Nimh chargers have limits?

Discussion in 'Digital Photography' started by JakeC, Feb 12, 2007.

  1. JakeC

    JakeC Guest

    Hi all again:

    Just a short question: can I use a charger for batteries up to 850 mAh
    AAA batteries to charge AAA batteries of 900 mAh?

    JakeC, Feb 12, 2007
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  2. JakeC

    Paul Rubin Guest

    They might end up not getting fully charged, at least by the time the
    little light goes out (or whatever). Chances are they will keep
    trickle charging, and leaving them on overnight will fully charge
    them. The 850 mah limit is to prevent overcharging.
    Paul Rubin, Feb 12, 2007
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  3. JakeC

    Lionel Guest

    It depends on the charger. Any "intelligent" NiMH charger should work
    fine with any cell capacity. And the difference between 850mAh &
    900mAh is so tiny that it shouldn't be a problem with even the
    simplest charger.
    Lionel, Feb 12, 2007
  4. JakeC

    Daryl Bryant Guest

    You can, but it may not be able to fully charge the battery.

    The charger should say what the output is, unless it's a pulse charger. A
    pulse charger is smart enough to figure out what the total battery output
    is, and thus will charge the batteries sufficiently.
    Daryl Bryant, Feb 12, 2007
  5. JakeC

    ASAAR Guest

    You shouldn't have to worry about it, even with higher capacity
    ones such as the 1,000 mAh NiMH batteries that have been sold for
    several months now. If you have a "smart" charger, it will stop
    quick charging when it senses that the AAA cells are just about
    fully charged, and then drop to a much slower, or trickle charge
    before its job is done. These time that these chargers need to
    charge fully depleted batteries depends on their design and ranges
    anywhere from 15 minute to 6 or 7 hours. When you get in to 10 hour
    (and longer) territory, you're probably dealing with a "dumb"
    charger that doesn't know when the batteries will have finished
    charging, so they just keep charging until an internal timer stops
    the charging.

    The reason why you don't have to worry about higher capacity
    batteries not getting fully charged (within reason) is due to two
    factors. First, every dumb charger that I've used was designed with
    a particular capacity battery in mind, and used a timer shutoff
    delay much greater than necessary for a full charge. So if the
    charger documentation indicated that it would fully charge batteries
    in 11 1/2 hours, it might have the timer shut down the charger after
    14 hours. While overcharging isn't the best thing to do to
    batteries, at such low charge rates you don't have to worry about
    the severe damage that would occur from overcharging batteries at
    much higher charge rates, which could cause tremendous overheating.
    In addition, batteries lose capacity with age and with use, so after
    several months, those new 1,000 mAh AAA batteries if tested, might
    only have an actual capacity of about 850 mAh remaining anyway. :)

    If you don't have the charger's literature that shows how fast it
    charges, or whether it's a "smart" charger or not, you'll probably
    be able to download its manual from the manufacturer's website.
    ASAAR, Feb 12, 2007
  6. JakeC

    Ron Hunter Guest

    It depends on how the charger determines when to stop charging. If you
    have a charger that just times the charge, discard it! If it just takes
    longer to charge the higher capacity batteries, it is fine.
    Ron Hunter, Feb 12, 2007
  7. JakeC

    tnom Guest

    I take it you have 850mah AAA batteries and want to use a charger
    rated at 900mah. If so yes you can use it. What brand is it. It sounds
    like a quick charger that will charge your batteries in one hour and
    then shut down or go to trickle charge.
    tnom, Feb 12, 2007
  8. JakeC

    JakeC Guest

    Actually, it's one of those chargers that come with the energizer
    batteries. It says it's for up to 850 mph AAA. Then I found out a local
    shop only sell 900 mph AAA.

    If they keep pushing the mph up, does that mean I have to upgrade my
    charger every year?
    JakeC, Feb 13, 2007
  9. JakeC

    AnthonyL Guest

    My old energiser which came with 1500mah batteries does nothing when I
    put 2300mah batteries in it. The charging lights do not come on at
    all :(
    AnthonyL, Feb 13, 2007
  10. JakeC

    Ken Lucke Guest

    I wish _I_ could get 900 mph out of _my_ AAA's. It'd cut my travel
    times down /tremendously/.


    You need only reflect that one of the best ways to get yourself a
    reputation as a dangerous citizen these days is to go about repeating
    the very phrases which our founding fathers used in the struggle for
    -- Charles A. Beard
    Ken Lucke, Feb 13, 2007
  11. JakeC

    tnom Guest

    Don't worry about getting another charger until the 850mah charger
    dies. If you put a substantially bigger mah battery in the 850mah
    charger then the worst that can happen is the charger will fry. It
    will not explode or burn. It will just stop working.
    tnom, Feb 13, 2007
  12. JakeC

    Just D Guest

    That's exactly happened to my charger that I bought several years ago and it
    was made to charge batteries up to 1100 mAh. When I tried 2300-2500 it tried
    to charge them couple times, but then suddenly stopped working, one port
    after one. It was having 4 independent ports for AA, AAA and one 9V battery.
    The whole set just stopped working and I guess it overheated.

    The new one that I had to buy after this one is a little bit more
    intelligent Sony BCG-34HRMF, works from 100 to 240 V, etc, but doesn't have
    a 9V charger, which I'd use if I had. Also it's funny, but it has some

    Output 1.2V

    1050 mA (AA) x 2
    525 mA (AA) x 4
    640 mA (AAA) x 2
    320 mA (AAA) x 4

    I guess it's good because otherwise I could put a tear pot on it and/or it
    would be dead in a short period of time like the first one. Also this one
    doesn't have any external trans.

    Just D.
    Just D, Feb 13, 2007
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