/diy/ - Do It Yourself

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Bojangles Wed Jan 30 14:09:38 2013 No.386026 [Reply] [Original]

hey /diy/. I'm pretty new to electronics and don't understand half of what google shows me, so i was wondering if you guys could help me. I've got the pictured battery, a use for it, but no way to charge it. i already figured out that I'd need 10mA of current going into it, but I've got no idea what voltage to use or which end to connect to +/- from the power supply when charging.

tl;dr - help me charge a 150mAh 2/3 AA?

>>	Bojangles Wed Jan 30 14:10:22 2013 No.386028 correction - 15mA to charge. I'm very sleep deprived right now.

>>	Anonymous Wed Jan 30 14:24:52 2013 No.386034 A 1V DC supply or wall-wart. positive to positive, negative to negative.

>>	Bojangles Wed Jan 30 14:27:06 2013 No.386039 >>386034 thanks.

>>	Anonymous Wed Jan 30 15:36:37 2013 No.386075 >>386039 AA, AAA, C, D, all those not nine volt batteries are 1.5 V. There are also some that are 3V and 6.3V, for sporting goods and shit. Lithium Ion is 3.6 (Ideally, I think), but 3V in reality.

>>	Anonymous Wed Jan 30 15:39:52 2013 No.386079 >>386075 It's still usually around 3.7 unless you buy it from eBay.

>>	Anonymous Wed Jan 30 15:46:07 2013 No.386084 >>386075 >>386079 OP's battery says Ni-Cd and 1.2V. Maximum voltage is around 1.4V. They're usually charged with constant current charger, like OP said.

>>	Bojangles Thu Jan 31 00:39:28 2013 No.386439 >>386075 >>386084 but the output from the charger to the 1.2v or 1.5v cell would be 1v?

>>	Anonymous Thu Jan 31 00:41:59 2013 No.386442 >>386439 Aren't trickle charges usually over the nominal voltage? And NiCd are usually charged at 1xCapacity right?

Anonymous Thu Jan 31 01:25:14 2013 No.386477

Polarity for charging is the same as for discharging. You're already reversing the flow of current by using the battery as a load instead of a source, no need to physically reverse the battery.

A proper charging profile for NiCd is 1.4V constant current at 1/10 C until termination.

Termination being when cell open circuit voltage reaches 1.4V.

That said, NiCd is highly robust. It can withstand up to 1C rate of charge, and there's a bit of leeway in voltage tolerance.

anus presley Thu Jan 31 01:35:44 2013 No.386483

> Aren't trickle charges usually over the nominal voltage?

yes, if you want current flowing into the battery instead of out it.

>And NiCd are usually charged at 1xCapacity right?

no, they would get too hot and die sooner. you want 10% of capacity (15mA) for a 10-hour charge, and around 50mA for a 3-hour charge.

the answer to OPs question is this: DC wall-wart rated at least 100mA, somewhere around 4-12 volts, and a series resistor. The resistor is calculated as such:
- assuming a 6V wall-wart, and a 15mA, or 10-hour, charge: (6 - 1.2) / 0.015 = 320 ohms.
- the power capacity of the resistor is current squared times resistance = .015 * .015 * 320 = .072 W

So a small quarter-watt resistor is fine. Radio Shack model 271-1315.

>>	neckbeard_the_pirate Thu Jan 31 01:44:28 2013 No.386490 >>386026 Just giving a friendly bump for this guy >>386483

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