Building an 8.4v Ni-Mh Charger

crgwbr

Hey Everyone,
I have·3 8.4v Ni-Mh battery packs (2500 mAh "AA" size) that I need to charge.· I would like to build a charger that will do all 3 at the same time, about 400-500 mA each.· Does anyone have a schmatic for something like this?· If not, how about just the general theory of how a charger like this would work?

Thanks,
crgwbr

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NerdMaster
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Unsoundcode

Hi crgwbr, this link actually mentions charging NiMH 8.4v .

http://www.electronics-lab.com/projects/power/037/index.html

Jeff T.

LoopyByteloose

The only problem with series charging of Ni-Mh is if one cell suffers a reverse polarity. It will certainly die. I suspect that is why the commercial chargers are in parallel with fool proof connections. Ni-Mh and Ni-Cd are more sensitive to this mishandling than other batteries.

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crgwbr

These batteries will be in Shrinkrapped Packs, With connecters that will only plug in on way, I'd call that fool proof.

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Tom Walker

crgwbr,
I think what Kramer was referring to is the "ability" of a Ni-Mh cell to spontaneously change polarity when fairly deeply discharged. This behavior is due to the electrochemical make-up of the cell and is well-documented. It is not overly common, but when it happens, it can cause "interesting" (and sometimes difficult to diagnose) displays/problems. Imagine if one of the "middle" cells in your pack just decided to act like it was reversed...

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Truly Understand the Fundamentals and the Path will be so much easier...

crgwbr

Wow, I didn't know they could do that. I guess I could just make sure I don't discharge them very deeply.

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NerdMaster
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