Control systems for battery chargers

• US 3,987,353 A
• Filed: 11/20/1974
• Issued: 10/19/1976
• Est. Priority Date: 12/21/1973
• Status: Expired due to Term

• Current Assignee: James Adrian Macharg
• Original Assignee: James Adrian Macharg
• Inventors: Macharg, James Adrian
• Primary Examiner(s): Miller, J D
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/525,551
• Time in Patent Office: 699 Days
• Field of Search: 320/21-24, 320/39, 320/40, 320/48, 320/46
• US Class Current: 320/161
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: Y10S 320/17 Sensing of "gassing" voltage

Abstract

A battery charger control system in which the charging current is switched on and off at repetitive intervals, the open circuit terminal voltage during the "off" periods being utilized to provide a control signal in order to vary the magnitude of the charging current during the "on" periods. The control signal is derived by extracting the resultant "I.R. Drop" at the battery terminals once the charging current has been switched off and then differentiating the rate of decay of the open-circuit terminal voltage of the battery. A voltage is then derived from the differential and used in one of three ways to control the magnitude of the charging current in order to progressively reduce its magnitude once gas generation has been detected as a result of a significant differential occuring.

Claims

1. A control system for a battery charger including:

means for switching on and off the charging current at repetitive intervals in order to provide a open circuit terminal voltage during the off periods;

means for providing a signal for controlling the magnitude of the charging current;

means for varying said signal between a maximum to provide maximum charging current and a minimum to provide minimum charging current;

means for extracting the resultant I.R. Drop at the battery terminals;

means for differentiating the rate of decay of the open-circuit terminal voltage of the battery at the said repetitive intervals;

means for deriving a voltage from said differential during the repetitive intervals, said voltage being a function of gas generation;

means for utilizing said voltage derived from the differential to cause said control signal varying means to vary said control signal in order to progressively reduce the magnitude of the charging current once gas generation has commenced.

2. A control system according to claim 1, wherein the voltage derived from the differential is stored with decay, this function being used to control the means for varying said control signal in order to bring about a reduction in charging current once gas generation has been detected.

3. A control system according to claim 1, further comprising an electronic gate, wherein the voltage derived from the differential is stored and utilized to control the electronic gate, the means for switching on and off the charging current also controlling the electronic gate whereby if gas generation has been detected the electronic gate controls the means for varying the control signal in order to bring about a reduction in charging current.

4. A control system according to claim 1, including means for storing the voltage derived from the differential, means for detecting a rise of the differential in the next cycle, means for storing the detected rise, and means for preventing the charging current being reduced as a result of a detected differential due to Gas Drop until the peak differential has been reached.

5. A control system according to claim 1, wherein the means for switching on and off the charging current at repetitive intervals in order to provide an open circuit terminal voltage during the off periods includes:

a timer providing positive and negative going outputs at a predetermined frequency and mark space ratio; and

a gate for passing the control signal to a charging current control stage when unblocked, the gate being controlled by the output of the timer stage.

6. A control system according to claim 1, wherein the means for providing a control signal includes:

a control voltage output stage;

a capacitor; and

a discharge stage for partially discharging the capacitor from a limit value in each cycle of repetitive on/off intervals thereby forming in the control voltage output stage the desired control signal said discharge stage being controlled to effect the partial discharge of the capacitor by the voltage which is derived from the differential.

7. A control system according to claim 1, wherein the battery terminal voltage is differentiated by means of a capacitor and resistor in series.

8. A control system according to claim 7, wherein the means for extracting the resultant I.R. Drop every time the charging current is switched off includes a transistor, the collector-emitter path of the transistor being connected in shunt with the resistor of the differentiating circuit, and means for applying a biasing pulse to the base electrode of said transistor to cause it to short circuit the resistor every time the charging current is switched off whereby the I.R. Drop across the capacitor is extracted.

9. A control system according to claim 8, wherein the means for switching on and off the charging current at repetitive intervals in order to provide an open circuit terminal voltage during the off periods includes a timer providing positive and negative going outputs at a predetermined frequency and mark space ratio, said output from the timer being connected to the base electrode of the transistor through a capacitor and resistor circuit acting as a differentiator to provide a biasing pulse to cause said transistor to conduct every time the timer switches off the charging current.

10. A control system according to claim 2, wherein the means for deriving said voltage from the differential includes:

a comparator;

a limiter stage; and

a store, connected in cascade between the means for differentiating the rate of decay of said open circuit terminal voltage and the means for utilizing said derived voltage to vary the control signal.

11. A control system according to claim 3, wherein the means for deriving said voltage from the differential includes:

a peak memory circuit;

an AND gate constituting the electronic gate; and

a canceller circuit associated with the peak memory circuit for cancelling the peak voltage remembered in the peak memory circuit during each cycle, said AND gate providing an output to said control voltage varying means.

