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NiMH; what temperature for recharging?

Discussion in 'Hobby Electronics' started by Terryc, Apr 4, 2008.

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  1. Terryc

    Terryc Guest

    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.
     
  2. 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.
     
  3. Terryc

    Terryc Guest

    John Tserkezis wrote:

    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.
    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.
     
  4. Pete

    Pete Guest

    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
     
  5. Alan Peake

    Alan Peake Guest

    Have a look at:

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

    For some details of charging NiMH Batteries.

    Alan
     
  6. Jason James

    Jason James Guest

    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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