GB1585915A

GB1585915A - Dual battery charge control

Info

Publication number: GB1585915A
Application number: GB31216/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-07-26
Filing date: 1977-07-26
Publication date: 1981-03-11

Description

(54) DUAL BATTERY CHARGE CONTROL (71) I, RALPH ELLSWORTH SCHEIDLER, a citizen of the United States of America, of 7415 South East Johnson Creek Boulevard, Portland, State of Oregon 97206, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to battery charging, and more particularly to the charging of batteries connected together in series.

Many electrical systems utilize 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 only 12 volts for the remaining electrical components.

In such systems there is presented the problem of providing proper charging of each battery, since they require different amounts of charge. For example, the battery providing the higher voltage output for engine starting generally is used much less than the other and therefore it requires only a few minutes of charge to replace the loss.

The battery providing the lower voltage output also is used for engine starting, but has the added demand of the remaining electrical system, and therefore it requires more charge.

Thus, for example, if a regulated 24 volt charge from an alternator is applied at the positive terminal of the higher voltage output battery, the latter becomes fully charged before the lower voltage output battery.

However, the voltage regulator sees only the voltage drop across the series-connected batteries, and therefore 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 battery is undercharged, causing premature damage to both batteries.

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 batteries in series for starting engines, etc., and for connecting the batteries in parallel for charging. However, the additional electrical resistance contributed by 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 economically impracticable.

Equally unsatisfactory have been the attempts to circumvent the battery charging problem by using high powered 12 volt starter systems, or by utilizing straight 24 voltage system for charging and for all other components of the electrical system.

This invention provides a charging control for use with first and second batteries serially interconnected at a common junction to provide a high voltage output at the terminal of the first battery remote from the common junction and a low voltage output at the common junction and with an electrical generator having a D.C. output to provide charging current, said charging control comprising electrically actuated switch means for transferring one pole of the D.C. output from the high voltage output terminal to the common junction, the other pole of the D.C.

output remaining connected to the terminal of the second battery remote from the common junction, and electrical switch actuator means responsive to the voltage across said first battery for activating said switch means to connect the generator output across only the second battery instead of across both batteries when the voltage across said first battery reaches a predetermined value.

The present invention is further described hereinafter by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic electrical diagram showing associated with series-connected batteries and a conventional alternator a dual battery charging control embodying the features of this invention Fig. 2 is a fragmentary schematic electrical diagram showing a modification of the charging control of Fig. 1 to accommodate use of a conventional original equipment voltage regulator; and Figs. 3 and 4 are fragmentary schematic electrical diagrams showing a modification of a conventional voltage regulator circuit and alternative connections thereof to the battery and alternator system for association with the charging control of this invention.

Referring to Fig. 1 of the drawing, two batteries 10 and 12 are shown connected together in series. The negative terminal of battery 10 is connected to common earth, 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 battery 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 series-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 to an engine starter or other electric load.

Fig. 1 also illustrates a conventional alternator 20 which has a rectified output and which is mechanically activated by a vehicle or other drive engine, as by coupling thereto through a belt and pulley arrangement, as will be understood. It will be appreciated that the alternator may be replaced by a conventional generator. The alternator illustrated is provided with an earth terminal 22 for connection to common earth; a power output terminal 24 for delivering charging current to the batteries; and a field terminal 26 for connection of power from a voltage regulator 28.

The voltage regulator illustrated is of conventional design and includes the transistor 30 which is biased normally on, the transistor 32 which is biased normally off, the resistors 34, 36 and 38, uncontrolled diode 40, zener diode 42, and voltage detecting resistors 44, 46 and 48. The voltage regulator is provided with an earth terminal 50 for connection to common earth; a field supply terminal 52 for connection to the field windings of the alternator via the field terminal 26; an excitation current input terminal 54; and a sensing signal input terminal 56 for connection of an external sensing signal.

Ordinarily, the sensing signal terminal 56 of conventional, 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 connected 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 through said battery to the common junction 14, thence through battery 10 to common earth.

