Simple NICAD Charging Jonny Klein K7JK copyright 1991 Jonathan D. Klein Like Jeff Damm (Build a Constant Current Source, Home Power #21, page 82) I've been charging NICADS with a constant current source for many years. But being very lazy I didn't spend many hours tinkering. I just used an LM317 in the data book constant current configuration: INSERT DIAGRAM Since a regular old LM317 in the K or T package can source at least 1.5 Amps it can charge most NICADS at the C/10 rate with no trouble. I have a cheap digital multimeter I put in series as an ammeter to adjust the resistor, and I put the whole gadget on a timer. I set the current for C/10 and the timer for 15 hours and let er' rip. To keep your batteries at their greatest capacity, discharge them to about 1.20 volts before charging. Don't forget a series diode so the batteries won't discharge through the circuit when the timer kicks off. You can use this circuit for any number of batteries of the same capacity so long as the voltage of your power supply is great enough; and it will work equally well from your car's battery with the same stipulation. I've been charging my batteries this way for many years with excellent results - some of my batteries are up to 7 years old and still have full capacity even though I got some of them used. I have several different battery packs with different numbers of batteries - this constant current charger does fine regardless of the number of cells in the pack if the current is set right. In fact you can even charge two packs at the same time (in series of course) if you have enough supply voltage. But make sure you don't exceed the maximum voltage drop of 40 volts across the LM317. Also make sure that the pass resistor is heavy duty enough to carry the current and dissipate the power (= I2R)NOTE SUPERSCRIPT. I got some heavy duty pots from Hosfeldt or Fair Radio Sales, I don't remember which. One final note on NICADS - I've cycled several different cells and find that you get about 25% capacity dropping to 1.28 volts. It will stay very close to 1.28 volts for another 50% of the capacity; then drop to about 1.20 volts when you use the last 25%. Access Jonathan D. Klein K7JK, Talsalsan Farm, 12330 Takilma Rd., Cave Junction, OR 97523.