A multi-cell battery protection system is described wherein each cell has its own individual protective circuit. The protective circuits consist of a solid state comparator unit and a high current switching device such as a relay. The comparator units each continuously monitor the associated cell and when the cell voltage either exceeds a predetermined high level or falls below a predetermined low level, the relay is actuated whereby a bypass circuit is completed across the cell thereby effectively removing the cell from the series of cells

Nagle, W. J.

Thomas, R. D.

English

NASA Technical Reports Server

United States Patent b91 [I11 4,061,955 
Thomas et al. 1451 Dec. 6, 1977 
1541 MULTI-CELL BATTERY PROTECTION - .  
SYSTEM 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No.: 
[22] Filed: 
r511 Int. CI. ..... 
Ralph D. Thomas, Cleveland; Nagle, 
William J., Avon Lake, both of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
687,822 
May 19,1976 
............................................ HOW 7/04 
1.521 U.S. Cl. .......................................... 320/6; 320/15; 
320/ 18; 320/40 
(581 Field of Search ................... 320/2, 15, 17, 18, 40, 
320/48,6, 7, 8, 13; 340/249 
- -  
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,343,058 9/1967 Deschamps et al. .............. 320/40 X 
4 
3,348,117 10/1967 Howden ................................. 320/18 
3,496,442 2/1970 Carlisle .................................. 320/18 
3,872,457 3/1975 Ray .................................... 320/48X 
Primary Examiner-Robert J. Hickey 
Attorney, Agent, or Firm-N. T. Musial; J. A. Mackin; 
John R. Manning 
1571 ABSTRACT 
A multi-cell battery protection system is provided 
wherein each cell has its own individual protective 
circuit. The protective circuits each comprise a solid 
state comparator unit and a high current switching 
device such as a relay. The comparator units each con- 
tinuously monitor the associated cell and when the cell 
voltage either exceeds a predetermined “high” level or 
falls below a predetermined “low” level, the relay is 
actuated whereby a bypass circuit is completed across 
the cell thereby effectively removing the cell from the 
series of cells. 
8 Claims, 1 Drawing Figure 
f 
* V  c 
https://ntrs.nasa.gov/search.jsp?R=19780006682 2020-03-20T13:00:52+00:00Z
U.S. Patent Dec. 6, 1977 4,06 1,955 
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though it has other applications, the device of the inven- 
MULTI-CELL BATITRY PROTECTION SYSTEM tion is particularly adapted for use in space flight appli- 
cations and, to this end, the individual protective cir- 
cuits are small, compact and lightweight particularly as ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 5 compared with the relatively large and bulky meter- 
ees of the United States Government and may be manu- relay units which are conventionally used. As noted 
factured or used by or for the Government without the hereinbelow, the protective circuits each comprise a 
payment of any royalties thereon or therefor. solid state voltage comparator and a higher current 
switching unit such as a relay and the two units can be 
10 combined into a single module which can be directly FIELD OF THE INVENTION 
The present invention relates to protective Circuits mounted on each cell,ofthe battery part ofthe cell or 
for batteries and more particular, to a protective system battery case construction. 
which includes individual protective Circuits for each According to a preferred embodiment thereon, a 
cell of a battery. multi-cell battery protection system of the invention 
15 comprises a plurality of protective circuits equal in 
number to the number of cells of the battery, each pro- 
energy problems has lead to considerable research with and each a solid state circuit, 
of energy sources. One specific area of interest is that of 20 and the cell voltage with a predetermined 
and, in particular, increasing the life of such batteries for voltage level or limit and for generating an output 
nal when the cell voltage is out of limits, i.e., above the both terrestrial and space applications. 
batteries in particular, require close monitoring to make 25 corresponding to the high current switching unit re- 
cells thereof are operative. Moreover, the monitoring question responsive to the output signal from the com- or protective circuitry utilized for this purpose should 
be as parator circuit. The control unit preferably comprises a being totally reliable. For example, the use of meter- 3o relay which is connected such that the out-of-limits cell 
relay type monitoring units in large quantities so 8s to is open circuited and effectively replaced preferrably by 
protect each cell under test is impractical in of a shorting bar or alternatively a cell voltage simulation 
cost and space requirements. Further, in many in- circuit in the series of cells making up the battery. As 
