testing the charging system
with a fully charged battery and no other loads applied. This value will vary with battery type.
Battery Conditions
• Medium Amps: A system amps value which can
cause the battery temperature to rise above the
adequate charging temperature within 4-8 hours of
charge time. To prevent battery damage, the charge
amps should be reduced when battery temperature
rises. Check battery manufacturer’s recommendations for proper rates of charge amps.
Section 1: Wiring Diagram......................................... 2
Section 2: Basic Troubleshooting..............................3
Section 3: Advanced Troubleshooting................. 4 – 6
Until temperatures of electrical NOTICE
system components stabilize, these
conditions may be observed during cold start voltage tests.
• Maintenance/low maintenance battery:
— Immediately after engine starts, system volts are lower than regulator setpoint with medium amps.
— 3-5 minutes into charge cycle, higher system volts and reduced amps.
— 5-10 minutes into charge cycle, system volts are at, or nearly at, regulator setpoint, and amps are reduced to a minimum.
— Low maintenance battery has same charac-
teristics with slightly longer recharge times.
• Maintenance-free battery:
— Immediately after engine start, system volts are lower than regulator setpoint with low charging amps.
— 15-30 minutes into charge cycle, still low volts and low amps.
— 15-30 minutes into charge cycle, volts increase several tenths. Amps increase gradually, then quickly to medium to high amps.
— 20-35 minutes into charge cycle, volts increase to setpoint and amps decrease.
• High-cycle maintenance-free battery:
— These batteries respond better than standard maintenance-free. Charge acceptance of these batteries may display characteristics similar to maintenance batteries.
Charge Volt and Amp Values
The volt and amp levels are a function of the battery
state of charge. If batteries are in a state of discharge,
as after extended cranking time to start the engine, the
system volts, when measured after the engine is started
TG0017B
• High Amps: A system amps value which can cause
the battery temperature to rise above adequate charging temperature within 2-3 hours. To prevent battery
damage the charge amps should be reduced when
the battery temperature rises. Check battery manufacturer’s recommendations for proper rates
of charge amps.
• Battery Voltage: Steady-state voltage value as measured with battery in open circuit with no battery
load. This value relates to battery state of charge.
• Charge Voltage: A voltage value obtained when the
charging system is operating. This value will be higher
than battery voltage and must never exceed the regulator voltage setpoint.
• B+ Voltage: A voltage value obtained when measuring
voltage at battery positive terminal or alternator B+
terminal.
• Surface Charge: A higher than normal battery voltage occurring when the battery is removed from a
battery charger. The surface charge must be removed
to determine true battery voltage and state of charge.
• Significant Magnetism: A change in the strength or
intensity of a magnetic field present in the alternator rotor shaft when the field coil is energized. The
magnetic field strength when the field coil is energized
should feel stronger than when the field is not energized.
• Voltage Droop or Sag: A normal condition which
occurs when the load demand on the alternator is
greater than rated alternator output at given rotor
shaft RPM.
Page 1
Section 1: Wiring Diagram
CEN N1505-1, N1237-1, and N1225-1
Dual Voltage Alternators Description
and Operation
N1505-1 28 V 100 A and N1237-1/N1225-1 28 V
200 A alternators all with optional 28 V/14 V (50 A
maximum on 14 V) are internally rectified. All windings and current-transmitting components are nonmoving, so there are no brushes or slip rings to wear
out.
After engine is running, N3135 regulator receives
energize signal. Regulator monitors alternator rotation
and provides field current only when it detects alernator shaft rotating at suitable speed.
• can be used in single or dual voltage with these
alternators.
— Allows single-voltage operation (28 V only).
14 V is not available as a single voltage appli-
cation with this regulator.
— Provides optional 28 V/14 V output only from the regulator when phase cable from alterna-
tor is connected to regulator.
IGN terminal
AC terminal
B– terminal

AC
IGN


After regulator detects alternator rotation, it gradually
applies field current, preventing an abrupt mechanical load on accessory drive system. The soft start may
take up to 10 seconds at full electrical load.
N3135 regulator used with these units also
• is negative temperature compensated. Setpoints
are 28.0 ± 0.2 V and 14.0 ± 0.2 V at 75° F.
• maintains alternator output voltage at regulated
settings as vehicle electrical loads are switched
on and off.
28 V B+
terminal

