NiMH; what temperature for recharging?

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What temperature should NiMh batteries get up to when being recharged?


Have four Sony brand AA being recharged in the Sony brand recharger they
came with. They feel very hot to me.

Might be time to claim a warranty swap.

Re: NiMH; what temperature for recharging?

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  Depends on how much current it's pushing into them.  At medium/low currents,
it's generally considered charged when cell temperature rises 5C above
starting ambient.
  However, at fast charge rates, it's "normal" for them to heat up past that
anyway.  My charger heats some AAs to fairly warm.  Wouldn't quite say hot
though.  I've read some reports (with my charger) that with some batteries,
they can get quite hot at completion of charge, so expect that to be 'normal'.

  I'd also hazzard a guess and say if you do warranty swap, you'll see the
exact same thing happen again.
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Re: NiMH; what temperature for recharging?

Thanks. Helpful. It was normally 24hours to charge up the AA. Trouble is
I have no idea of the actual capacity (~700 digitial images in the
camera is the only clue), so I have no idea if that is fast or slow.

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Well, at least I'll have lights then. After I posted, the led went out
(orange for charging, green for charged), so I'd say the unit is cactus.

Re: NiMH; what temperature for recharging?

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Most chargers with maximum temperature cutoff are set to around 45C.

However, how hot the batteries get during charging is a function of how
much current you're putting into them - for example, with a typical
overnight trickle charge (0.1C), I wouldn't expect the batteries to get
noticeably warm at all, while with a 15 minute fast charger, I'd expect
them to almost get too hot to touch.

Peter

Re: NiMH; what temperature for recharging?


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Have a look at:

   http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

For some details of charging NiMH Batteries.

Alan


Re: NiMH; what temperature for recharging?

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It's normal if they are "fast" charge. The Varta 15 minute, AA NiMH charger
elevates the 2 AAs temperatures to bordering on hot. Its one of the best
rechargeable battery setups I've used.

Jason



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