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How to charge NiMH batteries

Old 03-17-2013, 07:29 AM
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JPMacG
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Default RE: How to charge NiMH batteries

I have a thought regarding NiMH and C/10 charging.... C/10 for a typical AA sized NiMH cell is 200 to 300 mA. However C/10 for a typical NiCd cell is only about 70 mA.

Suppose you use a timed C/10 charge. Of course you never know exactly when stop the charge, so you charge for more than enough time, e.g. 14 hours. Once the cell is fully charged the power from the charger is turned into heat and dissipated within the cell.

There is a big difference between dissipating charge power at 70 mA and at 200 mA. But the physical size of the NiMH and NiCd cells are the same. So the NiMH cell during overcharge will get warmer than the NiCd cell during overcharge.

Maybe this is why NiMH cells don't tolerate C/10 charge well. Maybe we should charge at 70 mA for 40 hours (or whatever). Maybe the charge rate for a timed charge should be determined by the physical cell size and not the cell capacity.

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