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charging NiMH vs NiCad

Discussion in 'Misc Electronics' started by Brian O, Mar 31, 2006.

  1. Brian O

    Brian O Guest

    Is there much difference in the way these batteries should be charged? I
    have a portable radio that has a charger that tricklecharges NiCads, D
    cells. Could NiMH be used in place of the NiCads without chance of damage
    to the cells or to the radio? Any help is appreciated. Thanks.
    B
     
  2. JeffM

    JeffM Guest

  3. Brian O

    Brian O Guest

    http://groups.google.com/groups/sea...NiCd+charge+OR+charger+OR+charging+OR+charged

    Thanks for the link. I found an answer that makes sense, unlike some of the
    help that was offered in here....

    "Asking about the difference between NiCd & NiMH battery chargers -


    The Cadex site (www.cadex.com) says that there are important
    differences between the chargers. They claim that:


    The charge termination criterion is different. Most NiCd chargers
    stop (or transition to trickle charge) on a characteristic voltage
    drop. The NiMH voltage drop is more subtle. Most NiMH chargers
    transition based on temperature.


    The NiMH cell requires a smaller trickle charge. "A trickle
    charge that is acceptable for the NiCd will overheat the NiMH and
    cause irreversible damage."
     
  4. CWatters

    CWatters Guest

    The answer is only "possibly".

    How do you tell if a nicad is full...well the voltage drops ever so
    slightly. Many chargers look for this drop and switch off. If that fails
    they have a safety timer as a backup. NiMH cells have a much smaller voltage
    drop and the a NiCad charger can fail to detect it. In a fast charger this
    can result in the cells being over charged and damaged (a fire even). In a
    trickle charger the safety timer may or may be triggered before the cells
    are charged.

    So in your case the most likely outcomes are either:

    a) It all works ok
    b) The cells are overcharged, get a bit warm/hot and their life may be
    shortened.
    c) The cells may never be fully charged because the safety timer kicks in.

    If you house burns down - remember that I recommend you buy a charger
    designed for NiMH cells. They aren't very expensive and sometimes come with
    free cells.
     
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