E5 / / 111

E5 / / 111
United States Patent [191
Saar et al.
Jul. 5, 1983
4,114,083 9/1978 Benham et a1. . "
4,118,661 10/1978 Siekierski .
[75] Inventors: David A. Saar, Timonium; Richard T.
Walter’ Baltlmore’ b°th of Md-
1438002 10/1968 Fed. Rep. of Germany ...... .. 320/46
[73] Assignee: Black 8: Decker Inc., Newark, Del.
[21] Appl. No.: 337,174
[PH-man, Examiner_wmiam M_ Shoop
Attorney, Agent, or Firm-R. B. ShererrHarold
22 Fl d
[ 1
Weinstein; E. D. Murphy
A method of fast charging batteries by means of precise
5 1982
Related US. Application Data
dcgsézitiuanon of Ser' No' 911’554’ May 31’ 1978’ aban
analysis of the pro?le of the variation with time of a
characteristic of the battery which is indicative of the
[51] Int. Cl.3 .......................................... .. H01M 10/44
variation in stored chemical energy as the battery is
charged. The method speci?cally comprises analyzing
US. Cl. . . . . . . .
. . . . . . . . . . . . . . . . . . .. 320/20; 320/ 39
the pro?le for the occurrence of a particular series of
Field Of Search ............................ .. 320/20, 22-24,
events preferably including one or more in?ection
320/39, 40, 43
points which precisely identify the point in time at
which the application of a fast charge rate should be
References cued
discontinued. Additional methods of analysis provide
for termination or control of the charging current upon
3,289,065. 11/1966 Dehmelt et al. ........ ......... .. 320/40
the Occurrence of other events Such as limiting values
3,424,969 1/1969 Barry .
3,660,748 5/1972 Clayton .
21"‘: et a1‘ """""""""""""" "
on time, voltage or voltage slope or a negative change
in the level of stored energy.
Apparatus for performing these methods comprises a
suitable power supply and a microcomputer for analyz
3:890:556 6/1975 Mening ct
' ' ' ' ' " 320/23
""""""" "
ing the pro?le and controlling the power supply.
Kosmin ............................... .. 320/40
4,034,279 7/1977 Nillson ................................ .. 320/20
64 Claims, 14 Drawing Figures
a I’
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Jul. 5, 1983
Sheet 1 of6
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Jul. 5, 1983
Sheet 2 of6
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Sheet 3 of6
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Sheet 4 of 6
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Jul. 5, 1983
Sheet 5 ofl6
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Jul. 5, 1983
Sheet 6 of 6
, 1
either of which causes gradual deterioration of the bat
tery and premature failure.
In part, the failures of the prior art have been due to
the inability to accurately indicate full battery charge;
this has been due either to the failure of the prior art to
This is a continuation of application Ser. No. 911,554
?led May 31, 1978 and now abandoned.
select the proper'mode of indication, or to the fact that,
even if a reasonably 'good indicator has been selected,
the charging requirements of a battery vary substan
The subject matter of the present application is re
lated to that disclosed in co-pending and commonly
tially with individual cell chemistry, with individual
cell history and with ambient temperature. Thus, even
an indication mode which is reasonably well selected
for a particular battery type may actually provide an
assigned US. patent application Ser. No. 337,296, co
accurate indication only for a few cells having ideal
filed on Jan. 5, 1982, entitled “Apparatus and Method
characteristics and only if the cells are charged under
for Charging Batteries,” which application is a continu
conditions of ambient temperature.
ation of US. patent application Ser. No. 911,268 ?led 5 proper
For example, a major category of previous fast charg
May 31, 1978, now abandoned.
ing systems has relied upon temperature cutoff to termi
nate the fast charge mode. However, these systems are
This invention pertains to battery chargers in general _
and speci?cally to a method and apparatus for charging
batteries which permits any battery to be brought to its
full state of charge at a very rapid rate and also at maxi
mum ef?ciency without danger of damage to the bat
tery or to the charger. This invention will be described
with particular reference to nickel-cadmium batteries
but it is also capable of charging many other types of
batteries in the optimum manner for each of those par
ticular batteries.
subject to several difficulties: they may damage the
batteries due to the constant repetition of high tempera
ture conditions, even in specially manufactured (and
expensive) cells which are theoretically designed to
accept high temperatures; such systems may not be safe
for use with defective cells; they actually do not charge
a battery to its full capacity, in high ambient tempera
ture conditions; the charge ef?ciency is low and the
systems are therefore wasteful; and in low ambient tem
perature, the battery may be driven to self-destruct by
Battery usage in various products, particularly for the
retail consumer, has increased tremendously in recent
years. However, batteries are still looked upon with
substantial ' disfavor by many consumers because so
much of their experience has been with primary cells
which are wasteful, which must be frequently replaced
and which can cause serious damage if leakage occurs.
Rechargeable batteries have recently become more
popular in various devices, but problems are still en
countered by the consumer. Frequently, he discovers
that his batteries have self-discharged and need recharg
ing at exactly the moment when he would like to use the
device, and recharging in most instances takes an incon
veniently long period of time.
One solution to this is to provide maintenance charg
ing systems in which the battery can be left on constant
charge between uses. Even this system is of no value if
the consumer fails to put the battery back on charge
after use; in addition, most maintenance charging sys
tems actually cause slow deterioration of the battery
with time.
The solution to all of the above problems would be
venting or possibly explosion.
Another major category of prior art fast charging
systems relies on voltage cutoff. However, in many
types of battery systems including nickel-cadmium, this
terminationmode is unreliable due to the large voltage
variation which can occur with‘temperature, or due to
cell history or individual cell characteristics. Thus, a
voltage cutoff system can destroy a battery through
venting. Except in unusual ideal conditions, it will
never properly charge a battery to its full capacity.
A third major category of prior art battery charging
termination is based on simple passage of time. How
ever, the accuracy of this system depends on the bat
tery, at the beginning of charge, having an assumed
state of charge. There is a very high likelihood that this
will not be the case and that the battery will be either
45 over or under charged.
Most other charging methods which have been used
to date are based on combinations of one or more of the
above techniques. While some problems can be avoided
by these combinations, at least some of them still exist.
Even the best fast charge systems require expensive cell
constructions; but the additional cost only serves to
delay the battery deterioration which is caused by the
charging system.
A more recent technique, illustrated by US. Pat. No. ‘
the provision of an adequate fast charging system which
would reliably bring the battery up to its full state of 55 4,052,656, seeks the point at which the slope of the
voltage-versus-time curve for a given battery is zero.
charge in the shortest possible time and without risk of
However, even this technique is subject to dif?culties; it
damage. While the prior art is replete with attempts to
may detect another point at which the voltage slope is
provide good fast charging systems, no satisfactory
zero but at which the battery is only partiallycharged;
system has yet been developed. Most fast charging
systems today require very special conditions, such as 60 in addition, even if it properly locates the zero slope
point which is close to full charge, this inherently over~
unusually expensive batteries which can accept the
charges the battery and will cause battery deterioration
output of the fast charge system. Even under these
due to heating.
special conditions, there remains a risk of serious dam
age to either the battery or to the charger.‘ In addition,
the present fast charge techniques do not properly
charge the batteries. Depending on the termination
mode used, all fast charge techniques of which we are
aware either overcharge or undercharge the battery,
All of the battery charging systems of which we are
presently aware embody one or another of the above
techniques and are subject to one or more of the above
listed defects. This is true despite the fact that most’
currently known battery chargers are designed to be
used with only one type of battery and, in general, with
only one selected number of battery cells of that partic
ular type. The concept of a battery charger which can
accurately and rapidly deliver full charge to a variety of
different batteries including different number of cells or
different types of battery couples is totally beyond the
present state of the battery charging art. ,
The overall object of the present invention is to over
come the dif?culties inherent in prior techniques of
battery charging and to provide a new and improved
be kept at its full state of charge without gradual battery
It is an additional object of this invention to provide
a novel and unique method of evaluating the state of
battery charge and of controlling the applied charge
current in response to such evaluation so as to permit
the battery to be brought to its full charge state at the
maximum possible rate and at maximum ef?ciency
without causing damage or deterioration of the battery,
such method also including safeguards to protect
against damage due to the introduction of a defective
cell or to the introduction of a cell which is already at
method of and apparatus for battery charging which
full charge.
fully charges batteries at’ a very rapid rate and at maxi
mum ef?ciency and without causing either fast or slow
become apparent as the description and illustration
deterioration of the battery.
A more speci?c object of this invention is the provi
sion of a method and apparatus for charging batteries
which accurately identi?es the moment when the bat
tery has reached full charge and which terminates
charging without either under or overcharging the
A further object of this invention is the provision of a
method and apparatus for fully charging different bat
teries including different numbers of cells at the maxi
mum possible rate and ef?ciency, from unknown start
ing conditions.
Another object of this invention is the provision of a
method and apparatus for fully charging different bat
teries comprising different chemical couples at the max
imum permissible rate and ef?ciency, from unknown
starting conditions.
Still another object of this invention is the provision
of a method and apparatus for rapidly bringing a battery
to its full state of charge and terminating the fast rate
charge at that point, this being accomplished without
regard to the actual voltage of the battery, individual
cell characteristics, individual charging history of the
particular battery, or the actual ambient temperature.