14 V B+
terminal
14 V

• provides overvoltage cutout (OVCO). Regulator will
trip OVCO when system voltage rises above 32 V
in a 28 V system (16 V in a 14 V system) for longer
than 2 seconds. OVCO feature detects high voltage and reacts by signaling relay in F– alternator
circuit to open, turning off alternator. Restarting
engine resets OVCO circuit.
Figure 1 — N1505-1/N1237-1/N1225-1 Alternators and
N3135 Regulator Terminals
Figure 2 — N1505-1/N1237-1/N1225-1 Alternators with N3135 Regulator Wiring Diagram
Page 2
TG0017B
Section 2: Basic Troubleshooting
A.Tools and Equipment for Job
• Digital Multimeter (DMM)
• Ammeter (digital, inductive)
• Jumper wires
B. Identification Record
List the following for proper troubleshooting:

Alternator model number_______________________

Regulator model number ______________________

Setpoint listed on regulator______________________
C. Preliminary Check-out
Check symptoms in Table 1 and correct if necessary.
TABLE 1 – System Conditions
ACTION
SYMPTOM
Low Voltage Output
High Voltage Output
No 28 V Output
No 14 V Output
Check: loose drive belt; low battery state of charge.
Check: current load on system
is greater than alternator
can produce.
Check:defective alternator
and/or regulator.
Check: wrong regulator.
Check: defective regulator.
Check: alternator.
Check: presence of energize
signal.
Check: battery voltage at alternator output terminal.
Check:defective alternator
and/or regulator.
Go to Chart 2, page 5.
D . Basic Troubleshooting
1.
Inspect charging system components Check connections at ground cables, positive cables, and regulator harness. Repair or replace any damaged component before troubleshooting.
2. Inspect connections of vehicle batteries
Connections must be clean and tight.
3.
Determine battery type, voltage and state
of charge
Batteries must be all the same type for system operation. If batteries are discharged, recharge
or replace batteries as necessary. Electrical system cannot be properly tested unless batter-
ies are charged 95% or higher. See page 1 for details. Nominal battery voltage for 28 V systems is 25.2 ± 0.2 V; for 14 V systems is 12.6 ± 0.2 V. TG0017B
Less than 25 V or 12.4 V indicates no charge condition when engine is running.
4.
Connect meters to alternator
Connect red lead of DMM to alternator 28 V B+ terminal and black lead to alternator B– termi-
nal. Clamp inductive ammeter on 28 V B+ cable.
5. Operate vehicle
Observe charge voltage at batteries with engine running (nom. 27-28 V or 13.5-14.0 V).
If charge voltage is above
CAUTION
32 V for 28 V system or
16 V for 14 V system, immediately shut down system. Electrical system damage may occur if charg-
ing system is allowed to operate at excessive volt-
age. Go to Table 1 at left.
If voltage is at or below regulator setpoint, let charging system operate for several minutes to normalize operating temperature.
6.
Observe charge volts and amps in each circuit
Charge voltage should increase and charge amps should decrease. If charge voltage does not in- crease within ten minutes, continue to next step.
7. Batteries are considered fully charged if charge voltage is at regulator setpoint and charge amps remain at lowest value for 10 minutes.
8. If charging system is not performing properly, go to Chart 1, page 4.
9.
Check OVCO (overvoltage cutout) circuit.
Shut down vehicle and restart engine. If alternator functions normally after restart, a “no output condition” was normal response of voltage regulator to overvoltage condition. Inspect condition of electrical system, includ-
ing loose battery cables, both positive and negative. If battery disconnects from system, it could cause overvoltage condition in electrical system, causing OVCO circuit to trip.
If you have reset alternator once, and electrical system returns to normal charge voltage condi-
tion, there may have been a one time, overvolt-
age spike that caused OVCO circuit to trip.
If OVCO circuit repeats cutout a second time in short succession and shuts off alternator F– circuit, try third restart. If OVCO circuit repeats cutout go to Chart 3, page 6.
Page 3
Section 3: Advanced Troubleshooting
Chart 1 – No 28V Alternator Output – Test Charging Circuit
STATIC TEST – KEY ON, ENGINE OFF
Shut down vehicle and restart engine. Does alternator function normally after restart?
Yes
No

Regulator responded to overvoltage condition.
Go to Chart 3 on page 6 to troubleshoot OVCO.

Shut off engine. With key off, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?
Yes
No

Repair vehicle ignition circuit wiring as necessary. Continue test.


