Nicad Battery Charger

This simple charger uses a single transistor as a constant current source. The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base - emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. The charging current is approximately 15mA or 45mA with the
Nicad Battery Charger - schematic

switch closed. This suits most 1. 5V and 9V rechargeable batteries. The transformer should have a secondary rating of 12V ac at 0. 5amp, the primary should be 220/240volts for Europe or 120volts ac for North America. WARNING: Take care with this circuit. Use a voltmeter to observe correct polarity. Nicads can explode if short circuited or connected with the wrong polarity.

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