In another aspect, it is an object of this invention to
provide a universal method for rapidly charging various
types of batteries and to further provide an apparatus
which selects the proper sub-method required to rap
idly charge a battery of a particular type.
In a further aspect, an object of this invention is the
Further objects and advantages of this invention will
thereof proceed.
In general, the present invention comprises a method
of applying a charge current to a battery, monitoring
selected battery parameters during the charging, infer
ring from changes in these parameters an indication of
the true charge condition of the battery, and controlling
the applied charging energy so as to bring the battery to
its full charge condition as quickly as possible without
damaging the battery. In addition, the general method
of this invention provides for the identi?cation of un
usual conditions which may occur in some cases, and
which require charge termination to protect either the
battery or the charger; furthermore, this method pro
vides for the application of a topping charge in appro
priate ‘cases and for the application of a maintenance
charge to keep the battery at full charge, all of these
being accomplished without danger of damaging either
the batteryor the charger. All of these objectives are
accomplished regardless of the actual voltage of the
battery; despite wide variation in individual cell charac
teristics; despite previous harmful charging history in
the case of a particular battery; and despite wide varia
40 tions in the ambient temperature to which the battery
and/or the charger may be exposed.
In particular, the present invention is based on the
discovery that the electrochemical potential of a battery
exhibits speci?c types of nonlinear changes of its value
45 with respect to time as the battery is charged. The in
vention is further based on the discovery that the true
provision of an apparatus for applying charge current to
a battery and determining accurately the moment when
a battery has reached its full state of charge.
Still another object of this invention is the provision
of an improved method and apparatus for fast charging
batteries which recognizes accurately when a battery
has reached a full state of charge, which thereupon
terminates the fast charge mode, and which subse
charge state of the battery during charging may be
quently supplies a topping charge current to the battery
conversion from a high rate fast charge mode to a suit
able maintenance mode which prevents or compensates
for self-discharge of the battery. In other cases, proper
control of the battery charging sequence may involve a
combination of in?ection point determination with
to compensate for batteries which, due to a particular
charging history, may produce a false indication of full
state of charge.
Still another object of this invention is the provision
analyzed by noting in?ection points which occur as the
electrochemical potential changes with respect to time.
In the case of speci?c batteries, proper charging may
involve determining the occurrence of either one or
more of such in?ection points, or of determining a par
ticular sequence of ordered in?ection points. Control
ling the proper charge mode may then involve simple
of a method and apparatus for charging batteries which 60 other analyses of the variation of voltage with respect
identi?es intermediate states in the charging cycle of a
to time or of the actual voltage at a particular time. In
particular battery and adjusts the rate of charging cur
all of these cases, a signi?cant aspect of this invention is
rent applied so as to maintain the applied current at the
the determination of in?ection points in the curve
optimum level for rapid, ef?cient and non-destructive
I which represents the electrochemical potential of the
65v battery as a function of time.
An additional object of this invention is the provision
By way of illustration of the above general method,
of a method and apparatus for providing a non-destruc
tive maintenance charge mode by which a battery can
vthe following speci?cation describes appropriate varia
tions on the speci?c type of analysis which may be
performed to determine the in?ection points, and also
describes variations in the analysis ‘which may be neces
sary to accommodate differing modes of battery charg
ing such as constant voltage, constant current, etc. Spe
In the course of recharging a nickel-cadmium battery,
it has been found that a very typical curve is produced
if the increasing battery voltage is plotted as function of
ci?c applications‘include techniques for charging such
time. FIG. 1 is a representation of a typical curve of this
type, as taken during a constant current charging cycle.
A similarly typical curve can be obtained by plotting
batteries as nickel-cadmium, lead acid, and silver-cad
In further accordance with the present invention,
current against time during a constant voltage charging
apparatus is described for implementing these various
cycle, and a reproducible pattern also occurs if neither
methods. In a preferred embodiment, the apparatus
voltage nor current are held constant This curve may be
includes a suitable source of electrical‘ energy, an analyt
divided into signi?cant regions, as indicated by the
Roman numerals between the vertical lines superim
icaldevice for determining the necessary controlling
parameters, and means for controlling the application of
energy from the source to the battery.
In the particular example of a normal, discharged
nickel-cadmium battery, a useful charging pattern in
posed on the curve. While the curve is subject to varia
tions in speci?c values of voltage or of time, the general
form is similar for all nickel-cadmium batteries includ
ing one or more cells, and the following discussion
accord with this invention is to apply a fast-rate con
stant charge current to the battery until two consecu
tive inflection points are passed, speci?cally, a ?rst one
applies equally to all such batteries.
Region I of FIG. 1 represents the initial stage of
voltage change which occurs when the charging cycle
is ?rst started. In this Region, the voltage is subject to
at which the sign of the slope of dV/dt (that is, the sign
of dZV/dtZ) changes from negative to positive followed
signi?cant variations based on the initial charge level of
by a second one at which the sign changes from positive
the battery, its history of charge or discharge, etc. Since
the shape of this Region can vary, it is indicated in FIG.
These analyses will be further clari?ed with reference 25 1 by a dotted line.
to negative. '
to the voltage variation of a normal nickel-cadmium
Because the information in Region I varies, it is usu
ally preferable to ignore this segment of the curve. The
battery in the detailed description hereinafter; for the
present, it is suf?cient to note that one basic concept
battery will generally traverse Region I completely
presented herein is that of inflection point analysis.
within the ?rst 30 to 60 seconds of charging and enter
Speci?c techniques of analysis and speci?c sequences 30 Region II; in general, the voltage in the Region I and
adapted to accommodate different battery couples may
period increases relatively rapidly from the initial shelf
voltage and the short peaks which may occur in this
readily be developed within the context of this general
Region are not harmful.
As the battery approaches a more stable charging
35 regime, it enters the portion of the curve designated
Region II. Region II may be of fairly long duration with
FIG. 1 is a graph illustrating the variation of voltage
little or no increase in voltage. During this time, most of
the internal chemical conversion of the charging pro
cess takes place. When signi?cant portions of the active
material have been converted, the battery begins to
as a function of time during the charge cycle of a nickel
cadmium battery;
FIG. 2 is a block diagram illustrating the primary
elements in a- battery charger in accordance with this
approach full charge and the voltage begins to increase
more rapidly. The inflection point A in the curve from
FIGS. 3 and 4 together comprise'a schematic dia
a decreasing rate of increase to an increasing rate of
gram illustrating speci?c circuits which may be pro
increase is identi?ed as the transition from Region II to
vided in accordance ‘with this invention to form the
45 Region III.
block diagram of FIG. 2;
Region III is characterized by a relatively rapid volt
FIGS. 5 through 9 schematically illustrate the se
age increase as more and more of the active material is
quence of operations performed by the microcomputer
converted to the charged state. As the battery ap
shown in FIG. 4;
full charge more closely, that is, when perhaps
FIGS. 10-13 are graphs illustrating the variation of 50 proaches
90 to 95% of its active material has been converted
voltage'as a function of time during the charge cycle of
chemically, oxygen begins to evolve. This produces an
several different batteries; and
increase in the internal pressure and also an increase in
FIG. 14 is a graph illustrating ,the variation of current
the temperature of the cell. Due to these effects, the
as a function of time during the charge cycle of a nickel
rapid increase in battery voltage begins to slow and
cadmium battery.
In the following speci?cation, an explanation is given
of the battery charging process of nickel-cadmium bat
55 another inflection point occurs in the curve. This sec
ond inflection point is identi?ed as the transition point
between Regions III and IV, point B.
Within Region IV, the ?nal portions of the active
teries. The inventive'method for either monitoring or
terminating the battery charging process is next de
scribed, including several alternative terminating modes
used for either protection or supplemental termination.
The apparatus of this invention is then presented, in
cluding a preferred, detailed schematic circuit and a
material are being converted to the chemical composi
tion of the fully charged battery. At the same time, due
to oxygen evolution from material already converted,
the internal pressure increase and the heating contribute
' to a slowing in the rate of voltage increase until the
preferred embodiment of the operational sequence per
voltage stabilizes at some peak value for a short period
formed by thev microcomputer. Finally,'av general de 65 of time. This is designated as the transition between
scription of the application‘ of this'vinvention‘ to other, Regions IV and V.
types of batteries and to,‘ other charging modes is pro‘ ‘
" Within Region V, if charging is continued, the 'volt
‘ ‘age of the cell starts to decrease due to additional heat=
ing as virtually all of the applied energy is converted '
exactly that order, and only then, the battery charging
into heat and the negative temperature coef?cient of the
battery voltage causes the voltage to decrease. Contin
current can be discontinued or reduced to a mainte
nance or topping mode if desired, with absolute assur
ance that the battery has been brought to a full state of
ued application of charging energy in this Region
would eventually cause damage to the battery, either
through venting or damage to the separator.
