Ni-Cad (NiCd, NiCad) battery, sometimes doesn’t work as expected, gives no power and cannot be recharged. In this situation, the battery need to be reconditioned. It’ is possible that the battery is internally shorted, and we can get the battery into life again by recondition the Ni-Cad battery using a zapper circuit. This circuit restore the Ni-Cad battery from shorting by forcing a high current flow to burn the internal dirt. The current stored in the high capacitance capacitor is heavy discharged by the SCR when zapping, and the SCR is used to disconnect the battery connection when charging the capacitor. A 120 ohm 10W resistor is used to limit the current when charging the capacitor, and you have to make sure the LED’s intensity has reach the steady state before switching to zap position. After zapping the battery and switch to charge position, the charging process will take some period and indicated by the LED which will gradually increase the brightness until get stable intensity when fully charged. The power supply for this circuit can be taken from small transformer (350 mA to 1 A) with half or full wave rectifier. Here is the schematic diagram of the battery zapper circuit:

 

Ni Cad Battery Zapper circuit schematic