How long to charge AA NiMH?

Discussion in 'Digital Photography' started by Ed Wicks, Dec 28, 2006.

  1. Ed Wicks

    Ed Wicks Guest

    I have a Sony BC-CS1 charger. Apparently the charging light never goes
    How long should I charge a AA NiMH battery? Thx. Ed
    Ed Wicks, Dec 28, 2006
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  2. Ed Wicks

    Cgiorgio Guest

    Until it is fully charged. When charged with a fairly high current (greater
    than about 1/4th of capacity), NiMH batteries start to heat up, (most of the
    energy is converted to heat) and the terminal voltage drops slightly. Decent
    chargers will detect this state for every single cell and either switch the
    charge current off or switch to trickle charge for maintaining the charge. I
    do not know about the Sony BC-CS1. For example the better models from GP and
    others work fine this way. As a rule of thumb, a fully discharged new NiMH
    battery can be charged with 1.4 times its capacity before overcharging sets
    Cgiorgio, Dec 28, 2006
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  3. Ed Wicks

    Bob Salomon Guest

    Until it is charged. How long does that take?

    Take the mAh rating of the battery. Add 30% and divide that by the
    chargers output. That is how long it takes that charger to recharge that
    battery if that cell is fully uncharged.
    Bob Salomon, Dec 28, 2006
  4. The NiMH batteries are known for high tolerance to overcharging. If you
    charge your battery for 8 hours, it will definetely be charged (there
    are no other chargers which are made for charging for longer).
    =?iso-8859-1?B?bWlubmVz+HR0aQ==?=, Dec 28, 2006
  5. Ed Wicks

    Mardon Guest

    Close but not quite. The "Operating Instructions" sheet packed with my
    Sony BCG-34HUF charger specify a 15 minute charge time for 2500mA NH-AA
    batteries. The charging output is specified as 7.5 amps at 5.6 volts DC.
    You formula calculates 26 minutes. If you deduct the 30% instead of adding
    it, the formula calculates 14 minutes. Did you mean to say "add 30%" or
    should it have been "subtract 30%" or does this particular charger just
    work faster than your formula?
    Mardon, Dec 28, 2006
  6. Ed Wicks

    Ken Weitzel Guest


    That charger is little more than a trickle charger; it charges at only
    70 mil's. So if you were charging 2500 mA batteries from "empty" to
    completely topped up, it would take a little more than two days to finish.

    Take care.

    Ken Weitzel, Dec 28, 2006
  7. Ed Wicks

    ASAAR Guest

    How long have you waited for the light to go out? Some old
    chargers have lights that don't indicate when the batteries have
    reached a full charge, and use the light only to indicate that the
    charger is powered on and is still charging, even if the batteries
    have been charged so long that they're now being overcharged.

    A figure can't be given for that charger unless you know the
    actual capacity of the AA batteries. The BC-CS1 is an old, *slow*
    charger that took 13 hours to charge 1,750mAh AA batteries. If you
    have the original AA cells that came with the charger, they're
    probably pretty old and have lost a lot of their original capacity.
    So if by now they're providing only 1,200mAh, they'd charge quicker,
    taking about 9 hours to reach full charge. But if you buy new
    2,700mAh batteries, they would need just over 20 hours to complete
    charging. Such old chargers usually had timer cutoffs, so that they
    might stop charging after about 15 hours, and the 2,700mAh batteries
    wouldn't fully charge with only a single charge cycle. If the
    charger's charging light went out at 15 hours, the 2,700mAh
    batteries would only be 75% charged.

    You should probably get a new "smart" charger, one that knows when
    the batteries are fully charged and stops charging at that point,
    instead of continuing to charge until a time limit is reached.
    They'll be able to deal with modern high capacity NiMH cells, and
    depending on the model, can fully charge AA cells in less than a
    couple of hours. There are some very high current chargers that can
    fully charge AA cells in as little as 15 minutes, but the NiMH
    batteries would probably last longer if you get a gentler charger
    that takes an hour or more to finish charging.
    ASAAR, Dec 28, 2006
  8. Ed Wicks

    Paul Allen Guest

    Here's the summary I wrote up back in 2002, including a link to
    definitive backup material by Marc Venis and a handy Java charging
    time calculator:

    Charging time does matter. If your charger is not one of the newer
    automatic types, you must know the charging current and the capacity
    of your batteries in order to calculate the approximate time to a
    full charge. If your charger does not have its charging current
    listed on its label, throw it out and buy a better one.

    Paul Allen
    Paul Allen, Dec 28, 2006
  9. LOL I got my first N-Mh AA 2600mA cells last week and only have an old
    Uniross charger which states it charges at 150 mA.

    I make that around 24.6 hours for a full charge! Must get a modern

    The rule of thumb I used with slow charge Ni-Cd's is capacity/10 for 14
    Just Another Digital Fan, Dec 28, 2006
  10. Ed Wicks

    Freedom55 Guest

    I have 2500 NiMH batteries which take 27 hours to charge in my 140mA


    And it really doesn't matter if
    I'm wrong I'm right
    Where I belong I'm right
    Where I belong.

    Lennon & McCartney
    Freedom55, Dec 28, 2006
  11. Check with Sony. Chargers are all different, some
    are 15 minute chargers, others 1 hour, some are
    set for much longer times, some are adjustable.
    If the batteries are more than just warm and start
    getting hot, they are still being charged so take
    them out.
    George E. Cawthon, Dec 28, 2006
  12. This unit is rated at 165 mA per cell.

    Most AA NiMH cells are rated at around 2800 mAH. Hence, a complete
    recharge would take about 17 hours. Most charges heat the cells up
    until they go on trickle charge, so if the cells start cooling down,
    that should mean they are charged.
    Stephen Henning, Dec 29, 2006
  13. While it is true that 2800/165 = 17 hours this would result in a semi
    charged battery. The losses due to heat etc would need to be added to
    give a correct charging period and would be more like 24 hours for a
    full charge.
    Just Another Digital Fan, Dec 29, 2006
  14. Ed Wicks

    Ed Wicks Guest

    Thanks to all for the education on this subject. I went out and bought
    a new charger and new batteries, and all is well. Thx again.
    Ed Wicks
    Ed Wicks, Dec 31, 2006
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