As previously noted, the relative time duration, slope
charge regardless of its temperature, history, or individ
ual cell characteristics. Because of the accuracy of this
determination, this method can even be applied to bat
teries which are constructed for use only with trickle
or value of any portion of this curve may be modi?ed
by such factors as the initial temperature of the battery,
the charge or discharge history of the battery, the par
ticular manufacturing characteristics and the individual
It should be noted that the exact sequence of occur
rence of these in?ection points is critical to this inven
tion. While the preferred method of this invention in
characteristics of the battery cell. However, the major
volves ignoring the voltage changes which occur
within the ?rst 30—60 seconds of the charging cycle, the
tery which is brought from a substantially discharged 5 changes which occur in Region I may overlap slightly
into the time period within which the data sampling
state to a fully charged state at a constant, relatively
high current.
apparatus of this invention is operative. In that event, an
inappropriate in?ection point may occur near the begin
In speci?c accordance with the present invention, the
ning of Region II. The apparatus of this invention is
above described curve and the information contained
therein are utilized in a novel manner to provide an 20 designed so that it will ignore such in?ection points
aspects of this curve and of each of its Regions will be
identi?able in any non-defective nickel-cadmium bat~
improved battery charging method. This method is
until those identi?ed above occur in the proper se
An alternative statement of this technique can be
much more accurate than those previously used and is,
in fact, so improved that it permits rapid charging of
any nickel-cadmium battery cell in a minimum time
considering reasonable system cost.
Up to the present time, rapid charging techniques for
made based on the identi?cation of changes of sign of
the second derivative of the voltage with respect to
batteries have carried the risk of serious damage to the
time. Speci?cally, Region II is characterized by the
gradual decrease of the slope or rate of charge of volt
battery. To help in avoiding this problem, ordinary
age versus time. For a fully discharged battery, Region
II constitutes the largest portion of the charging period
battery cells are usually manufactured for use in con
junction only with so-called “trickle chargers” which
30 with voltage over most of this period increasing at a
require some 16-24 hours to bring a battery from a
relatively low rate. As the battery approaches full
charge, the voltage again starts to increase somewhat
more rapidly. Thus, the slope which had been becoming
substantially discharged state to approximately its fully
charged state. Even when this time penalty is accepted,
progressively smaller and smaller starts to become
such chargers can be harmful to the battery cells over a
long period of use.
35 larger again. This can be described as an in?ection point
Rapid chargers are available for nickel-cadmium cells
which will bring a battery to approximately full charge
within approximately one hour. However, these char
gers require the use of high priced cells manufactured
by special techniques so that the cells are capable of 40
or a change in sign of the second derivative of voltage
with respect to time. Thus, we have a ?rst such change
in sign giving indication that the battery is nearing the
full charge state.
During Region III the slope of the voltage-time
withstanding the possible harmful effects of rapid
curve increases further and further as the battery comes
charging. This is due to the fact that the chargers cut off
closer to full charge. At or near the full charge point,
there is the transition between Regions III and IV at
by one or another of the methods described above with
their attendant inaccuracies.
which the slope of voltage stops increasing and starts
45 decreasing to smaller and smaller values as Region IV
progresses. Here again, a change in the sign of the sec
In accordance with this invention, a new method of
ond derivative of the voltage-time curve occurs. This
controlling the battery charge process is provided
decreasing slope in Region IV indicates that virtually
which identi?es exactly the conditions in the particular
all of the active material in the cell has been changed to
the charged state and that the energy going into the cell
is beginning to convert into heat rather than continuing
the charging process. Thus it is desirable to terminate
battery undergoing charge and correspondingly con
trols the application of charge current. Because of this
new technique, a high rate charge current can be ap
plied to the battery so that the battery is brought
through its initial stages in the minimum possible time,
charge during the early or middle part of Region IV of
the voltage time curve.
for example, as little as 15 minutes for a fully discharged
These two above described changes in sign of the
battery. As the battery approaches full charge, its con
dition is identi?ed accurately and the charging current
second derivative of the voltage-time curve are charac
is reduced or cut off at exactly the proper moment in the
cells during the charging process. They provide a
unique and reliable indication of the state of charge of
the battery. A particularly important aspect of the
charge cycle.
Application of this new technique requires very so 60
phisticated processing of the available information. In
concise form, as applied speci?cally to nickel-cadmium
batteries, the method of this invention involves the
identi?cation of the in?ection point between Regions II
and III and by the identi?cation of the subsequent or
following in?ection point between Regions III and IV.
Once these two in?ection points have been identi?ed
and it has been con?rmed that their occurrence is in
teristic of nickel-cadmium and other electrochemical
method of this invention is, accordingly, the use of one
or more of these observable changes of sign of the sec
ond derivative of the voltage-time curve to determine
when to terminate battery charging.
.The method of this invention of observing these in
?ection points, or of changes in the sign of the second
derivative of the voltage-time curve of the battery
charging process, can be implemented in serveral ways
and entering Region V. Within a fairly short time after
including the apparatus hereinafter described. For other
it has been placed on charge (e.g., 1-3 minutes) the‘
types of electrochemical cells or different types of
charging systems,‘ other sequences of in?ection points
may be required, but the detection of all of these types
of second derivative sign changes and speci?c sequen
ces of them are intended to be included within the scope
_ of this‘ general method.
One principal advantage of in?ection point analysis is
that it does not depend on the actual value of the volt
age of the cell nor does it depend upon the value of the O
rate of change, or slope, or voltage. It is an analysis of
battery will enter Region V and its voltage will begin to
decrease. As soon as the negative voltage change is.
large enough to indicate to the apparatus that the func—
tion of voltage with respect to time is no longer mono
tonic, the apparatus will discontinue the fast charge
rate. Preferably, the charging mode then shifts into a
maintenance mode as will be hereinafter described.
Since the high rate is only maintained for a short period
of time, the battery will not be damaged by this se
quence. It is also noted that even defective batteries will
not be driven into a hazardous condition by the continu
ation of a maintenance charge mode after shut down of
those points where the rate of change of voltage (that is,
the slope of voltage) changes from decreasing to in
creasing or from increasing to decreasing. In turn, these
points are directly relates to the actual chemical occur
rences withinthe battery being charged.
the high rate due to a negative voltage change.
' Thus, determination of state of charge and hence the I
most appropriate time to terminate charge is dependent
only upon very universal characteristics of such batter
While the chargepro?le of nickel-cadmium batteries
vdoes not lend itself to advantageous use of this tech
ies and not on the particular cell characteristics or char 20 nique, other battery couples exhibit pro?les wherein
termination should be predicated upon the occurrence
acteristics which might be due to the history of use such
as storage or very heavy use. It is thus more reliable and . of a particular voltage slope. Thus, in a couple wherein
Region V involves a slow downward drift of voltage
i a more valid indication of the most appropriate time at
which to terminate charge than previous methods.
' I rather than a sharp decrease as in the nickel-cadmium
. r In some cases, the in?ection point technique which is 25
pro?le, the occurrence of a negative slope is useful in
appropriate for normal conditions may not be adequate, .
for example, if a battery is damaged or defective or if a
just described.
user inadvertently places a fully charged ‘battery on
charge. In these cases, the normal indicative points may
not occur at all or they may possibly occur within the
?rst period of time in which the apparatus is not sam
pling data. In order to protect against these possibilities,
the present invention further includes the provision of
the same manner as the absolute voltage change analysis .
Insome. cases of dried or otherwise damaged nickel
.cadmium cells, application of a charging current can
cause the voltage to increase to a level signi?cantly
beyond the normal voltage of an operative cell. Ac
speci?c controlling techniques or modes which may be
cordingly, the apparatus of this invention includes the
nates charge if a predetermined level of voltage is en
countered. In other battery couples, this may serve as a
primary charge termination mode rather than as a sec
used in combination with the basic method described 35 provision of a voltage level sensing means which termi
A ?rst of these techniques which can be incorporated
is that of terminating the application of charging cur
rent to the battery immediately upon the occurrence of
a negative change of voltage. By reviewing the curve of
FIG. 1 it will be noted that there is not point in the
normal charge cycle when a negative voltage change‘
ondary safeguard.
In other defective cells, the application of a high
charge current may simply be allowed to continue for
an undue length of time because the energy is being
occurs. Thus, if a negative voltage change is encoun 45 converted to heat or to oxygen evolution, etc. In these
instances, the defect in the cell may prevent the in?ec
tered, it must mean that the battery is either defective or
tion points from occurring and a maximum time cutoff
that it is already fully charged and that it has entered
Region V of the curve. Accordingly, provision is pref
erably included to terminate the high rate charge imme
diately upon the occurrence of a negative voltage 50
change. Preferably, the value of this change should be
large enough so that termination is not inadvertently
caused by inaccuracies in the monitoring equipment.
It is also noted that the absolute voltage change anal
ysis is utilized to prevent fast charging of a fully
charged battery which is inadvertently placed on fast
charge by the operator. Speci?cally, a fully charged
battery to which a high current is applied will traverse
most, if not all of Regions 1, II and III very quickly. In
many cases, this will occur in the time period which a
normally discharged battery would require to traverse '
Region I. Since the system is instructed not to look for
' in?ection points during the ?rst 30 to 60 second portion
of the cycle, at least one and perhaps both of the signi?
cant in?ection points, points A and B will pass before
the system begins to monitor for them.
Therefore, as monitoring of the fully charged battery‘
begins, the battery will be passing through Region IV
is provided.
In each of the above cases, the exact quantity chosen
for the negative voltage change, for the negative
change in voltage slope, for the absolute level of volt
age reached, or for the maximum time reached is, of
course, a predetermined number based on the type of
cell for which the particular charger is intended.
