Method and apparatus for charging sealed Ni-Cad batteries

• US 4,213,081 A
• Filed: 02/27/1978
• Issued: 07/15/1980
• Est. Priority Date: 02/27/1978
• Status: Expired due to Term

• Current Assignee: Earnest R. Taylor
• Original Assignee: Earnest R. Taylor
• Inventors: Taylor, Earnest R.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/881,179
• Time in Patent Office: 869 Days
• Field of Search: 320/39, 320/40, 320/2, 320/DIG. 1, 328/132
• US Class Current: 320/148
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient

Abstract

A sealed nickel-cadmium battery having a voltage-charge characteristic with a single peak voltage value that is in the overcharge region is charged by applying a charging current to the battery while monitoring the battery terminal voltage, and terminating or substantially reducing the charging current when the battery terminal voltage reaches the peak value. Specifically, to determine when the terminal voltage of the battery reaches the peak value, the maximum value attained by the battery terminal voltage is stored on an ongoing basis while applying the charging current, and the stored maximum value is compared with the instantaneous value of the battery terminal voltage. When the stored value exceeds the instantaneous value, the peak value is indicated.

Claims

1. An electrical energy storage system comprising:

a sealed nickel-cadmium battery having first and second terminals;

a source of charging current;

disconnectable means for applying a large charging current from the source to the battery;

a diode and a capacitor connected in series between the first and second terminals of the battery, the diode being connected to the first terminal and the capacitor being connected to the second terminal to form therebetween a junction, the diode being poled to charge the capacitor as the battery voltage increases;

comparing means having first and second inputs;

means for connecting the junction to the first input of the comparing means;

a connection from the first terminal of the battery to the second input of the comparing means including means for compensating for the voltage drop across the diode; and

means responsive to the comparing means for disconnecting the applying means when the voltage at the second input drops below the voltage at the first input.

2. The system of claim 1, additionally comprising connectable means for applying a small sustaining charging current from the source to the battery, and means responsive to the comparing means for connecting the small current applying means when the large current applying means is disconnected.

3. The system of claim 1, additionally comprising a normally open manually operated discharge switch connected across the capacitor.

4. The system of claim 1, in which the second input of the comparator is set higher than the first input of the comparator.

5. The system of claim 1, in which the compensating means comprises a potentiometer.

6. Charging apparatus for a sealed nickel-cadmium battery having a terminal voltage comprising:

a source of charging current;

disconnectable means for applying a large charging current from the source to the battery;

means for storing the maximum value attained by the battery terminal voltage on an ongoing basis, the storing means comprising a pulsed oscillator, means for counting the oscillations of the oscillator, means for converting the counted oscillations to an analog signal, and means for actuating the oscillator as long as the analog signal is less than the battery terminal voltge to cause the counted oscillations to follow the maximum value of the terminal voltage of the battery;

means for comparing the stored maximum value with the instantaneous value of the terminal voltage, the comparing means comprising a comparator having a first input to which the analog signal is applied and a second input to which the battery terminal voltage is applied; and

means responsive to the comparing means for disconnecting the applying means when the instantaneous value of the terminal voltage is less than the stored maximum value of the terminal voltage.

7. The system of claim 6, in which the counting means comprises a resettable binary counter, the system additionally comprising means for periodically resetting the counter.

8. An electrical energy storage system comprising:

a sealed nickel-cadmium battery having first and second terminals;

a source of charging voltage;

a transistor having a collector connected to the source of charging voltage, an emitter connected to the first terminal of the battery, and a base;

a diode and a capacitor connected in series between the first and second terminals of the battery, the diode being connected to one terminal and the capacitor being connected to the other terminal to form a junction therebetween, the diode being poled to charge the capacitor when the battery voltage is increasing;

a comparator having first and second inputs and an output connected to the base of the transistor, the output of the comparator causing the transistor to cut off when the voltage applied to the second input drops below the voltage applied to the first input;

means for connecting the junction to the first input; and

means for connecting the one terminal of the battery to the second input.

9. The system of claim 8, in which the means for connecting the one terminal of the battery to the second input comprises a potentiometer set to compensate for the voltage drop across the diode.