Means are provided for switching the output terminal 24 of the alternator to the common junction 14 upon attainment of a predetermined voltage drop across the battery 12 providing the higher voltage output, whereby to direct charging current only through the battery 10 providing the lower voltage output. This is provided by electrically actuated switch means which removably connects the output of the alternator to aid 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 alternator across only the battery 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 terminal 24 of the alternator and the common junction 14 between the batteries. The silicon controlled rectifier is normally off; hence, the switch means is normally open.

The electrical switch actuator means for turning on the silicon controlled rectifier 60 includes serially connected components viz., the voltage detecting resistors 62, 64 and 66 and the zener diode 68, the transistor 70 whose base or control electrode is connected to such components so that it is biased normally off, and the resistor 72 which connects the transistor collector or output electrode to the gate of the silicon controlled rectifier 60.

The charging control also may includes a second electrical switch actuator means for turning off the silicon controlled rectifier 60 (returning the switch means to its normally open condition). In Fig. 1 this turn-off control includes the transistor 74 which is biased normally off, the resistor 76 which interconnects the transistor collector and the sensing signal terminal 56 of the voltage regulator, and the resistors 78, 80 and 82 which, by connection across the batteries 10 and 12, form therewith a bridge network.

The operation of the charging control illustrated in Fig. 1 is as follows: With the alternator 20 being driven mechanically 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 a rising voltage at the alternator output terminal 24.

Since the silicon controlled rectifier 60 is not conducting, charging current from the output terminal cannot reach the common junction 14 directly from the alternator. Accordingly, voltage continues to rise at the output terminal until the diode 58 conducts. Thereupon charging current is conducted through the series-connected batteries 12 and 10 to common earth. 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 44, 46 and 48, zener diode 42 fires, causing the normally off transistor 32 to conduct. The normally on transistor 30 thus is turned off, causing the alternator fields to weaken and the output voltage to drop. When the voltage across the battery 10 providing the lower voltage output drops slightly, zener diode 42 ceases conduction, thereby turning off the transistor 32 and turning on transistor 30, allowing the alternator output voltage to be controlled.

When the voltage across the battery 12 providing the high voltage output reaches a predetermined value, as sensed by resistors 62, 64 and 66 zener diode 68 is caused to fire, turning on transistor 70. Activation of this transistor effects activation of the silicon controlled rectifier 60. Charging current thus is directed from the output terminal 24 of the alternator 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 and prevents the battery 12 from discharging through the silicon controlled rectifier.

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 controlled rectifier 60 to junction 14 to continue charging the battery 10 providing the lower voltage output. This occurs because, though the voltage at the base of transistor 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 therefore continues in its activated stated.

When the voltage of the output terminal 24 of the alternator drops to a predetermined value relative to the common junction 14, current stops flowing.

When the voltage across the battery 12 providing the higher voltage output drops to a lower predetermined value (the voltage across the battery 10 providing the lower voltage output remains at regulated voltage), the base of transistor 74 goes negative to a predetermined value with respect to the common junction 14, as determined by the bridge network, transistor 74 is activated. This, in turn, effects firing of zener diode 42, thereby activating transistor 32 and deactivating transistor 30. The alternator output thus is stopped, thereupon the silicon controlled rectifier 60 is deactivated.

When the voltage across the battery 10 providing the lower voltage output starts to drop, the base of transistor 74 becomes 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 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 applications, as for example, when the battery providing the higher voltage output is used only for starting an engine and charging is not needed until after a subsequent start. In such applications the silicon controlled rectifier is turned off simply by stopping the engine.

Fig. 2 illustrates a modification of the turn-off control for the silicon controlled rectifier, to accommodate the use of an original equipment voltage regulator 281, rather than incorporating a voltage regulator in the charge control, as in Fig. 1. For this purpose a transistor 84 is interposed between the collector of transistor 74 and the excitation current input terminal 54 of the voltage regulator. Thus, when the voltage across the battery 12 providing the higher voltage output drops, the base of transistor 74 goes negative with respect to the common junction 14, activating the transistor 74. This effects deactivation of transistor 84 which is biased normally on.Deactivation of transistor 84 removes power input to the regulator and effects deactivation of transistor 30, thereby stopping power to the alternator fields and deactivating the alternator and silicon controlled rectifier.