stances, totai protection has not been &&able with- soon as the cell returns to an in-limits condition, the 
computer equipment. the battery, regardless of whether the battery is in a 
Reference is made to U.S. Pat. Nos. 3,305,754 (Oakes charging Or mode Of operation* Thus* no 
et d); 3,470,441 (Ford et al); 3,707,664 (Bh) and cell in the battery is ever permitted to be driven beyond 
3,806,906 (Young), for examples of battery charging the predetermined limits. 
and monitoring systems of interest. The Ford et al pa- 40 The comparator circuit preferably comprises a differ- 
tent discloses an automatic formation cycler and con- ential amplifier connected across the corresponding 
troller for electrochemical cells wherein an electrome- and and second each having one 
chanical stepping switch is used to sequentially connect input connected to the output of the differential ampli- 
the individual cells into a testing circuit wherein the fier. The second input Of the first comparator is con- 
output of the cell is compared with the high and low 45 nected to a potentiometer which Provides a Predeter- 
voltage levels during charging and discharging. The lllhed “high” reference Voltage. S h h d Y ,  the second 
switch sequentially routes voltage samples from each input Ofthe second comparator is Connected to a further 
individual cell to a single voltage detector which thus potentiometer which provides a predetermined “low” 
monitors all of the cells in sequence. n e  patent is reference voltage. A driver transistor connected to the 
811 example of systems wherein individual voltage ms i -  50 comparator outputs is triggered when an out-of-limit 
tive relays are used, the relays in this case being em- voltage is sensed bY either comparator. 
ployed to monitor selected cells having a charge capac- Further comparing the Protective system of the in- 
ity significantly lower than the non-monitored cells. vention with prior art battery chargers and monitors, it 
The Young patent discloses a system which indicates is noted that use of an ekmomechanical stepping 
the failure to properly conduct current of any cell in 55 switch, such as disclosed in the Ford et al patent dis- 
each bridge of an electric power converter, while the cussed above, is disadvantageous from several stand- 
Oaks et a1 patent discloses a charging apparatus for points. For example, a system employing a stepping 
multi-cell batteries which employs a stepping switch switch samples the cell voltages at a rate corresponding 
scanner and meter relay unit to sense individual cell to the stepping rate of the switch and the number of 
voltages. 60 cells in the battery, rather than providing continuous 
uninterrupted protection. Moreover, the noise levels 
associated with such stepping switches can trigger a SUMMARY OF THE INVENTION 
In accordance with the present invention, a protec- switching level at a point which is higher or lower than 
tive system for a battery is provided which serves to a critical set-point. Additionally, the system of the in- 
extend the life of the battery for both terrestrial and 65 vention can be set to continuously switch a cell into and 
space applications. The system includes a separate pro- out of the circuit (Le., control the cell voltage relative to 
tective circuit for each cell of the battery so that contin- a given set-point) rather than simply locking that cell of 
uous, totally uninterrupted protection is afforded. Ai- the circuit. Further, a timing circuit prevents exceSSive 
BACKGROUND OF THE INVENTION 
n e  heightened concern in recent years regarding tective circuit being associated with an individual cell 
connected across the corresponding cell, for sensing 
upper voltage level or limit and a predetermined lower 
respect to energy conservation and savings in the 
improving primary sources such as batteries 
Batteries in space flight applications~ and sealed upper level or below the lower level, and a control unit, 
they are in good working condition and that al’ ferred to abve,  for controlling bypassing of the cell in 
and lightweight as possible while 
out the necessity of resorting to highly sophisticated 35 bypass is removed and the cell is returned to service in 
4,061,955 
3 4 
relay contact wear and “chatter,” in the control mode 
of the invention. 
Other features and advantages of the invention will 
be set forth in, or apparent from, the detailed descrip- 
tion of a preferred embodiment found hereinbelow. 
The switching units 20 are also identical in construc- 
tion and switching unit 201 will be considered as exem- 
plary. Switching unit 201 includes a relay coil 72, which 
is connected to output terminal 70 of comparator unit 
5 10, and which controls single-pole, double-throw relay 
contacts 741 as is illustrated by the dashed line indicating 
a mechanical connection between the relay contacts 
741 and the armature of coil 721. 
Relay contacts 741 are connected in series with a 
10 bypass circuit 801 which is connected across cell CI. 