After the main charge regime is terminated by one or
more of the above ?ve methods of analysis, it is pre
ferred to proceed into two other charge regimes. The
?rst of these is a programed overcharge or surcharge to
insure that all possible active material in the cell is fully
converted to the charged state and that all possible
capacity in the cell will be available to the user. The
preferred method of overcharge or surcharge is to
charge at a relatively low charge rate for a ?xed amount
of time depending on the type and size of the cell. This
guarantees that the cell is given a full amount of addi
tional charge but at a low enough rate to avoid damage.
The ?xed time also means that the cell is not subject to
long periods of time of overcharge which would subject
the cell to increased internal pressures and heat which
would eventually damage internal structures such as
the full charge current to be applied to the battery
through the ampli?er 12 for a predetermined period of
time, usually between 30 and 60 seconds, which allows
the battery to be brought through the segment of FIG.
1 identi?ed as Region I. For nickel-cadmium batteries
of the sub-C size, the preferred time is 40 seconds. This
At the end of the surcharge or overcharge period it is
very desirable to provide only a maintenance charge
application of power can be at full rated current since
which is used to compensate for the internal self-dis
even a defective battery or a fully charged battery will
charge characteristics of all electrochemical cells in
not be seriously damaged by the application of this
cluding nickel-cadmium cells. Nickel-cadmium cells 0 power for this short an interval. The application of
can self-discharge as much as 10% to 30% per month
power is controlled by the micro computer 18 by its
depending on the storage temperature and the particu
selection of the appropriate current control resistor 20
lar characteristics of the cell. One method of mainte
through which to apply the input signal to the current
nance charging is to apply a low to medium charge
ampli?er 12. After an appropriate period of time has
current for a short period of time one or more times per 15 passed as described above, the microcomputer 18 makes
day. The preferred rate is a charging rate of “C” (a
use of the analog-to-digital converter (A/D) 22 to de
charge rate representing the same number of amperes of
termine the battery voltage. The converter 22 is prefer
charge as the ampere-hour rated capacity of the cell) for
ably of the successive approximation type in which
15 to 30 seconds every 6 hours. This provides approxi
successive approximate digital values of battery voltage
mately twice the typical loss rate in ampere hours of the
generated by the microcomputer 18 are compared to
cell without causing any signi?cant heating or pressure
the actual battery voltage until a close approximation is
buildup in the cell. The particular charge rate and par
achieved. This information is then fed bck into the mi
ticular choice of charged time to resting time can be
crocomputer 18 which then proceeds to execute its
varied over a very wide range. The method is merely to
program so as to charge the battery in accordance with
replace the calculated or measured energy lost to self 25 the method described above.
discharge of the cell.
In addition to the basic elements of the block diagram
already mentioned, the circuit should provide certain
. FIG. 2 is a block diagram showing the major ele
additional features. If the battery charger is of a type
adapted to handle a variety of battery sizes and types, a
battery ‘type selection circuit 24 is included which se
ments of electronic circuitry which are used in accor
dance with this invention to implement the above de
lects the speci?c program for the given battery type
scribed charging method. The ?ow of charging current
from several stored in the computer. This may be done
either by the operator or automatically by some identi?
cation means such as particular terminal types provided
on the battery itself.
The system also preferably includes a temperature
cutoff circuit 26. The purpose of this circuit is to pre
vent charging if the ambient temperature is either so
in FIG. 2 runs from an AC power input plug 8, connect
able to an ordinary source of line current, to a power
supply 10 which converts the AC input to low voltage
DC. Next, the current passes through a resistor-con
trolled current ampli?er 12, and then through a char
ge/test switch 14 and ?nally to the output terminals 15 j
at which a single or multi cell battery to be charged is
low or so high as to cause damage to the battery or to
connected. The power supply may, of course, be any 40 the charging circuit itself.
alternative source of DC power such as a larger battery
Reset circuit 28 is provided to reset the entire mi
or a converter operated from a DC source. The ampli
crocomputer program to time zero as soon as power is
?er is preferably a standard series-pass current regulator
supplied to the system, or in the event of a power inter
although other types of controllable current ampli?ers
could be used. The charge/test switch normally con
nects the current ampli?er 12 to the battery for the
application of charging current; this switch also in
ruption. This is done to prevent unpredictable charging
45 effects which might occur if the computer were to be
initiated at an incorrect point in its program.
Finally, the operator display circuit 30 provides for
cludes a test position for use in a test mode which is
communicating such information as may be appropriate
described below.
The remainder of the block diagram illustrates a pre
to the operator. In the case of a simple charger for use
by a consumer, the display 30 may consist only of an
ferred embodiment of the apparatus for performing the
method of this invention. In the illustrated embodiment,
illumination lamp to indicate that charging is in process.
a start switch 16 is provided; this comprises a momen
quali?ed technician, the display circuit may provide for
tary contact switch for initiating the sequence of opera
tions. It is connected to one input port of a microcom
the display of a variety of different information which
may be of use to the technician in evaluating the condi
puter 18. In the preferred embodiment of this invention,
tion of the battery.
this is an Intel type 8048 microcomputer. This is a self
contained computer including a program memory for
storing instructions, a register memory and a central
gram of one suitable embodiment of FIG. 2. The respec
tive segments of the circuit as identi?ed in FIG. 2 are
In the case of a complex battery charger used by a
FIGS. 3 and 4‘ together comprise a schematic dia
processing unit (CPU) for controlling the execution of
enclosed in dotted line boxes identi?ed by correspond
the stored instructions. The 8048 microcomputer is
more completely described in the publication entitled
ing numbers.
In the speci?c embodiment of these ?gures, a conven
tional line-plug 8 is provided for connection to a source
lished by the Intel Corporation of Santa Clara, Calif.
of power. The power supply 10 includes a transformer
65 T1 and a full wave bridge recti?er made up of diodes
When the start switch 16 is actuated, which could be
D1—D4. The output from the bridge, which may be
“Microcomputer User’s Manual” No. 98-270A, pub
accomplished automatically on connection of a battery
to the output lines, the microcomputer 18 ?rst allows
approximately 20 volts DC, is applied through ampli
?er 12 and switch 14 to the battery (shown in dotted
applied to a ?lter made up of resistor R1, diode D5 and
ladder R43-R50 as selected by the computer. Resistors
R44-R50 each have values which are twice the value of
capacitor C1 and to voltage regulator 1C1. Regulated
the preceding sequential resistor. The computer, under
voltages of 25 volts and 5 volts for use in the other
portions of the Circuit are taken at the indicated output
inafter, selects‘ an ‘initial minimum value, for example, by
line illustration). A portion of the bridge output is also
the instruction of its program as will be described here
turning on only R43“ This develops a voltage across
ICZC which is compared in IC3¢ to the signal received
from the battery. If this minimum voltage supplied from
the computer is not equal to or greater than the battery
voltage, then successively increased values are tried by
The resistor-controlled current'ampli?e'r 12 operates
according to outputs taken from the microcomputer 18
through current control resistors 20 shown in FIG. 4. In
accordance with its internal program, the computer 18
selects a current level by completing‘ a circuit through
This controls the input to operational ampli?er ICzb
the computer until a match is reached. This information
is communicated back to the computer from the output
of IC3¢ and the computer uses the last input to the com
which is taken at the midpoint of a voltage divider made
up of the parallel combination of resistors R13 and R17,
and the selected current control resistor. The output
parison circuit as the battery voltage.
In reset circuit 28, the comparator IC3d ampli?es a
signal derived from the 25 volt supply and compares it
one of the current control resistors R29, R30, or R31.
from the ampli?er ICZI, is compared to the voltage de
to a 5 volt reference. If the 25 volt signal goes below
veloped across a current shunt resistor R5. Any error
approximately 10 volts, as would occur upon the re
signal due to a difference is ampli?ed by operational
ampli?er IC;,, and applied to driver transistor Q3. The
output of transistor Q3 is applied to current control
transistors Q1 and Q; to produce a very stable constant
current which is applied- to the battery through 81¢.
moval of power from the system either due to a power
failure or due to the operator unplugging the charger,
the output signal from the comparator instructs the
computer to return all of its programming functions to
the initial conditions; that is, those which must be used
when a new charge cycle is initiated. This can occur
If the output current to the battery cannot reach the
selected current level, for example because there is no
battery connected, transistor Q3 vis turned fully on
either during power-down as the power is falling from
normal input to zero due to a power failure or during
power-up as the power is building from zero ‘to its nor
mal level when the system is ?rst connected to a power
source. In‘ either case, this system is useful to ensure that
the computer does not begin a cycle at some indetermi
which, through the comparison ampli?er IC3,,, supplies
a signal to the computer which turns- the system off.
As shown in’FIG. 3, a momentary contact push but
ton switch 16, which may be operator-controlled or
may be built into the battery socket supplies a signal to
the battery to indicate that the charging cycle should be
initiated. This could also be accomplished by monitor
ing for the presence of battery voltage or current ?ow.
