How To Charge 1.2v Battery?

I picked up two 1/3 AA, 1.2v, Ni-Cd, 150mAh. Got them for C$2.95 each at a local store (that's the only capacity they carry).

However, how do I charge them? Do I set my charger to 1.2v and once that it reach 1.2v, it'll stop charging them? or do I set it to 1.3v? My charger consist of an AC to DC 1.5v and I'll add in a few resistors to drop the voltage down to 1.2v or 1.3v.

Howdy CalgaryGuy,

NiCds are most easily charged by constant current. The general 'slow charge' formula is 1/10 the capacity (in your case 15 mA, for 12 to 14 hours. NiCds can take moderate over charging without ill effect (unlike NiMH), so time isn't all that important.

In practice, how about say 470 or 510 ohms in series with your cell and setting your supply to 7.5 Volts across the resistor (for 15 mA) plus 1.3 or so for a total of 8.8 Volts. I used to do this 'overnight', that is start it at 6 or 8 in the evening, take it off in the morning. I also used to set them us 'a little light' (just under 1/10) at work when I left, and collect them first thing in the morning.

Doug Owen

Hm... Not sure if I can archive that, mine is a cheap $10 charger which I plug it into the wall and it has a switch from 1.5v, 3.0v, 4.5v... to 12.0v. I was going to just leave it at 1.5v with a resister to lower it to 1.2v.

Other than that, I also have a cheap solar charger which can charge 1.2v AA Ni-Cd battery.

No problem, go to 750 ohms, half watt or more, and use the 12 Volt setting. Don't worry about the voltage (it's just the pressure) we're trying for constant current (flow rate) here. Just charge the dead ones for 12 to 14 hours and take them off no matter what their voltage is.

FWIW, you can charge both of them in series with the same current (cell, cell, resistor, source). Or use a second resistor, your call.

Doug Owen

Actually, I did some calculations, I'm better off using the solar charger. I can get full charge on a cloudy day in about 12 hours. Thanks for replying to my post and gave me ideas on how to buid my own future charger.

You're welcome.

Based on my own modest experiences with such chargers, I'd want to test it a bit before I'd 'take it to the bank in Denver'. Stated performance might be termed 'optimistic'...

Good luck.

Doug Owen

The solar charger that I bough came with two AA, Ni-Cd, 1.2v, 850mAh. I already tested those and it take about a week to charge it so about one day should be good for me to charge two 1/3 AA, 150mAh.