Bypass circuit SO1 is normally open, with coil 721 de- 
energized and relay contacts 741 in the open position as 
illustrated. When coil 721 is energized, relay contacts 
The single figure in thehwings  illustrates, in a sche- 741 are closed and bypass circuit SO1 is connected in the 
matic manner, a preferred embodiment of the battery 15 system, thereby removing cell C1 from the circuit and 
protection system of the invention. It will be under- replacing the cell in the series of cells with a short cir- 
stood that the protection system can be used with a cuit. Similar bypass circuits are provided for each of the 
battery having any number of cells and a generalized other cells, as is indicated by circuits SO2 and SON. Al- 
“N-cell” system is illustrated. ’ I  though the by-pass circuit 801. . . 8O~can simply com- 
The protection system basically comprises a plurality 20 prise a shorting bar, the circuit may include a cell volt- 
of comparator units, collectively denoted 10, and a age simulating circuit (CVSC) comprising a diode 901, 
plurality of switching units, collectively denoted 20, connected in parallel with a serially connected diode 
both equal in number to the cells of the battery. The 901 and resistor 9&. This circuit prevents excess charg- 
cells are denoted C1, Cz . . . CNand thus cell C1, is pro- ing current from being supplied to the cells which make 
tected by an individual comparator unit lo1 and an indi- 25 up a battery when one or more of the cells is by-passed 
vidual switching unit 201, cell C, is protected by an or removed from the battery. This is particularly impor- 
individual comparator unit 1O2and an individual switch- tant where the charging current is tapered or reduced as 
ing unit 2O2, and so on, up to the general case where cell the total battery voltage approaches its normal value. In 
CN is protected by an individual comparator unit 1 0 ~  such a situation, if one of the cells is bypassed, the total 
and an individual switching unit 20,. 30 battery voltage will decrease. This causes the battery 
Cells C1, Cz . . . CN are connected across a battery charger to increase the charging current at a time when 
charging and/or loading circuit indicated by block 30. the charging current should be decreasing. 
The system is powered from a power supply 40 which With the cell simulating circuit, if the bypass contacts 
converts the input power obtained from the system SO1 close while the battery is being charged, a voltage 
power bus or from an external power source into suit- 35 will appear across resistor due to charging current 
able supply voltages for the comparator units 10 and therethrough. The resistance of the resistor is selected 
switching units 20. For some applications, wherein, for so the voltage thereacross is close to that of the re- 
example, power is not readily available, it is preferable moved cell although this is dependent on charging cur- 
that the system power supply being powered directly rent at the time the cell is bypassed. Thus, removal of 
from the battery itself. 40 the cell causes only a relatively small change in total 
Comparator units 10 are identical in construction and battery voltage so that charging current does not in- 
hence only comparator unit lo1 has been illustrated. crease excessively. 
Comparator unit lo1 includes a fmt operational ampli- During times when the battery is supplying current to 
tier 50 which is connected as differential amplifier a load, the current passes through diode 9 0 1  with negli- 
across the positive and negative terminals of cell C1. 45 gible voltage drop if bypass contacts 901 are closed. A 
The output of differential amplifier 50 is connected to cell voltage simulating circuit as just described is prefer- 
the positive input of a fust operational amplifier 52 and ably provided for each cell so that, as illustrated, the 
to the negative input of a second operational amplifier system includes N circuits having diodes 901 . . . 90N, 
54. Operational amplifiers 52 and 54 function as voltage 911. . . 9 1 ~ a n d  resistors 9Z1. . . 92N, where N is equal to 
comparators, with comparator 52 comparing the output 50 the number of cells. 
of differential amplifier 50 with a “high” set-point as The overall operation of the system will be evident 
determined by a fust potentiometer 56 and comparator from the foregoing. Comparator 10 provides continu- 
54 comparing the output of differential amplifier 50 ous monitoring of the individual cells associated there- 
with a “low” set-point as determined by a second poten- with. When a cell produces an out-of-limit voltage, this 
tiometer 58. Potentiometers 56 and 58 are connected 55 is detected by the corresponding comparator 10, and 
through a resistor 60 to the positive supply and a zener the associated switching unit 20 is actuated so that the 
diode 62 Connected between the positive supply and cell in question is bypassed. When the cell voltage re- 
