Electronic control system for battery chargers

• US 3,886,428 A
• Filed: 05/14/1974
• Issued: 05/27/1975
• Est. Priority Date: 05/17/1973
• 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:
  US05/469,763
• Time in Patent Office: 378 Days
• Field of Search: 320/20,39,40,48,30
• US Class Current: 320/156
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: Y10S 320/17 Sensing of "gassing" voltage

Abstract

An electronic control system for battery chargers in which the charging current is switched on and off at predetermined intervals of time, and the magnitude of the charging current during the ON periods is controlled from a signal produced from the electronic control system. On switching OFF the charging current at each cycle of operation, the rate of decay of battery voltage is utilized to form a control signal, having first removed the voltage drop on switch off due to the ohmic resistance of the battery, known as the '"'"''"'"''"'"''"'"'I.R Drop.'"'"''"'"''"'"''"'"' Having extracted the '"'"''"'"''"'"''"'"'I.R Drop,'"'"''"'"''"'"''"'"' the remaining rate in decay in voltage representing the '"'"''"'"''"'"''"'"'Gas Drop'"'"''"'"''"'"''"'"' due to potential changes in the layer of gas on the active surfaces of the electrode, is compared with a standard reference voltage, the result of said comparison being utilized to vary the magnitude of the charging current in accordance with the state of charge of the battery as determined by the rate of decay of battery terminal voltage, due to the '"'"''"'"''"'"''"'"'Gas Drop.

Claims

1. An electronic control system for a battery charger including:

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;

means for providing a signal for controlling the magnitude of the 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 which is some function of the differential at the repetitive intervals;

means for comparing this voltage derived from the differential with a standard voltage; and

means utilizing the difference between said two voltages in order to modify the control signal whereby the magnitude of the charging current is controlled.

2. An electronic control system according to claim 1, wherein the means for switching on and off the charging current is an electronic timer comprising:

an operational amplifier;

feedback means for causing said amplifier to switch on and off in a predetermined cycle;

means for adjusting the ON/OFF ratio of the amplifier as well as the length of the cycle; and

means for blocking the passage of the control signal from the control system in the absence of an output of the amplifier, whereby the charging current is cut off when the operational amplifier is OFF.

3. An electronic control system according to claim 1, wherein the means for extracting the resultant '"'"''"'"''"'"''"'"'I.R Drop'"'"''"'"''"'"''"'"' comprises a transistor, and a differentiating circuit connected to the base electrode of said transistor for rendering said transistor temporarily conductive on application of a pulse to the differentiating circuit from the means for switching on and off the charging current, said transistor effectively shorting-out said means for differentiating the rate of decay of the terminal voltage during the time that it is rendered conductive.

4. An electronic control system according to claim 3, wherein the means for differentiating the rate of decay of the terminal voltage comprises a resistor and a capacitor, said resistor being connected in parallel with the collector-emitter path of said transistor, said capacitor being connected between one end of the resistor and one terminal of the battery to be charged.

5. An electronic control system according to claim 1, wherein the means for deriving a voltage which is some function of the differentiated rate of decay of the terminal voltage comprises:

a capacitor, the capacitor being charged in each OFF part of the repetitive charging cycle from the means for differentiating the rate of decay of the terminal voltage after the '"'"''"'"''"'"''"'"'I.R Drop'"'"''"'"''"'"''"'"' has been extracted; and

means for discharging the capacitor at the commencement of each OFF period of the charging cycle, the capacitor acting as a memory in storing a voltage proportional to the peak of the differentiated rate of decay of battery terminal voltage.

6. An electronic control system according to claim 5, wherein the means for discharging the capacitor comprises:

a transistor whose collector-emitter path is in parallel with the capacitor and a differentiating network connected to the base electrode of the transistor;

said means for switching on and off the charging current producing a negative going signal at switch off, said signal after differentiation causing the transistor to momentarily conduct and discharge the capacitor.

7. An electronic control system according to claim 1, wherein the means for comparing the derived voltage which is some function of the differential with a standard voltage comprises a differential amplifier consisting of first and second transistors, the emitter-collector path of said transistors being common on one side thereof, the first transistor receiving on its base electrode the derived voltage which is proportional to the differential whilst the second transistor receives on its base electrode a standard reference voltage.

