CA1043870A - Dual battery charge control - Google Patents

Abstract

DUAL BATTERY CHARGE CONTROL

ABSTRACT OF THE DISCLOSURE

Two series-connected batteries are connected across the power and ground terminals of an alternator and a silicon rectifier selectively connects said power terminal to the junction between the batteries. A turn-on control circuit for the silicon controlled rectifier is connected across the battery providing the higher voltage output to effect conduction of the silicon controlled rectifier when the voltage drop across said battery reaches a predetermined value, whereby to direct charging current from the alterna-tor only through the battery providing the lower voltage output. A turn-off control circuit for the silicon con-trolled rectifier also may be provided to connect the series batteries to the power input of a voltage regulator to effect deactivation of the alternator and silicon controlled recti-fier when the voltage drop a-cross the higher voltage output battery decreases a predetermined amount with respect to the voltage drop across the lower voltage output battery, the turn-off control circuit also functioning to activate the voltage regulator, alternator and silicon control rectifier when the voltage across the lower voltage output battery starts to drop, thereby re-establishing charging through both batteries.

Description

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- This in~ention relates t~o battery charging, and more particularly to the charging of: batteries connected together in series.
Many electrical systems utllize batteries connected in series to provide two output voltages. For example, diesel ~' powered trucks, marine equipment, and others utilize a 24 -volt or higher supply for starting engines, etc., but require -, onlyjl2 volts for the remaining electrical components.
;, In such systems there is presented the problem of pro-viding proper charging of each battery, since theyrequire different amounts of charge. For example, the battery pro- -;
viding the higher voltage output for engine starting generally is used much less than the othe~ and therefore it requires only a few minutes of charge to replace the 109s. The battery providing the lower voltage output also ls used for engine starting, but has the added demand of the remaining electrlcal system, and therefore it requires more eharge.
~t~ T~us, ~or example, if a regulated 24 volt charge ~rom an alternator is applied a~ the positive terminal of the higher voltage output battery, the latter becomes ~ully charged be~ore the lower voltage output battery. However, the voltage regu-~i ~ lator sees only the voltage drop across the series-connected , ii ~ ~, ...... .
batteries, and there~ore allows the alternator to continue charging until said voltage is satisfied. As a result~ the higher voltage battery is overcharged and the lower voltage output batte~ is undercharged, causing premature damage to othbQtteries.

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' Efforts have been made heretofore to achieve proper charging of each battery in dual battery systems. For example switching systems have been provided for connecting the batt- ;
~ eries in series for starting engines, etc., and for connect-', inging the batteries in parallel for charging. However, the ' :
additional electrical resistance contributed b~ the switch results in the higher voltage output battery being maintained '' ~ - , .. ..
in an undercharged condition. The use of two alternators''~ ~' ', in an attempt to balance the loads, also has been found '~, unacceptable. 'Special alternators of complex and costly, , ', , circuitry and,physical design have been found to be econom- ~ ' . :
,!,j ically impracticable. , ,, Equally unsatisfactory have been the attempts to cir- ', i~ cumvent the battery charging problem by using high powered ' ~ 12 volt starter systems, or by utilizing straight 24 voltage '~ ;
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~ systems,for charging and for all other components o the , '~ , 't' ~
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~;';; ~ SUMMARY OF THE INVENTION
,~ In its basic concept, this inven~ion providesa charge , control for series-connected batteries in which the voltage drop across the battery providing the higher voltage output ~ is utilized at a predetermined,value to switch the oharging ,, ' currant from the series-connected batteries to only the I `~ , battery providing the lower voltage outpu~.
It is by virtue o~ the foregoing basic concept that the principal objective of this invention is achie~ed; namely, ,, to overcome the aforementioned difficulties and disadvantages ' ' o~ prior c~arging systems.
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Another obvect of this invention is the provision of a dual battery charge control which is operable with conven-tional generators and alternators as well as with conventional voltage regulators.
Still another objective of this inven~ion is the pro-vision of a dual battery charge control which functions automatically to achieve proper charging of each battery in a dualbQttery system. ~-A further obJect of this invention is the provision of a dual battery charge control which is of simplified con- -i struction for economical manufacture. -~
;,~ The foregoing and other objects and advantages of this -invention will appear from the following detailed description, taken in connection with the accompanying drawings of pre-ferred embodiments.
Fig. l is a schematic electrical diagram showing asso-ciated with series-connected batteries and a conventional alternator a dual battery charge control embodying the features of this invention. ;
Fig. 2 is a fragmentary schematic electrical diagram showing a modification o the charge control of Fig. 1 to accommodate use of a conventional original equipment voltage t~ regulator.
I; Figs. 3 and 4 are fragmentary schematic electrical dia-i~ gr~ms show.ing a modification of a conven~ional voltage regu-lator circuit and alternative connections thereof ~o the battery and alternator system for association w;th the charge control of this invention.

