Make a Constant Current Nicad Charger
by Pete Christensen
Parts List
o Bridge Rectifier or four 1N4001 diodes
o Transformer, 117V/30V & 500mA
o D1/D2 (near 'b' of transistor), 1N4001
o Transistor, 2N3055
o Resistor, 2.7K
o Capacitor, 470 to 680 microFarad
o Adjustable potmeter, 20 to 25 ohms
o Meter, 0 to 200 mA (or use your multimeter)
The schematic for this charger is pretty simple. You can charge from 1 to 20 +/- nicads at a constant current of from 20 to 200 ma +/-. The circuit I modified from an article in July 1977 "73 Amateur Radio Magazine". The transformer can be anything from 24 volts (lower volts=fewer cells charged) up to 30 or so volts. The more volts the more cells you can charge. All diodes are 1N4001 or similar. The cap can be most anything around 500uf or greater. The meter can be any ammeter if you wind your own shunt. I've built and used 2 or them for years. Good luck!
Pete Christensen
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