ground serves in stabilizing the supply. The outputs of turns to an in-limit level, switching unit 20 is de-ener- 
comparators 52 and 54 are connected through respec- gized and the bypass is removed so that the cell is re- 
tive diodes 64 and 66 to a driver transistor 68, the col- 60 stored to operation. 
lector of which is connected to the output terminal 70 of To provide isolation between the drive for the 
comparator unit 10. When the voltage across cell C1, as switching units and the comparator units, the output of 
detected by differential amplifier 50, is greater than the the driver 68 may be coupled to winding 72 through the 
predetermined “high” set voltage of potentiometer 56 combination of light emitting diode (LED) and a photo- 
or lower than the predetermined “low” set-point of 65 conductor. 
potentiometer 58, transistor 68 will be switched on by Voltage comparator 101 can readily be implemented 
the resultant output of comparator 52 or 54 and an using integrated circuit techniques and hence can be 
output signal will appear at terminal 70. made to be very small and compact so that the circuit 
DESCRIPT1oN OF THE 
The single F b U R E  in the drawings is a schematic 
circuit diagram of the multi-cell battery protection SYS- 
tem of the invention. 
DESCRIPTION O F  THE PREFERRED 
EqBQDIMENTS 
f 
5 
4,06 1,955 
6 
can be mounted directly on th corresponding cell. Thus, 2. A protection system as claimed in claim 1 wherein 
each cell is a complete self-protecting unit with respect each said comparator means comprises an operational 
to electrical parameters in question. amplifier connected as a differential amplifier across the 
It will be appreciated that the protective system of associated cell, first and second operational amplifier 
the invention permits a battery to be discharged much 5 comparators each having a first input connected to the 
“deeper,” i.e., to a greater extent, without the danger of output of said differential amplifier, the second input of 
cell reversal and consequent explosion. Such a deeper said first comparator being connected to a first voltage 
discharge increases the useful energy that is available source providing said predetermine$ upper voltage 
from a battery and therefore reduces the relative weight level and the second input of said second comparator 
thereof. 10 being connected to a second voltage source providing 
Although the invention has been described relative to said predetermined lower voltage level. 
an exemplary embodiment thereof, it will be understood 3. A protection system as clairhed in claim 2 wherein 
that other variations and modifications can be effected said first and second voltage so#ces comprise first and 
in this embodiment without departing from the scope second potentiometers. 
and spirit of the invention. 4. A protection system as clahed in claim 3 wherein 
We claim: said potentiometers are connected to a common supply 
1. A protection system for a battery having a plurality terminal, said system further comprising a zener diode 
connected between said supply terminal and ground. 
a plurality of protective circuits equal in number to 5. A protection syswm as claimed in claim 2 further 
the number of said cells, each said circuit being 20 comprising a transistor connected to the outputs of said 
associated with an individual cell and each said comparators for controlling actuation of said control 
circuit comprising solid state comparator means, means. 
connected across the corresponding cell, for con- 6. A protection system as claimed in claim 1 further 
tinuously sensing and comparing the cell voltage comprising means for connecting said voltage compara- ~ 
with a predetermined upper voltage level and a 25 tor means to said cells so as to provide power for said 
predetermined lower voltage and for generating an voltage comparator means. 
output signal when said cell voltage is above said 7. A protection system as claimed in claim 1 wherein 
upper level or below said lower level, a normally said comparator means includes a drive transistor which 
open bypass circuit for bypassing said cell, control is switched on by said output signal and said control 
means responsive to said output signal for complet- 30 means comprising a relay energized by said drive tran- 
ing said bypass circuit to cause bypassing of said sistor. 
cell when the cell voltage is above said upper level 8. A protection system as claimed in claim 7 wherein 
or below said lower level, said bypass circuit com- said relay includes a coil connected in series with said 
prishg oppositely poled diodes connected in pard- drive transistor and normally open contacts connected 
le1 and a resistor connected in series with one of 35 in series with said bypass circuit. 
said diodes. * * * * *  
15 
of cells, said system comprising: 
, 
(4 II 
40 
45 
50 
55 
65 


Multi-cell battery protection system

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