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DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1 of the drawings, two batteries 10 and 12 are shown connected together in series. The nega-tive terminal of battery 10 is connected to common ground, the positive terminal of said battery and the negative terminal of the battery 12 are connected together at a -common junction 14. An electrical conductor 16 extends from this junction to supply an electrical system with the lower voltage output from battey 10. The positive terminal of the .,~ . , . .... ~
other battery 12 is connected to an electrical conductor 18 ! which supplies an engine starter or other load with the higher voltage output provided by the serles-connected ~ ;~
batteries. Thus, for example, with each battery providing a ~;~ 12 volt output, the conductor 16 provides 12 volts to an electrical system, while the conductor 18 provides 24 volts . j . .
~ to an engine starter or other electric load.
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~ Figo 1 also illustrates a convantional alternator 20 : which is mechanically activated by a vehicle or other drive engine, as by coupling thereto through a belt and pully arr-angement, as will be understood. It will be appreciated that ., : ..
the alternator may be replaced by a conventional generator.
;~ The alternator illustrat~d i9 provided with a ground terminal 22 for connection to common ground; a power output terminal ~ - 24 ~or delivering charging current to the batteries; and a ¦ ~ield termlnal 26 ~or connection of power ~rom a voltage regulator 28.
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The voltage regulator illus~rated is of conventional design and includes the transistor 30 which is biased normally ,~: '. .
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on, the transistor 32 which is biased normally o~f, the res-istors 34, 36, 38, uncontrolled diode 40, zener diode 42, and voltage detecting resistors 44, 46 and 48. The voltage regulator is provided with a ground terminal 50 for connection 1;
to common gr~nd; a field supply terminal 52 for connection to ~-;
the field windings of the alternator; a power input terminal 54; and a sensing signal input terminal 56 for connection of an external sensing signal.
Ordinarily, the sensing signal terminal56 of convention-al, original equipment regulators is not available for external connection. Accordingly, the charge control circuit and voltage regulator circuit of Fig. 1 are manufactured as -an integral unit.
The power output terminal 24 of the alternator is co~-nected to the positive terminal of battery 12 through an uncontrolled diode 58. This diode functions upon attainment of a predetermined voltage at the output terminal 24 to conduct charging current to the positive terminal of battery . . .
12, thence ~hrough said ba~tery to the common junction 14, .
~ thence through battery 10 to common ground.
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'~ In accordance with this invention, means is provided for 1: . . . .
switching the output terminal 24 o~ the alternator to the common junction 14 upon attainment o~ a predetermined voltage drop acro~s tha battery 12 providing the higher voltage output, whereby ~o direct charging current only through the battery 10 providing ~he lower voltage output. In the general con- ; .
cept of this invention, this i9 provided by ele~trically actuated switch means which removably connects the output .~ .
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of the generating means to said common junction, and by electrical switch actuator means which is connected across ... .
the battery providing the higher voltage output and which is responsive to a predetermined voltage drop across said battery to activate the switch means to connect the output of the generating means across only thebattery providing the lower voltage output.
In the specific embodiment illustrated in Fig. 1, the electrically actuated switch means is provided by a silicon controlled rectifier 60 which interconnects the power output terminaI 24 of the alternator and t~e co~mon junction 14 between the~atteries. The silicon eontrolled rectifier is normally off; hence, the switch means is normally open. ;~
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The electrical switch actuator means or turning on the ~j~ silicon controlled rectifier 60 includes the voltage detecting resistors 62, 64 and 66, the zener diode 68, the transistor 70 which is biased normally off, and the resistor 72 w~ich inter- ;
connects the transistor collecDr and the gate of the silicon controlled recti~ier 60.
The charge control of this i~vention also may include a second electrical swltch actua~or means for turning off the silioon controlled rsctifier 60 ~returning the switch means to its normally open eondition). In Fig. 1 ~his turn off control includes the transistor 74 which is biased normally off, the ,¦ resistor 76 which lnterconnects the transistor collector and the sensing signal terminal 56 of the voltage regulator, and ¦i~ the resistors 78, 80 and 82 which, by connection across the ~, ~ batteriss 10 and 12, form therewith a bridge network.
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The operation of the charge control illustrated in Fig.
l is as follows: With the alternator 20 being driven mechani-- -cally by the engine, the normally conducting transistor 30 of the voltage regulator provides power through terminals 52 and 26 to the alternator fields, thereby producing charging current at the alternator output terminal 24. Since the silicon control rectifier 60 is not conducting, charging ~
current from the output terminal cannot get through to the ; ~ -common junction 14. Accordingly, voltage continues to rise at the output terminal until the diode 58 conducts. There-upon charging current is conducted through the series- .
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, connected batteries 12 and 10 to common ground. Both batteries thus are charged.
In the normal operation of the voltage regulator, when the voltage across the battery~10 providing the lower voltage output reaches a predetermined value, as sensed by the voltage regulator resistors 4~ 46 and 48, zener diode 42 fires, caus-ing the normally off transistor 32 to conduct. The normally on transistor 30 thus is turned off, causing the alternator 1~ ~ ~ fields to weaken and the output voltage to drop. When the ~, voltage across the battery 10 provlding the lower voltage output drops slightly, zener diode 42 ceases conduction, ther~ , ;
by turning off the transistor 32 and turning on translstor 30, l~ allowing the alternator output voltage to be controlled.
jl ~ ! When the voltage across the battery 12 providing the higher voltage output reaches a predetermined value, as sensed by resi$tors 627 64 and 66, zener diode 68 is caused to ~ire, turning on transistor 70. Activation of this transistor .