Selection'circuit 24 (FIG. 3) comprises a plurality of
selector switches S3, S4 which allow the operator to
select a particular computer ‘program appropriate to a
particular battery. Diodes D7-D10 are provided tov pro
nate midpoint in its cycle with inappropriate informa
tion stored in its memory.
unique terminals to which different battery types are
connected. Also, the entire selection circuit 24 might be
omitted if the charger is intended for use with only a
single battery type. I
rangement shown, the voltage at the'midpoint of the
voltage divider comprising resistor R35 and thermistor
TH1 controls the input to both sides of the comparator
ampli?er IC31,. In the case of a high‘temperature (e.g.,
125° F.), the resistance of TI-I1 is low which reduces the
voltage input to the positive side of IC3’1,;vin the case of
a low temperature (e.g., 25° F.), the resistance of TH; is
high which increases the voltage at the negative side of
1C3], Either extreme produces a low output signal‘ from
IC3b which instructs the computer to discontinue charg
ternatively, the display might comprise simply a single
indicator lamp.
Finally, element 14 (FIG. 3) comprises a charge/test
switch. In the normal, charge position S11, and S16 con
Temperature cut-off circuit 26 comprises a safety
circuit to prevent operation at temperatures outside a
predetermined permissible range. In the particular ar
As illustrated, the display preferably comprises two
seven segment display elements and transistors Q4 and
Q5 which form a conventional strobing control which
enables eight output lines to control both displays. Al
tect the computer 18. Alternatively, this selection could
be provided automatically by using different sets of
The display system 30 is utilized by the computer to
communicate appropriate information to an operator.
In subcircuit 22, thev battery develops an‘ input signal
across the voltage divider R4/R67 which is ampli?ed in
nect the current controlled ampli?er 12 and resistor
network (items 12 and 20 of FIG. 2) so that current
from power supply 10 is supplied through S“, to transis
tors Q1 and Q; to switch Slc to the battery with a return
path through resistor R5. In the test position, the battery
is connected through S11, to transistors Q1 and Q2
through switch'Sk to resistor R2 and returning through
resistor R5 to the battery. For example, this could allow
the system to be used to discharge the battery at a pre
_ determined rate and, by means of appropriate program
ming, to determine and display the ampere-hour capac
ity of the battery. In addition, switch 51,, provides an
alternate signal to the microcomputer ‘18 to instruct it to
enter the charge program or a separate discharge pro‘
gram wherein it tests the condition of the battery.
In one embodiment of FIGS. 3 and 4, the following
circuit elements were used:
operational amplifier ICZd. The resistances'R64, R65 and
R66 and capacitors C9 and C10 comprise a ?lter on the
\ output of ICgd and ‘this signal 'is used as one input to
comparator ampli?er IC3C.
10 ohm 5 watt
.3 ohm 1 watt '
' R3
lk ohm 5 watt
8.2k ohm } watt
10k ohm 1 watt
Trimpot 100k ohm
100k ohm
developed through operational ‘ampli?er ICZCv from a
voltage divider comprising 'the parallel resistors R52 and
.1 ohm l watt
10 ohm } watt
' 12 ohm i watt
7 R21
l_0k ohm } watt
220k ohm l watt
R53 and a binary’ coded combination of the‘ resistor
‘ ' R23
lOk ohm 1 watt
At the same time, another input to comparator 1C3‘. is 65
560'ohm i watt
R19 ,
100k ohm 2 watt
.2_2k_ohm l watt
560 ohm 5 watt
10k ohm 3 watt
10k ohm l watt
' R25
lOk ohm 3 watt
Trimpot 100k ohm
lk ohm 3 watt
10k ohm .1, watt
2.2k ohm 3 watt
I Megohm 3 watt
10k ohm 3 watt
Trimpot 3k ohm
8.2k ohm } watt
100k ohm 3 watt
l2k ohm 5 watt
sets all operations of the computer 18 to an initial or
“reset” mode. In the flow chart, the “start” block 110
signi?es the application of the start signal to the com
puter due to the closing of the start switch 16 of FIG. 2.
Immediately, the internal total time register is set at 0.
This is indicated by block 112. The further steps of the
process shown in FIGS. 5-8 are then performed by the
4.7k ohm % watt
10k ohm 5 watt
10k ohm } watt
1 Megohm 3 watt
33k ohm 3 watt
22k ohm 5 watt
1 Megohm 2 watt
10k ohm 3 watt
47k ohm 5 watt
33k ohm l watt
The next step in the process, identi?ed as block 114,
is to increment the total time register. Then the program
moves to block 116 which does a comparison between
4.7k ohm & watt
22k ohm 3 watt
22k ohm 3 watt
100k ohm 2 watt
33k ohm 5 watt
680 ohm 3 watt
lk ohm 3 watt
lk ohm 3 watt
l.8k ohm 1 watt
, C1
5k ohm 1 watt
l0k ohm 3 watt
20k ohm l watt
.l microfarads 35 volts
l0 microfarads 35 volts
l microl'arads 35 volts
.1 microfarads 35 volts
20 or to a surcharge mode or to a maintenance mode if
10 microfarads 35 volts
80k ohm A watt
160k ohm 2 watt
10 microfarads 35 volts
3 amp 50 volts
- 320k ohm } watt
3 amp 50 volts
640k ohm l watt
270 ohm 3 watt
3 amp 50 volts
3 amp 50 volts
Trimpot 3k ohm
1 amp 50 volts
10k ohm } watt
Zener diode
’ 5.6 volts 5 watt
100k ohm } watt
Type IN4l48
Type IN4148
Type IN4148
may also involve changing to a timed overcharge mode
If the total time has not been reached, which it will
not this ?rst time through, the microcomputer goes on
to block 120. Here, the time register is again used to
determine whether this is the ?rst time through this
sequence of steps. If it is, then the program moves to the
series of steps 122-128 which direct the computer to set
up certain registers within the computer so that they are
30 rady for use later in the program. First, as indicated at
block 122, a flag identi?ed as F¢ is cleared. This ?ag
.l amp 50 volts
220k ohm} watt
"t _,
R50 " iflOk'ohm } watt
.1 amp 50 volts
. _
10k ohm } watt
Type IN4l48
10k ohm 1 watt ,
- -.1 amp 50 volts
2.2k ohm } watt
stop the charging cycle, including either turning off the
charging current or turning it to a lower value. This
40k ohm 3 watt
cates the execution of the sequence of instructions to
10 microfarads 35 volts
.1 microfarads 35 volts
15 reached, the sequence moves to block 118 which indi
20 picafarads 35 volts
a maximum allowable time as set for the particular bat
tery and the time that has elapsed. If the comparison
shows that the maximum allowable total time has been
1000 microfarads 35 volts
I Djl
will later be set upon the occurrence of a ?rst in?ection
point or change in sign of the second derivative. The
-.1 amp 50 volts
Type IN4148
program then continues through block 124, 126 and 128.
.1 amp 50 volts
Type IN4148
As indicated in the drawing, each of these steps controls
the placement of an initial value in particular registers,
namely, “Minimum Slope”, “Maximum Slope”, and
“Maximum Voltage Sum” respectively. The “Minimum
.lram'p 50 volts
PNP transistor 3 amp 40'vo1t type TIP-30
Q2 7 ' __NPN transistor 15 amp 40 volt type TIP-35
‘ NPN transistor .5 amp 40 volt type MPS A05
' NPNtransistor .5 amp 40 volt type MPS A05
NPN transistor .5 amp 40 volt type MPS A05
Voltage regulator 5 volt .5 amp type 78M05
Quad operational ampli?er type LM 324
Quad comparator type MC 3302
Microcomputer type 8048
Transformer 120/240 volt AC input
7 segment light-emitting diode display common cathode
7 segment light-emitting diode display common cathode
Slow blow fuse, l amp
Fuse, 5 amps
Thermistor RLZSFl
Switch 3 pole double throw (3 amp contacts)
Switch SPST N.0. momentary
Switch SPST
Switch SPST
Switch SPST
l0-20 volt AC output l-5 amps
Slope” register is set to a large number, while the “Max
imum Slope” and “Maximum Voltage Sum” registers
are each set to a large negative number such as
—10,000.\The use of these registers will be described
below. Thereafter, the program moves to block 130
‘designated “loop 2”. This is a common return location
45 to which the program is redirected after each of several
alternative sequences have been completed. In this in
stance, after the three registers have been initialized as
described above, the program moves through block 130
to block 132.
In block 132, the stated interrogation is “has two
seconds gone by!”. Block 132 together with the closed
loop 133 for a negative response to this interrogation
simply amount to a delay circuit to prevent the program
from proceeding until a period of time, arbitrarily se
lected to be two seconds, has passed since the last time
that the time register was incremented in accordance
with block 114. After each such increment, a two sec
ond timer is restarted and it runs while the computer
FIGS. 5-8 comprise a flow chart of the basic opera
program proceeds through its next sequence of steps. At
tions which are performed within the microcomputer.
The ?ow chart illustrated in FIGS. 5-8 summarizes the 60 the end of the sequence, the program returns to block
130 and the computer is held in the delay loop until two
program steps and has been prepared at a level of detail
seconds have passed. The time register is then incre
which would permit an experienced programmer to
complete the detaled implementation of this invention
mentally increased and the computer proceeds to its
next sequence of steps.
in a type 8048 microcomputer but which, at the same
time, is not so detailed as to require repetitious descrip 65 . The program then continues through the previously
tion of iterative steps.
