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NiCad vs. NiMH Battery Chargers

Discussion in 'Misc Electronics' started by Cass Lewart, Dec 7, 2003.

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  1. Cass Lewart

    Cass Lewart Guest

    Can NiCad chargers be also used for NiMH batteries? If not what
    precautins should be taken? Most chargers cut off around 1.4 Volt which
    is ok for both kinds of batteries.

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  2. CWatters

    CWatters Guest

    Yes and no.

    It's not a good idea if the charger is a fast charger (>2C for example ).

    Good quality fast chargers for this type of cell use a technique called
    Delta V cut-off. This relies on the fact that (when charged by a constant
    current source) NiCad and NiMH cells have a characteristic voltage "peak"
    and subsequent slight _reduction_ in voltage when nearly full. The
    reduction in voltage is small and filtering must be employed to remove
    noise. The peak is smaller for NiMH than it is for NiCad cells.

    This means that NiCad chargers can look for an absolute fall in voltage,
    whereas NiMH chargers have to be more sensitive and usually look for the
    gradient changing from +ve to -ve. If you use a NiCad fast charger on NiMH
    cells, there is a danger that the peak won't be big enough to trip the end
    of charge detector leading to a possible overcharge. However most chargers
    of this type use a timer or temperature sensor as a safety backup or
    similar.
     
  3. Tsau

    Tsau Guest

    At least Maxim MAX713 can charge both NiCd and NiMH batteries. I built one
    charger with that IC for my kids RC car. It is very simple and also seems to
    charge the battires well. No I'm going to build another charger with the
    same IC for NiMH batteries. If you know how to solder, I suggest you should
    check that IC. It needs only few additional components and is very simple to
    get it work.

    TSa
     
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