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effects activation of the silicon controlled rec-tifier 60. ~
Charging current thus is directed from the output terminal ' 24 of the altern~r to the common junction 14. Since the voltage at the output terminal 24 drops to a predetermined ' value lower than the voltage at the positive terminal of ; ' battery 12, the diode 58 ceases to conduct. Charging current ' through the battery 12 providing the higher voltage output thus is stopped. Charging current from the output terminal 24 thereupon is directed through the activated silicon'control- '' led rect~ier 60 to junction 14 to continue charging the battery 10 providing the lower voltage output. This occurs l because, thoug'h the voltage at the base of'trans~istor 70 drops to turn the latter off, thereby removing the control signal from the gate of the silicon control rectifier 60,~the latter is conducting direct current and there~ore continues in its~abtivated state.
When the voltage at the output terminal 24 of the alter- r nator drops to a predetermined value relatl~e to the common junction 143 current sto*s flowing.
When the voltage across the battery 12 is providing the higher voltageoutput drops (the voltage across the battery 10 providing the lower voltage output remains at regulated vol-tage), the base of transistor 74 goes negative to a predeter- ' ' ' m'ined value wlth respect to the common junction 14, as d~ter- '' ., ~
mlned by the bridge network, transistor 74 is activated. This in turn, effects firing o~ zener diode 42, ther~y acti~ating transistor 32 and deactivating transistor 30. The alterna- ' ~ ~ tor output thus is stopped, ~hereupon ~he silicon controlled ' ' ,;' ,: ~ . ' :
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When the voltage across the battery ~ providing the lower voltage output starts to drop, the base of transistor 74 become more positive with respect to the common junction 14, whereupon transistor 74 is turned off. The voltage regulator thereupon assumes control and the voltage at the I . alternator output terminal 24 rises until diode 58 conducts, whereby once again to.re-establish the series charge through the batteries 10 and 12.
It will be understood that the turn-off control for the silicon controlled rectifier may be omitted for some appli- .. :
cations as, for example, when the battery providing the -:;.
higher voItage output is used only for starting and engine ; .
j - and charging is not.needed until after a subsequent start.
¦ : In such applications the silicon controlled rectifier.is ~ : tuxned off simply by stopping the engine. .
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.: ~ig. 2 illustrates a modification of the turn-off control .:.
for the silicon controlled rectiier, to accommodate the use of an original equipment voltage regulator 2Br, rather than incorporating a voltage regulator in the charge:control, as ;:
in Fig.. l. For this purpose a transistor 84 is interposed ~.
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between the collector of transistor 74 and the power input terminal 54 o~:the voltage regulator. Thus, when the voltage across the battery 12 providing the higher voltage output . . ~ .
drops, the base o~ txansistor 74 goes negativewith respect to the common junction 14, activating the transistor 7~. This effects deactivation of transistor 84 which is biased normal- , :
ly on. Deactivation o transistor 84 removes power input to.