As has previously been noted, when power is ?rst
applied to the system, the reset circuit 26 automatically
described loop. The interrogation of block 116 is asked
and answered in the same manner as previously de
scribed and, since the maximum allowable time has not
yet been reached, the program moves directly to block
120. When the interrogation of block 120 is asked, the
answer will be in the negative since this is the second
then it is known that the battery is somewhere in Re
gions I-IV and charging can safely continue.
It should be noted that the value K2 is a small number.
time through this sequence. At this point, the program
directs the computer through location 1 in FIG. 5 to
location 1 in FIG. 6 and thus into block 134.
This instruction, namely, to read the voltage and put
in “Tempsum”, operates the analog-to-digital converter
Its purpose is to prevent spurious or transient errors
caused by drift in the electronic circuit values, or small
negative changes in the battery voltage, etc., from shut
ting down the charging sequence. It is also noted that
this test is preferably performed even during the initial
period identi?ed as Region I of FIG. 1 wherein the
as previously described in connection with FIG. 2 and
stores the resultant digital statement of the battery volt 0 battery voltage is varying in a somewhat undetermined
manner. This is because a negative change in battery
age in a storage register in the microprocessor. This
voltage which exceeds K2 even in this Region is also
register is referred to as “Tempsum”.
indicative of a defective battery. K; may equal 25 milli
The program sequence next proceeds to block 136
volts per cell for nickel-cadmium batteries.
where the descriptive step is stated as “Calculate Dif
This is followed immediately by block 138 which
inquires whether the difference is negative. If the differ
The next stage in the process, identi?ed as block 146,
interrogates the timing system to determine whether a
slope calculation should be done. This actually repre
sents the beginning of the inflection point analysis previ
ously described; as will be clear from the following
description of FIGS. 5 and 6, the phrase “Slope Calcu
ence is either 0 or greater than 0, the answer is no and
the computer is directed by step 139 to stop charging.
This represents a sequence of steps which would be the
lation” used in this program identi?es the series of steps
which locate the in?ection points in the curve of FIG.
same as that stated above with regard to block 118. If
the difference is negative, then the answer is yes and the
program proceeds to block 140.
As indicated in step 146, the slope calculation is per
In fact, the combination of steps 134, 136, and 138 is 25 formed every minute beginning at an arbitrary time
a test for an excessively high level of battery voltage.
identified as K3 seconds. K3 is the time interval chosen
Thus, K1 is preset at a value which, for the particular
to allow the battery to pass through the initial stage
battery being charged, represents an excessively high
identi?ed previously as Region I and is usually between
30 and 60 seconds. K3 is preferably 40 seconds in the
level of voltage, which could only be reached by a
defective battery. Accordingly, if the value of voltage
case of nickel-cadmium batteries.
in the register “Tempsum” equals or exceeds K1, the
battery must necessarily be defective, or some portion
of the charger is defective, and the charging sequence
The ?rst several times through the program, the in
terrogation of step 146 will be answered in the negative
and, as indicated, the program returns to step 130. Thus,
until the total time registers equal the value K3, the
must be stopped immediately. For example, K1 may
equal 2 volts per cell for a nickel-cadmium battery. In
program simply directs the computer to monitor the
time and voltage to make sure that neither assigned
normal charging, the battery voltage will never equal
K1, and the answer to the interrogation of step 138 will
be af?rmative so that the program proceeds normally to
step 140.
In step 138, the register “Max. Voltage Sum” was set
to an initial large negative number. In step 140, the
value in “Tempsum” and the value in “Max. Voltage
Sum” are compared. If the value in “Tempsum” is
greater than that in “Max. Voltage Sum”, then the value
maximum has been exceeded, these checks being per
formed at steps 116 and 134-138 respectively, and also
monitors the voltage for a negative drop in steps
140-144. Once the total time register reaches K3, the
interrogation of step 146 is answered in the af?rmative
and the program passes through connection point 2 and
enters the series of steps shown in FIG. 7.
In FIG. 7, the program continues with step 148
in “Tempsum” is placed in the “Max. Voltage Sum” 45 which refers two additional register locations in the
register by instruction 142 and the program proceeds to
microcomputer. One is called “Sum” and the other is
step 144. If not, then the “Max. Voltage Sum” register
“Oldsum”. In step 148, the contents of the register
value is left unchanged and the program proceeds di
“Sum” are moved into the register location “Oldsum”
rectly to step 144.
and the previous contents of the register “Oldsum” are
In step 144, the difference between the values used in
cancelled. In Block 150, the contents of the latest read
“Tempsum” and in “Max. Voltage Sum” are compared
ings in “Tempsum” are transferred into the register
to another constant, K2, which is preset according to
location “Sum”. The sequence then moves to block 152
the battery being charged. In fact, the test being per
where a test is made to see if the time is equal to K3
formed by the series of program steps 140, 142 and 144
seconds. If it is, the program returns through Loop 2,
is that of checking to see if the voltage has moved 55 step 130. Thus, the ?rst entry into the steps of FIG. 7 at
downwardly by more than a given minimum amount
T=K3 simply sets a voltage reading in the “Sum” regis
from a previously achieved maximum value. As de
scribed above in the section entitled Absolute Voltage
Change Analysis, if this has occurred, this must indicate
that the battery has already passed its maximum charge
level and is in the region indicated as Region V in FIG.
1, or that the battery is defective. Accordingly, the
program is instructed to move to block 145 which stops
ter which will later be transferred into “Oldsum”. Cal
culation of a vslope requires at least two points on the
line and therefore the ?rst calculation can only be done
when the time equals 1 minute plus K3 when the previ
ous voltage value is present for comparison to the new
value. Of course, this is really an approximation of the
slope rather than an accurate determination.
Accordingly, if the time elapsed equals K3 seconds.
the charging process in the same manner as steps 118
65 the sequence goes back to loop 2, block 130 and contin
and 139.
ues for another minute. Subsequently, when the time
If this is not the case; that is, if the latest value of _
battery voltage present in “Tempsurn” is either equal to
equals K3 plus any integral number of minutes, the se
or greater than the largest value previously recorded,
quence goes on to block 154 where the difference in
value between the “Sum” register and the “Oldsum”
register is calculated and put into a register location
called “Slope”. The sequence then continues to block
In step 156, the register “Min. Slope” which was set
to an initial large value in step 124 is used. Speci?cally,
the value in “Slope” is subtracted from the value in
“Min. Slope” and the result tested to see if it is greater
than or equal to 0. If the “Slope” register is less than the
“FURTHR” into FIG. 9. There, the sequence contin
ues to block 170 where the slope value is tested to see if
it is less than the value in register “Max. Slope" by an
increment K5 which may be approximately the same in
value as K4. This is the test for the Region III-to-Region
IV transition shown in FIG. 1. If the slope is less than
“Max. Slope” by K5, then the charge cycle has reached
this second in?ection point and the charge cycle is
complete. The sequence then goes to block 172 and, the
previous .“Minimum Slope” register, which had been
charging process is terminated in the same manner as
initialized to a very large number, the “Slope” value is
put into the “Minimum Slope" register. Thus, once per
minute, each time through this program sequence, a
described in regard to step 118. If, however, the latest
slope is not less than the “Max. Slope” by a suf?cient
slope is calculated and a-check is done to see if the new
value of slope is less than the previous lowest slope
reading. If it is, this new slope is put into the “Minimum
Slope” register in block 158 and the sequence continues
increment, then the sequence returns to block 130 and
continues until one of the four charge method analyses
described above causes the charging sequence to stop.
In this way, this ?ow of operations takes the appara
tus through the methods of analysis described above,
testing at appropriate time intervals for time analysis of
excessive total time elapsed, for excessively high volt
Here, the slope reading just taken is subtracted from 20 age on the cell or battery, indicating possible damage,
the “Max. Slope” register which was initialized at block
for a drop in voltage from one period to another of
126 to a very small number. If this difference is less than
suf?cient magnitude indicating that the cell or battery is
0, meaning that the new value in the “Slope” register is
in Region V or for the sequence of second derivative
greater than the previous value in the “Max. Slope”
tests indicating that the cell or battery has gone through
register, then this slope value is put into the “Max. 25 the transition from Regions III to IV, as described in
Slope” register and replaces the old contents. This is
FIG. 1 in the change of sign of second derivative test.
to block 160. If the newest slope is not less than the
minimum slope, the sequence also goes to block 160.
done in block 162.