With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator
B– terminal. Does 28 V battery voltage exist?
No
Yes

Repair vehicle ignition circuit wiring as necessary. Continue test.


With key off, engine off: Remove alternator-to-regulator 4-pin harness from regulator. Test for battery voltage across sockets D and C in harness plug. Does 28 V battery voltage exist?
No
Yes

Alternator is defective.

With DMM, check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator
harness plug. Connect black lead to B+ terminal on alternator. Does meter show 1.8 to 2.2 ohms?
No
Yes

Connect jumper wire from socket A in regulator harness plug to B– terminal
on alternator. Spark will occur. Touch steel tool to shaft to detect significant
magnetism. Is shaft magnetized?
No


Yes
Alternator is defective.

Test phase signal into regulator (AC). Set meter to diode tester:
Connect red lead of DMM to socket C of regulator harness and
black lead to socket B. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL
(blocking).
Yes

Regulator is defective.
Page 4
No

Alternator is defective.
SOCKET CONNECTIONS
A
B C D F–
Phase Signal AC
B–
28 V B+
Figure 3 – Alternator-to-Regulator 4-Socket
Harness Plug
TG0017B
Section 3: Advanced Troubleshooting
(CONT’D)
Chart 2 – No 14 V Alternator Output – Test Circuit
Shut off engine. With key off, engine off: Test for battery voltage of 14 V output terminal
on regulator. Does +14 V battery voltage exist?
Yes
No

Repair vehicle wiring as necessary.

Set DMM to diode tester. Connect red lead of DMM
to socket C of regulator harness plug and black
lead to each phase pin in phase harness plug. Meter
should show voltage drop value.
Then reverse meter lead connections. Meter should
show OL (blocking).
Yes

Regulator is defective.
No

Alternator is defective.
SOCKET CONNECTIONS
A
B C D F–
Phase Signal AC
B–
28 V B+
Figure 4 – Alternator-to-Regulator 4-Socket Harness Plug
PIN CONNECTIONS
A
Phase P1
B Phase P2
C Phase P3
Figure 5 – Phase Connection 3-Pin Harness Plug
TG0017B
Page 5
Section 3: Advanced Troubleshooting
(CONT’D)
Chart 3 – OVCO Trip – Determine 28 V or 14 V
With meter red lead on 28 V B+ at battery and black lead on chassis ground, start engine.
Watch meter dial: Does meter read charge voltage above 29 V?
Yes
No

28 V side tripped OVCO circuit.
Go to Chart 3b.

14 V side tripped OVCO circuit.
Go to Chart 3a.
Chart 3a – No 14 V Alternator Output – Test OVCO Circuit
Unplug alternator-to-regulator 4-socket harness from regulator. At receptacle on regulator, connect red lead
from DMM to pin C. Connect black lead to B– terminal. Does resistance read OL (out of limits)?
Yes
No


Alternator is defective.
Replace regulator with known good regulator.
Run engine. Does OVCO trip?
Yes
No


Original regulator
is defective.
Alternator
is defective.
Chart 3b – No 28 V Alternator Output – Test OVCO Circuit
Unplug alternator-to-regulator 4-socket harness from regulator. Connect red lead from DMM to pin A in
plug. Connect black lead to pin D in plug. Does resistance read 1.8 ± 2.2 ohms?
Yes
No

Alternator is defective.

With red lead from DMM connected to pin A in plug, connect black lead to B– terminal. Does
resistance read OL (out of limits)?
Yes
No


Replace existing regulator with known good regulator.
Run engine. Does OVCO trip?
Yes
No


Alternator is defective.
Original regulator is
defective.
Alternator is defective.
SOCKET CONNECTIONS
A
B C D F–
Phase Signal AC
B–
28 V B+
Figure 6 – Alternator-to-Regulator 4-Socket Harness Plug
Page 6
TG0017B
Notes
TG0017B
Page 7
Notes
If you have questions about your alternator or any of these test procedures, or if you need to locate a Factory Authorized Service Distributor, please contact us at:
C. E. Niehoff & Co.• 2021 Lee Street • Evanston, IL 60202 USA
TEL: 800.643.4633 USA and Canada • TEL: 847.866.6030 outside USA and Canada • FAX: 847.492.1242
E-mail us at support@ceniehoff.com
Page 8
TG0017B
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