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the regulator and effects deactivation of transistor 30, thereby stopping power to the alternator fields and deacti-vating the alternator and silicon controlled rectifier.
Fig. 3 illustrates a modification of the voltage regu-lator arrangement shown in Fig. 1. Thus, the conductor 86 interconnecting the resistors 36 and 44 in Fig. 1 is re-moved, and the voltage regulator power source is provided by the conductor 88 connected to the output terminal 24 of the :~
alternator. This arrangement is desirable for situations wherein more efficient charging at the higher potential is required, as for example when the battery 12 providing the higher volta6e ~tput su~ies other loads in addition to engine starting. Regulator senslng across batter~ 10, through ~ransistor 74, is utilized as in Fig. 1.
Fig. 4 illustrates a further modiication of Fig. 1 to accommodate the use of original equipment alternators 20~
which are designed for the nominal voltage~of the sum of the ,-two serles-connected batteries. In this arrangement, as in Fig. 3, the oonductor 86 interconnecting the resistors 36 and 44 in the voltage regulator o~ Fig. l is omitted. How-ever, power source for the voltage regulator is supplied ~ , . .
; through conductor 90 connected direc~ly to the higher voltage ~ ~ ~erminal of ~attery 12.
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From the foregoing it will be appreciated that the present invention provides a charge control of simplified and there-,~ . . . . ;
~ ~- fore economical construction whlch unctions effectively to ~ ~ .
provide precise charging o~ each of a pair o batteries con-nected together in séries, and is versatile in its applicabili~
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~ ty to a wide variety of conventional charging systems.~

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It will be apparent to those skilled in the art that various changes may be made in the type, number, and arrange-ment of components described hereinbefore~ For example, the control may be provided for use with positive ground systems, by substituting NPN type transistors for the PNP types illus- -trated, and reversing the polarities of the diodes. The original equipment voltage regulator 28' o Fig. 2 may be ~ ;~
integrated with the associated control circuitry, if desired.
The control may be associated with any desired combination of battery voltages other than tihe lZ volt batteries 10 and 12 described. For example, with battery 10 being 12 volts, battery 1~ may be 6 volts to provide a total of 18 volts; ~-20 volts to provide a total o~ ~ volts; 24 volts to provide a total of 36 volts; and many other combinations. These and , other changes may be madé without dieparting from the spirit of this invention. -, ~,, . .
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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A charge control for a pair of batteries connected in series across electrical generating means, comprising:
a) electrically actuated switch means arranged for removably connecting the output of the generating means to the junction between the series-connected batteries, b) electrical switch actuator means arranged for connection across the ungrounded battery and responsive to a predeter-mined voltage drop across said battery to activate the switch means to connect the output of the generating means across only the battery providing the lower voltage output, and c) said switch means comprising a silicon controlled rectifier and the actuator means comprises a transistor switch circuit connected to the silicon controlled rectifier gate and operable at said predetermined voltage drop to activate the silicon controlled rectifier.

2. The charge control of claim 1 including second electrical switch actuator means arranged for connection across the series-connected batteries and responsive to a predetermined voltage drop across the battery providing the higher voltage output to deactivate the switch means.

3. The charge control of claim 2 wherein a voltage regulator is associated with the generating means for controlling the output of the latter, and the second electrical switch actuator means is responsive to said predetermined voltage drop across the battery providing the higher voltage output to deactivate the voltage generator, generating means and switch means.