12. A control system according to claim 11, wherein the canceller circuit is operated from a second output of the AND gate.

13. A control system according to claim 11, wherein the canceller circuit is operated from an output of the means for initiating the switching on and off of the charging current at repetitive intervals.

14. A control system according to claim 4, wherein the means for deriving said voltage from the differential includes:

a peak memory circuit;

a rise detector and memory circuit;

a NAND gate; and

first and second canceller circuits, the NAND gate receiving on a first input, the output from the rise detector and memory circuit and on a second input a signal from the means for initiating the switching on and off of the charging current at the repetitive intervals, the NAND gate providing on a first output a signal for said control voltage varying means and on a second output a signal to the first canceller circuit;

the first and second canceller circuits being associated with the peak memory circuit and rise detector memory circuit respectively, the second canceller circuit receiving a signal from the means for initiating the switching on and off of the charging current.

15. A control system according to claim 2, wherein the control signal varying means includes a capacitor, a control voltage output stage, and discharge stage for discharging said capacitor in steps, said capacitor when fully charged maintaining, through the control voltage stage, the charging current at a maximum during the on periods, said capacitor discharge stage effecting a discharge of the capacitor in steps once the voltage derived from the differential exceeds a given value.

16. A control system according to claim 15, wherein said capacitor discharge stage includes a transistor and a string of series connected diodes, the emitter-collector path of the transistor being in series with the string of diodes across said capacitor, the derived voltage being applied to the base electrode of said transistor at cyclic intervals corresponding to the repetitive on/off intervals of the charging current in order to cause conduction of the transistor during said decay and hence partial discharge of the capacitor in steps at the repetitive intervals, means being provided for preventing the discharge of the capacitor until the derived voltage has exceeded a given value.

17. A control system according to claim 16, wherein said decay is caused by the provision of a parallel circuit comprising a second capacitor and resistor, means for amplifying the derived voltage, and means for limiting said amplified signal in height before applying it across the second capacitor such that the second capacitor is charged to a fixed level every time a significant differential is present.

18. A control system according to claim 17, wherein said voltage limiting means is a zener diode.

19. A control system according to claim 17, additionally including a transistor which amplifies the excess of the derived voltage applied across its base-collector electrodes.

20. A control system according to claim 16, wherein the means preventing the discharge of the capacitor until the derived voltage has exceeded a given value comprises a bistable circuit, said bistable circuit in one of its states being operative to prevent discharge of the capacitor, said bistable receiving on a first input a negative going pulse, and receiving on a second input a positive going pulse derived from the differential when the derived voltage exceeds a given value;

said latter pulse effecting a change of state of the bistable circuit to render it inoperative and thus allowing the capacitor to be discharged in steps at the repetitive intervals.

21. A control system according to claim 15, wherein the control voltage output stage includes a field-effect-transistor and a pair of transistors connected with their emitter-collector paths in series with one another and with a resistor, the control signal being derived across said resistor, the base electrode of one transistor receiving a signal from a timer means in order to effect the switching on and off of the charging current at said repetitive intervals, the base electrode of the second transistor receiving a signal from the field-effect-transistor representative of the amount by which the capacitor has been discharged in order to proportionally reduce the current flow through the pair of transistors and hence said resistor so as to reduce the control signal for the charging current.

22. A control system according to claim 14, wherein the peak memory circuit comprises a capacitor, diode and resistor in series with one another and in series with the emitter collector path of a transistor whose base electrode receives the derived voltage from the differential, a rise beyond the previous peak being detected due to the fact that the capacitor must be further charged in each cycle of on/off operation.

23. A control system according to claim 22, wherein the first canceller circuit comprises a transistor whose collector-emitter path is connected across the capacitor, the base electrode receiving a signal from the NAND gate to cause the conduction of the transistor and hence discharge the capacitor once complete polarization has been detected.

24. A control system according to claim 14, wherein the rise detector and memory circuit include a pair of transistors, a diode and a capacitor, the transistors amplifying and voltage in excess of the peak detected at the previous cycle, the capacitor storing the detected rise.

25. A control system according to claim 24, wherein the second canceller circuit comprises a transistor whose collector-emitter path is connected across the capacitor, the base electrode receiving a pulse from a timer circuit controlling the switching on and off of the charging current in every cycle of operation.

26. A control system according to claim 15, wherein said capacitor discharge stage includes a transistor and a potentiometer whose tap is connected to the collector-emitter path of the transistor, so that at least one part of the potentiometer is in series with the collector-emitter path of the transistor across the capacitor, a zener diode being connected across the extremities of the potentiometer, the derived voltage being applied to the base electrode of said transistor at cyclic intervals according to the repetitive on/off intervals of the charging current in order to cause conduction of the transistor during said decay and hence partial discharge of the capacitor in steps at repetitive intervals, the minimum voltage to which the capacitor can be discharged being determined by the position of the tap on the potentiometer.