Fig. 3 illustrates a modification of the voltage regulator arrangement shown in Fig. 1. Thus, the conductor 86 interconnecting the resistors 36 and 44 in Fig. 1 is removed, and the excitation current input to the voltage regulator is provided by the conductor 88 connected between the output terminal 24 of the alternator and a separate power input terminal to the resistors 38 and 36. 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 volt age output supplies other loads in addition to engine starting. Regulator sensing across battery 10, through transistor 74, is utilized as in Fig. 1.

Fig. 4 illustrates a further modification of Fig. 1, to accommodate the use of original equipment alternators 201 which are designed for the nominal voltage of the sum of the two series-connected batteries. In this arrangement, as in Fig. 3, the conductor 86 interconnecting the resistors 36 and 44 in the voltage regulator of Fig. 1 is omitted.

However, excitation current input to the voltage regulator is supplied through conductor 90 connected directly to the higher voltage terminal of battery 12.

From the foregoing it will be appreciated that the present invention provides a charging control of simplified and therefore economical construction which functions effectively to provide precise charging of each of a pair of batteries connected together in series, and is versatile in its applicability to a wide variety of conventional charging systems.

It will be apparent to those skilled in the art that various changes may be made in the type, number, and arrangement of components described hereinbefore. For example, the control may be provided for use with positive earth systems, by substituting NPN type transistors for the PNP types illustrated, and reversing the polarities of the diodes.

The original equipment voltage regulator 381 of 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 the 12 volt batteries 10 and 12 described. For example, with battery 10 being 12 volts, battery 12 may be 6 volts to provide a total of 18 volts; 20 volts to provides a total of 32 volts; 24 volts to provide a total of 36 volts; and many other combinations. These and other changes may be made without departing from the scope of the claims.

WHAT I CLAIM IS:- 1. A charging control for use with first and second batteries serially interconnected at a common junction to provide a high voltage output at the terminal of the first battery remote from the common junction and a low voltage output at the common junction and with an electrical generator having a D.C. output to provide charging current, said charging control comprising electrically actuated switch means for transferring one pole of the D.C. output from the high voltage output terminal to the common junction, the other pole of the D.C. output remaining connected to the terminal of the second battery remote from the common junction, and electrical switch actuator means responsive to the voltage across said first battery for activating said switch means to connect the generator output across only the second battery instead of across both batteries when the voltage across said first battery reaches a predetermined value.

2. A charging control as claimed in claim 1, in which the electrically actuated switch means comprises a controlled electronic switch and is associated with a diode arranged to prevent the first battery from discharging through the electronic switch when the latter is on such diode conducting charging current to the first battery when the electronic switch is off.

3. A charging control as claimed in claim 1 or 2, in which the electrically actuated switch means is a silicon controlled rectifier.

4. A charging control as claimed in claim 1, 2 or 3 in which the switch actuator means includes serially connected components comprising a zener diode and at least one resistor such that the zener diode is fired when the voltage across the first battery reaches said predetermined value, thereby causing said switch means to be activated.

5. A charging control as claimed in claim 4 when appendant to claim 3 in which said switch actuating means includes a transistor whose control electrode is connected to said serially connected components and whose output electrode is connected to the gate of the silicon controlled rectifier.

6. A charging control as claimed in any preceding claim in which a second electrical switch actuator means responsive to the voltage across said first battery is provided for de-activating said switch means and so reapplying the generator output to both batteries when the voltage across said first battery falls to a lower predetermined value.

7. A charging control as claimed in claim 6 in which the second switch actuator means comprises a voltage divider which, in use is to be connected across both batteries, and a transistor whose control path is connected between a tapping of the voltage divider and said common junction, such that this transistor becomes conductive when the voltage across said first battery falls to said lower predetermined value and so produces a signal to deactivate the switch means.