4. The charge control of claim 3 wherein the second electri-cal switch actuator means is also responsive to a predetermined voltage drop across the battery providing the lower voltage out-put to activate the voltage regulator and generating means and re-establish charging through the series-connected batteries.

5. The charge control of claim 4 wherein a) the switch means comprises a silicon controlled rectifier and the first named actuator means comprises a transistor switch circuit connected to the silicon controlled rectifier gate and operable at said predetermined voltage drop to activate the silicon controlled rectifier, and b) the second electrical switch actuator means comprises a transistor switch circuit connected to the voltage regulator and operable at the predetermined voltage drop across the battery providing the higher voltage output to deactivate the voltage regulator, generating means and said silicon controlled rectifier, and also operable at a predetermined voltage drop across the battery providing the lower voltage output to activate the voltage regulator and generating means to re-establish charging through the series-connected batteries.

6. The charge control of claim 4 wherein the voltage regu-lator has a power input terminal arranged for connection to the junction between the series-connected batteries and a sensing signal input terminal arranged for connection to the second electrical switch actuator means.

7. The charge control of claim 4 wherein the voltage regu-lator has a power input terminal arranged for connection to the power output terminal of the generating means and a sensing sig-nal input terminal arranged for connection to the second electri-cal switch actuator means.

8. The charge control of claim 4 wherein the voltage regu-lator has a power input terminal arranged for connection to the higher voltage terminal of the series-connected batteries and a sensing signal input terminal arranged for connection to the second electrical switch actuator means.

9. The charge control of claim 4 wherein the voltage regu-lator has a power input terminal arranged for connection to the second switch actuator means.

10. The charge control of claim 2 wherein a) a voltage regulator is associated with the generating means for controlling the output of the latter, the voltage regu-lator having the power input terminal and a sensing signal input terminal, b) the switch means comprises a silicon controlled rectifier and the first named actuator means comprises a transistor switch circuit connected to the silicon controlled recti-fier gate and operable at said predetermined voltage drop to activate the silicon controlled rectifier, and c) the second electrical switch actuator means comprises a transistor switch circuit connected to the sensing signal input terminal of the voltage regulator and operable at said predetermined voltage drop across the battery provid-ing the higher voltage output to deactivate the voltage regulator, generating means and said silicon controlled rectifier, and also operable at a predetermined voltage drop across the battery providing the lower voltage output to activate the voltage regulator and generating means to re-establish charging through the series-connected batteries, the power input terminal of the voltage regulator being arranged for connection to the junction between the series-connected batteries.

11. The charge control of claim 2 wherein a) a voltage regulator is associated with the generating means for controlling the output of the latter, the voltage regu-lator having a power input terminal, b) the switch means comprises a silicon controlled rectifier and the first named actuator means comprises a transistor switch circuit connected to the silicon controlled recti-fier gate and operable at said predetermined voltage drop to activate the silicon controlled rectifier, and c) the second electrical switch actuator means comprises a transistor switch circuit connected to the power input terminal of the voltage regulator and operable at said predetermined voltage drop across the battery providing the higher voltage output to deactivate the voltage regu-lator, generating means and said silicon controlled recti-fier, and also operable at a predetermined voltage drop across the battery providing the lower voltage output to activate the voltage regulator and generating means to re-establish charging through the series-connected batteries.

12. A charge control device for external connection between first and second series connected batteries and the single output terminal of a voltage regulated, DC output, generating means, com-prising:
a) blocking diode means normally connecting the output terminal of the generator to that pole of the first of the batteries re-mote from the junction between the two so as to charge the pair of batteries in series;
b) latchable electrically actuable switch means operable when actuated to establish a low resistant direct current path between the output terminal of the generating means and the junction between the first and second batteries;
c) electrical switch actuator means arranged for connection across the first of the batteries and responsive to a predeter-mined voltage drop across the first battery to actuate said switch means;
d) said switch means latching on after actuation to maintain said low resistance direct current path between the generating means output terminal and the junction between the batteries so as to charge only the second battery of the pair during the flow of dir-ect current in said path and irrespective of further voltage vari-ations in the first battery.