Next, the sequence ?ows to block 164 where a test is
done to see if the ?ag F E, which was cleared in step 122,
is set. Up to this time, it has not, so the sequence will
proceed through connection point 3 to block 166. At
The present invention, as thus far described, has been
directed to the pro?le of voltage change with time
block 166, a test is done to see if the latest slope value is
used is of the type generally known as a “constant cur
which occurs in a battery when the charging system
greater than the minimum slope by a preselected incre
rent” charger. This type of voltage change is actually
ment, K4. The value of K4 is selected to de?ne some
obtainable in several different ways. First, it may be
minimum value of positive change which must occur, to 35 obtained by applying a steady unchanging charging
avoid transient effects, before the system is allowed to
current to the battery and measuring the change of
recognize that the slope has stopped decreasing and is
voltage with time. In this method, the charger power
now increasing. In the case of nickel-cadmium batteries,
supply and current ampli?er may be chosen to provide
K4 may-be l5 millivolts per minute per cell. Once this
a predetermined current level at any battery voltage
occurs, an in?ection point will have been identi?ed by
between zero and a value slightly in excess of the volt
age of the battery at full charge. The current level is
If the slope value has not increased over the “Mini
chosen on‘ the basis of factors such as the charge effi
mum Slope” value by this necessary increment, the
ciency, the cost of the power supply and ampli?er, and
sequence returns to block 130 which is the loop 2 re
the desired time to fully charge a totally discharged
turn. This means that the slope is either continuing to 45 battery. In general, in nickel-cadmium batteries of the C
become less or if it is increasing, it has not increased
size or sub-C size, the current applied is about three
sufficiently. If the latest slope is greater than “Min.
times the C-rate of the battery. The C-rate of a battery
Slope" by K4, meaning that in?ection point has been
is a current in amperes which is numerically equal to its
passed (or that the sign of the second derivative has
ampere-hour capacity. A “3C” current would bring a
changed), the sequence ?ows to block 168 where ?ag 50 battery to full charge in about 20 minutes.
F¢ is complemented or set. This means, referring to
In other cases, charging rates such as C or 5C may be
FIG. 1, that the transition into Region III has been
selected; these would fully charge a discharged battery
made and that the charge cycle is well along toward
in about one hour or in about 12 minutes, respectively.
completion. From block 168 the sequence also contin
A second method of obtaining the voltage pro?le of
ues back to block 130 to continue the process as previ 55 FIG. 1 is by applying the charging current in pulses and
ously described.
measuring the rest voltage of the battery when the cur
At this point, although it is not shown in the ?ow
rent is zero. This is known as trough voltage sensing. In
chart, it is usually preferable to replace the value in the
a sense, the voltage measurements are taken at a “con
“Max. Slope” register with the value in the “Slope”
stant” current level of zero amps. The pro?le of voltage
register. This insures that additional slope values after
with time will correspond in form, although not in
the ?rst in?ection point will be compared to the actual
scale, to that shown in FIG. 1 and exactly the same
slope at the ?rst in?ection point and not to an earlier
value which may have been carried because it was
method of analysis as described above may be applied.
A third method of obtaining this same pro?le is to
slightly larger than the in?ection point value.
apply a current which may vary cyclically but which
Eventually, the process will continue through suf? 65 has a constant average value. If the measured voltage is
cient cycles so that it will arrive again at step 164. Now,
averaged over a similar time period, thus compensating
the response to this interrogation will be “yes” and the
for the cyclic variations in current, the voltage pro?le
program will proceed through the connection point
obtained is exactly the same in form as that shown in
FIG. 1, and again, the same method of analysis-may be
fast charge mode. The surcharge rate selected is gener
ally about one-half of the full charge rate. The ?xed
‘A fourth method of obtaining the same pro?le is to
period of time is calculated by determining how long it
allow the current to vary but to measure the voltage
only at the time when the current equals some prese
takes to add 25% of the full battery capacity to the
battery at the surcharge rate. At the end of that time,
lected constant level; again, this produces the same
the battery charger automatically terminates the full
results as the other methods just described.
charge mode and begins a maintenance mode cycle
In all of these instances, the voltage pro?le for a
which simply compensates for self-discharge.
given battery will assume the same general form. Since
FIG. 12 illustrates the charging curve for a lithium
the novel method of analysis described in this speci?ca 0 battery having an iron sul?de electrode. In this case, the
tion is a function only of the form of the pro?le and not
in?ection points occur much earlier in the charge cycle
of its actual value, this method may be applied to any of
and there are almost no distinguishing features of the
these charging techniques. For convenience, all of these
voltage pro?le after the second inflection point. Be
methods are commonly referred to by the term “voltage
cause of this voltage pro?le, it would be extremely
15 dif?cult to provide a reliable fast charger for such a
battery using only prior art techniques. In accordance
with the present invention, the in?ection points can be
determined very precisely. This-indicates that the bat
FIGS. 10-13 illustrate a variety of voltage pro?les for
tery is approximately at 45% of capacity. Accordingly,
particular examples of several different types of batter 20 a charging program for a lithium battery of this type
ies, all of which have been developed using the “con;
may use the same system for determining in?ection
stant current” method referred to above. Speci?cally,
points as has been described above, coupled with a
FIG. 10 is a representative pro?le obtained in the case
of a nickel-iron battery. It will be ‘noted that the general
timing sequence. When a battery is attached to the char
I appearance of this curve is similar to that of FIG. 1 and 25
in particular, similar inflection points occur at A’ and B’
as the battery approaches full charge. Thus, exactly the
same technique can be applied to the nickel-iron battery
as has been described for the nickel-cadmium. The only
differences are that the constants must be selected in
accordance with the needs of the particular battery,
considering its internal construction and the level of
current which it can accept, the number of cells and the
ger, a timer is started and it is set to discontinue the full
charge rate when enough time has passed to add ap
proximately 55% of the total battery capacity to the
battery. If no in?ection points are encountered during
this period, the timer alone shuts off the system at the
end of the period. This accommodates a battery which
may be placed on charge although it already has a rea
sonably full charge.
However, if the in?ection points are encountered
corresponding maximum voltage; and the maximum
before the time has expired, then the timer is simply
time or maximum voltage which can be accepted with
out damage. Also, the small scale of the changes in the \
charged, or only partially charged, initially will receive
voltage pro?le require the system of voltage measure
ment to have a higher resolution than is true in the case
of a nickel-cadmium battery. In principle, however, the
method of charging is substantially identical.
FIG.‘ 11 illustrates the charging curve of a representa
tive lead acid battery. Once again, it can be seen that the
?ve Regions as described in connection with FIG. 1 are
repeated in the case of the typical lead acid pro?le and
similar inflection points A" and B” occur. The only
differences are that the overall change of voltage is
larger and the rate of change in Region III is greater.
However, since the Regions are the same and the se
restarted. This ensures that a battery which was dis
its full charge.
FIG. 13 illustrates still another variation of voltage
pro?le, namely, that for a silver cadmium battery. In
this instance, simple determination of two consecutive
in?ection points is not suf?cient; addition of energy to a
battery which is fully discharged should produce four
consecutive in?ection points before full charge is
In order to fully charge this battery, another combi
nation of the in?ection point analysis method with the
alternative charge termination modes previously de
scribed'will fully charge this battery. Speci?cally, the
quence of in?ection points is the‘ same, essentially the
charger is arranged to seek the four consecutive in?ec
used for lead acid batteries.
discharged to fully charged; if this occurs, the charger
same method as described in connection with nickel 50 tion points which indicate that the battery being
cadmium batteries and nickel iron batteries can again be ‘charged has gone through its entire cycle from fully
However, it has been found that full (100%) charging
of a lead acid battery can be better obtained by the
additional application of a surcharge after the second
in?ection point has been reached. This is due to the
internal chemistry of the lead acid battery which causes
the ?nal addition of energy to occur at a slower rate
than in the case of a nickel-cadmium battery. Therefore,
the optimum charge method for lead acid batteries is to
apply the in?ection point method of analysis as previ
ously described, and, when the second in?ection point
terminates the application of the fast rate charge cur
rent. However, this termination mode alone is not suf?
cient. In addition, the system is instructed to compare
the total voltage to some preselected value after each
in?ection point is‘measured. If the voltage is above the
preselected level when an in?ection point is reached, it
will then be known that the battery was not fully dis
60 . charged when the charge program was started and that
the battery is now fully charged. Accordingly, the ap
plication of the full rate current is discontinued. Thus,
the system accommodates both batteries which are
between Regions III and IV is identi?ed, the microcom
placed on charge while already either fully or partially
puter is instructed to shift the charging rate to an inter
mediate level. This intermediate rate is then applied for 65 charged and also batteries which are fully discharged;
in both cases, the charger brings the battery precisely to
a ?xed period of time.
its full charge capacity without the harmful effects of
In general, lead acid batteries have 'aistructure which‘
permit the constant current to be about'C or 2C'in the
prior art charging techniques.
Of course, in devising the method and system for
each of the batteries mentioned in connection with
FIGS. 10-13, the additional safeguards to prevent seri
ous overcharge and to shut the system off in the event
that. either the battery or the charger is defective are
also included; thus, a maximum total time limit, a maxi
mum voltage limit, a negative change in voltage, and a
negative slope limit may all be included as appropriate.
positive whereas in FIG. 1, the change was from posi
tive to negative.
Thus, the entire description of the method of in?ec
tion point analysis as applied in connection with FIGS.
1—9 can be converted to a method of in?ection point
analysis for the constant voltage case by changing the
word “voltage” to “current” and by reversing all words
such as “increasing", “decreasing”, positive”, “nega
tive”, etc.