8. An electronic control system according to claim 7, wherein the standard reference voltage is generated from a zener diode and potentiometer in parallel with one another and with the collector-emitter paths of said transistors, a tap of the potentiometer being connected to the base electrode of the second transistor.

9. An electronic control system according to claim 7, wherein an integrator, in the form of a series circuit comprising a resistor and capacitor, is associated with the uncommon collector-emitter circuit of the second transistor, the control signal being generated by said integrator as a result of the comparison between the derived voltage and the standard voltage.

10. An electronic control system according to claim 1, comprising:

a filter for filtering out the rectified A.C. component of the voltage across the terminals of the battery to be charged;

a capacitor-resistor differentiator for extracting the '"'"''"'"''"'"''"'"'I.R Drop'"'"''"'"''"'"''"'"' and differentiating the rate of decay of the terminal voltage across the battery during the OFF periods;

a peak memory for storing at each repetitive cycle the peak value of the differentiated decay of terminal voltage;

a standard voltage;

a comparator for comparing the value of the peak voltage stored in the peak memory during each OFF period with the value of the standard voltage;

an integrator operable from the results of said comparison in order to modify the control signal whereby the magnitude of the charging current is controlled; and

a timer for switching ON and OFF said control signal and the charging current to the battery at repetitive intervals.

11. An electronic control system according to claim 10, additionally including:

a second capacitor-resistor differentiator arranged in parallel with the first capacitor differentiator, said second capacitor-resistor being arranged in parallel with the first differentiator and having no means for extracting the '"'"''"'"''"'"''"'"'I.R Drop'"'"''"'"''"'"''"'"' so that the differentiated output includes the '"'"''"'"''"'"''"'"'I.R Drop;

'"'"''"'"''"'"''"'"' and an AND gate arranged between the comparator and integrator for receiving the output from the comparator and the second capacitor-resistor differentiator on a pair of inputs.

12. An electronic control system according to claim 10, additionally including:

an AND gate arranged between the comparator and the integrator for receiving the output from the comparator and from the capacitor-resistor differentiator on a pair of terminals.

13. An electronic control system according to claim 1, wherein the means for comparing the derived voltage which is the peak value of the differential with a standard voltage is an operational amplifier having a pair of inputs, the peak value of the differential which has been stored in a capacitor being applied to the first input of the operational amplifier, whilst a standard voltage derived across a parallel circuit comprising a zener diode and a potentiometer being applied to the second input from the tap of the potentiometer.

14. An electronic control system according to claim 1, wherein means are provided for tapping off a sample from the battery terminal voltage, in the case where the battery to be charged has a large number of cells, whereby said electronic control system is adapted to charge any battery irrespective of the number of cells and its capacity.

15. An electronic control system according to claim 14, comprising:

a series circuit across the battery terminals including, a first transistor, a zener diode and a capacitor;

a resistor; and

a second transistor whose base electrode is connected to the junction between the zener diode and the capacitor and whose collector-emitter path is in series with said resistor across said series circuit, the junction between the second transistor and resistor being connected to the base electrode of the first transistor, and also to the means for extracting the '"'"''"'"''"'"''"'"'I.R Drop.'"'"''"'"''"'"''"'"'

16. An electronic control system according to claim 14, comprising first and second transistors;

a zener diode, first and second resistors; and

a capacitor;

sAid first resistor and zener diode being connected in series across the battery terminal voltage, the base electrode of the first transistor being connected to the junction between the first resistor and zener diode, the collector-emitter circuits of the two transistors being in parallel with one another, but in series with the second resistor across the battery terminal voltage, the first transistor also being in series with the capacitor, the base electrode of the second transistor being connected to the junction between the capacitor and collector-emitter path of the first transistor, the junction between the second resistor and the paralleled collector-emitter paths of the two transistors being connected to the means for extracting the '"'"''"'"''"'"''"'"'I.R Drop.'"'"''"'"''"'"''"'"'