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NiMH cells emit smell of gas

Discussion in 'Electronic Equipment' started by Jon D, May 22, 2006.

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  1. Jon D

    Jon D Guest

    I have a rapid charger with a fold down cover. When I charge a couple
    eof AA or AAA cells there is a smell of gas in the chamber under the
    lid.

    Seems to me that the cells are getting overcharge and are venting.

    This is a charger with a sensor for "negative delta-V" to edermine the
    end of the charging. The cells are about 10 to 15C above room
    temperatre.

    Is the charger cooking my cells? Or is the smell noticeable because of
    the enclosed battery compartment?
     
  2. kony

    kony Guest

    Possibly the cells had vented previously and the seal is now
    open. I would throw them away, then wonder why they'd
    gotten hot enough to vent previously. Some Delta-V chargers
    only have a Delta-V detection but not temp monitoring, so if
    a cell were fully charged and an event like AC power flicker
    occured at long enough duration to reset the charger, it
    might then start charging at the fast-charge rate again, but
    there will be no Delta-V to detect since the cells were past
    that stage already... so if they get too hot, they vent
    which was better than an explosion.

    At the very least if you continue to use that charger, you
    might not want to fold down the cover to increase passive
    cooling. There are other things you could do like pointing
    a fan at the cells but it seems a hassle instead of just
    seeking a different charger, IF it seems the charger doesn't
    have the temp cutoff feature.


    No with undamaged cells and proper charging (not
    overcharging) there is no gas escaping to be building up in
    the compartment.
     
  3. UCLAN

    UCLAN Guest

    You need a better charger, like a Maha MH-C401FS.

    http://www.thomas-distributing.com/mhc401fs.htm
     
  4. Not all cells can be rapid-charged, some have just too high impedance
    for that, as result they would heat up and went.
    Good rapid chargers come with the cells designed for rapid charging,
    or must at least have a list of recommended cells.

    Regards,
    Evgenij
     
  5. Guest

    deltaV doesn't work very well with NiMH cells because NiMH voltage
    either doesn't drop or drops only a very small amount when full charge
    approaches.

    Some chargers are much worse than others. The best use not only deltaV
    but also temperature, temperature difference, rate of temperature
    rise, and, as a last resort, time.
     
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