Similarly, with regard to FIGS. 1043, the particular
The description of this invention as set forth above
batteries identi?ed there can be charged by the constant
has been given in terms of the battery analysis method
which applies when the state of charge of the battery is
voltage technique. In each case, the general method of
in?ection point analysis as set forth in the speci?cation
exactly corresponds to that which has already been
measured under “constant current” conditions. In addi
tion, it is possible to charge the battery in a “constant
voltage” mode, to measure the change in current with
the passage of time, and to apply similar methods of
in?ection point analysis to the resultant pro?le of
changing current with time. This technique involves the
selection of a constant voltage to be applied to the bat
tery by the charger; the voltage chosen is selected so
that the current which it applies to the battery during
the bulk of the charge time is reasonable on the basis of
the same parameters as described in the case of the
constant current charger, namely, the charge ef?ciency,
the cost, and the time required to fully charge a dis
charged battery. Once again, this application of con
stant voltage produces a known and predictable form
for the curve traced by the change in current with time.
Actually, the term “constant voltage” is applied
equally to systems in which the actual applied voltage is
constant throughout the charge period, to systems in
which the current is always measured when the voltage
is at a preselected value, or to systems in which a pulsat
ing applied voltage has a constant average and in which
the measured current is correspondingly averaged. All
of these systems produce a curve of current against time
which has the same general form and which may be
treated by means of the same in?ection point analysis;
accordingly, this pro?le is referred to herein as the
A primary benefit of the present invention is that any
normal battery, that is, any battery which is not defec
tive, can be changed at a relatively high rate. In using
previously known battery charging methods, it has been
necessary to limit the application of high rate charging
currents to batteries which are especially adapted to
accommodate the inadequate shut-off modes in use.
This is due to the fact that previous methods cannot
stop the fast charge current at the proper moment and
the various harmful effects previously noted can occur.
Only batteries designed to withstand these effects can
be used and even such batteries experience shortened
lives, etc.
In contrast, the method of the present invention pro
vides such precise control over the application of en
ergy to the battery that it can be used to fast charge
even those batteries which were previously intended for
charging only by slow rate methods.
The term “trickle charge” usually refers to a charge
rate such that the battery receives its full charge only
over a period of 12 to 24 hours. Thus, typical trickle
chargers apply a current of between 0.05C and 0.1C. In
accordance with previous methods, the terms “fast
charge” or “quick charge” are generally applied to
“current pro?le”.
rates in excess of 0.2C; that is, charge rates which would
In the particular case of a nickel-cadmium battery,
charge a battery in less than 5 hours.
the current pro?le is illustrated in FIG. 14. In fact, this
All batteries accept currents of the “fast charge”
curve is exactly the same in form as that shown in FIG. 45 level for limited periods of time. The upper limit for a
1 except that the entire curve is inverted. Thus, the
particular battery is governed by the current~accept
method of in?ection point analysis as applied to this
ance capability of the battery; that is, of its internal and
pro?le is exactly the same as has been described in con
external connections, and of its internal plates, and also
nection with FIG. 1 except that all of the pertinent
by its internal ion transit time. This level is generally
analyses regarding signs, direction of change, etc. are
given by the manufacturer. For example, sub-C size
reversed. Initially, the current decreases in a manner
nickel-cadmium batteries available from General Elec
corresponding to that in Region I in .which the voltage
tric can accept fast charge current at the 4C rate; lead
of FIG. 1 increased. This is followed by an interval in
acid batteries of the sealed type available from Gates
which the current decreases slowly; this is normally the
Energy Products, Inc. can accept fast charge current at
longest time interval and the one in which the major
the 0.3C rate.
increase occurs in the energy stored in the battery. This
Even though batteries could accept such fast charge
corresponds to the increasing voltage of Region II of
currents, presently known chargers are not capable of
FIG. 1.
shutting off the fast charge current at the proper mo
The in?ection point which must be identi?ed be
ment and even batteries which structurally could accept
tween this interval and the next Region of sharply de 60 fast rate currents can only be charged at the trickle
creasing current occurs at the same point in time as
charge rate. In general, any charge rate above the 5
point A in FIG. 1. However, it identi?es a change in the
hour rate (0.2C) has previously required a special bat~
sign of the second derivative of current from positive to
tery design.
negative whereas Point A in FIG. 1 identi?ed a change
Because of the accuracy with which the present in
in the sign of the second derivative of voltage from 65 vention determines the full charge level, the present
negative to positive. Similarly, the in?ection point be
charging method permits the use of fast charge currents
tween Regions III and IV is now identi?ed as that at
with many batteries which could previously be charged
which the second derivative changes from negative to
only by slow, trickle charge rates. This is particularly
true in the categories of nickel-cadmium batteries and
lead acid batteries which predominate among the re
chargeable battery couples presently available.
Thus, the present method permits essentially all of
battery characteristic selected for analysis. While the
present description has been directed particularly to the
voltage or current, pro?les or other characteristics,
particularly electrical characteristics might also be ana
lyzed. It is noted that this pro?le may also vary with
other battery conditions; in fact, as previously de
scribed, the analysis of this invention partially depends
nickel-cadmium batteries presently in use by consumers
to be recharged in a time on the order of 1 hour. Lead
acid batteries of the gal type can be charged in a time on
the order of 2 hours; those of the liquid type can be even
more quickly charged.
In general terms,,the present invention permits the
application of a high rate; that is, a rate in excess of 0.2C
and up to the rated current acceptance level of the
battery; normal batteries so charged by the system of
the present invention will receive a full charge and will
not be damaged.
, Another set of variations comprises the particular
on the fact that other battery conditions affect the pro
In addition to the extremely precise method of in?ec
tion point analysis as hereinbefore described, the pres
ent invention also encompasses the analysis for other
critical points in the pro?le of variation with time of a
15 characteristic of the battery which changes with the
energy level stored in the battery. In addition, there
fore, to in?ection point analysis, the present invention is
In the case of nickel-cadmium batteries, the in?ection
point analysis described above brings a battery to essen
also in part directed to improvements in method and
apparatus for charging batteries which relate to detailed
tially 100% charge. Thus, when the second in?ection
analyses involving combinations of such factors as limit
analyses of the pro?le of battery characteristics, the
point has been reached, the charger can shift into a
maintenance mode in which short pulses of high rate
charging current are applied periodically to compensate
for self-discharge. For example, a 1C current may be
applied for 15 seconds every 6 hours. Other mainte
nance cycles might be used if desired.
ing value, slope, and passage of time. By analysing the
pro?le of the particular characteristic for the battery
under charge, particular combinations of these events
may be identi?ed and used by those familiar with batter
ies and the art of battery charging to provide improved
techniques of fast battery charging without departing
from the spirit of the present invention.
In actual practice, repetitive charging of the battery
to exactly the second in?ection point may cause minute
reversible degradation because this point occurs a small
1 so that cut-off occurs in accordance with block 145 of
FIG. 6 which reverses the degradation.
‘In addition, the present invention presents numerous
subcombinations of this method which have not previ
ously been known; the many variations of these combi
nations which will readily occur to those familiar with
the battery and battery charging art are also intended to
be included.
Particular emphasis has also been placed on the
charging of nickel-cadmium batteries and lead acid
‘batteries in view of the importance of these couples.
To completely prevent even the possibility of such
The specific methods perfected for charging such bat
fraction of a percentage point below 100% charge. This
degradation may be reversed when the battery is left on
maintenance or when the operator, occasionally, places
the battery on charge even though it is not discharged.
This drives the voltage slightly into Region V of FIG.
degradation, a surcharge current of 0.1C can be applied
teries are also fully within the contemplation of the
for a few hours after the second in?ection point has 40 present invention.
been reached. The above-described maintenance cycle
Finally, a speci?c apparatus has been disclosed for
may then begin.
performing the method of this invention. A great many
In the case of lead acid batteries, as has previously
obvious variations of this apparatus will be readily ap
been discussed, an interval of low rate charging may be
parent which correspond generally to the alternative
useful to completely charge the battery; thereafter, an
methods described. It is fully intended that the appara
appropriate maintenance mode is used to compensate
tus claims in this application be extended to cover all
for self-discharge. In other battery couples, other ?nish
such alternative embodiments of this basic apparatus.
ing techniques may be utilized as appropriate.
We claim:
1. A method of rapidly and ef?ciently charging a
battery of the type having characteristic associated
The foregoing speci?cation describes a battery
therewith that varies with the state of charge of the
charging method which basically utilizes the in?ection
battery and in which the characteristic varies with time
point analysis method to identify very precisely signi?
during charging to exhibit a plurality of in?ection
cant points in the variation of the electrochemical en
‘points prior to the battery attaining substantial full
charge, the method comprising the steps of:
supplying electrical energy to the battery for charg
ergy in a battery during its charge cycle. Accordingly,
the appended claims are broadly directed to this method
and are intended to include all variations of this method
ing thereof;
as may be obvious to those skilled in the art.
monitoring said characteristic drawn by the battery
Among the many possible variations, it should be
noted that the above apparatus particularly described 60
analyzing the variation of said monitored characteris
has made use of an approximation technique for deter
mining the occurrence of an in?ection point. It is, of
course, fully within the contemplation 'of this invention
to use this or other approximation techniques for locat
ing critical points in a pro?le, or to provide a circuit 65
last in?ection point exhibited prior to the battery
attaining substantial full charge; and
controlling the supply of electrical energy of the
which is capable of directly monitoring the second
derivative for a change in sign. Similar variations may
also be used with regard to other parametric pro?les.
during charging;
tic with time to determine .the occurrence of the
battery on the basis of the so-determined occur
2. A method of rapidly and ef?ciently charging a
battery of the type in which the voltage characteristic
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