8. A charging control as claimed in claim 6 or 7, in combination with a voltage regulator associated with said generator for controlling the excitation of the latter, the second switch actuator means being operative to override the voltage regulator and so de-excite the generator, whereby to de-activate the switch means.

9. A charging control as claimed in claim 8, in which the voltage regulator has a voltage responsive circuit with an input terminal connected to said common junction, whereby the voltage regulator regulates the voltage across the second battery.

10. A charging control as claimed in claim 9 in which the voltage responsive cir

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. battery 10, through transistor 74, is utilized as in Fig. 1. Fig. 4 illustrates a further modification of Fig. 1, to accommodate the use of original equipment alternators 201 which are designed for the nominal voltage of the sum of the two series-connected batteries. In this arrangement, as in Fig. 3, the conductor 86 interconnecting the resistors 36 and 44 in the voltage regulator of Fig. 1 is omitted. However, excitation current input to the voltage regulator is supplied through conductor 90 connected directly to the higher voltage terminal of battery 12. From the foregoing it will be appreciated that the present invention provides a charging control of simplified and therefore economical construction which functions effectively to provide precise charging of each of a pair of batteries connected together in series, and is versatile in its applicability to a wide variety of conventional charging systems. It will be apparent to those skilled in the art that various changes may be made in the type, number, and arrangement of components described hereinbefore. For example, the control may be provided for use with positive earth systems, by substituting NPN type transistors for the PNP types illustrated, and reversing the polarities of the diodes. The original equipment voltage regulator 381 of 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 the 12 volt batteries 10 and 12 described. For example, with battery 10 being 12 volts, battery 12 may be 6 volts to provide a total of 18 volts; 20 volts to provides a total of 32 volts; 24 volts to provide a total of 36 volts; and many other combinations. These and other changes may be made without departing from the scope of the claims. WHAT I CLAIM IS:-

1. A charging control for use with first and second batteries serially interconnected at a common junction to provide a high voltage output at the terminal of the first battery remote from the common junction and a low voltage output at the common junction and with an electrical generator having a D.C. output to provide charging current, said charging control comprising electrically actuated switch means for transferring one pole of the D.C. output from the high voltage output terminal to the common junction, the other pole of the D.C. output remaining connected to the terminal of the second battery remote from the common junction, and electrical switch actuator means responsive to the voltage across said first battery for activating said switch means to connect the generator output across only the second battery instead of across both batteries when the voltage across said first battery reaches a predetermined value.

cuit has a second input terminal connected to said second switch actuator means, such that an input to said second regulator input terminal responsive to the voltage across said first battery falling to said lower predetermined value overrides the voltage input to said first regulator input terminal.

11. A charging control as claimed in claim 10 in which the voltage responsive circuit comprises a series arrangement of a zener diode and at least one resistor, such that the zener diode is fired to switch off the excitation current when the second switch actuator means responds to said lower predetermined value.

12. A charging control as claimed in claim 9 in which said regulator input terminal is connected via a normally conducting transistor switch to said common junction and said second switch actuators means is arranged to turn such transistor off responsively to the voltage across said first battery falling to said lower predetermined value.

13. A charging control as claimed in claim 9, 10, 11 or 12 in which the said regulator input terminal serves also as an excitation current input terminal for the regulator.

14. A charging control as claimed in claim 9, 10 or 11 in which the voltage regulator has a separate excitation current input terminal which is connectible to the generator output or to the high voltage battery output terminal.

15. A charging control constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

16. A charging control as claimed in claim 15 but modified substantially as herein described with reference to and as illustrated in Fig. 2 of the accompanying drawings.

17. A charging control as claimed in claim 15 but modified substantially as herein described with reference to and as illustrated in Fig. 3 of the accompanying drawings.

18. A charging control as claimed in claim 15 but modified substantially as herein described with reference to and as illustrated in Figure 4 of the accompanying drawings.~