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battery charger speed question

Discussion in 'Electronic Basics' started by Xah Lee, Oct 14, 2005.

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  1. Xah Lee

    Xah Lee Guest

    i have two battery chargers. One takes 13 hours to charge, while the
    other takes about 4 hours.

    i'm curious, is there any draw-back with the faster charger? Is the
    faster one due to technological advance, or is there some trade off
    here?

    Both are branded RadioShak. The slower one is model Cat. No. 23-418A,
    bought around 2000. The faster one is called FAST CHARGER Ca. No.:
    23-043, bought around 2003. They charge AA sized rechearble Ni-MH
    batteries.

    Thanks in advance for answering.

    Xah

    ∑ http://xahlee.org/
     
  2. Hactar

    Hactar Guest

    "More heat generated in the battery" and "a bigger transformer is
    required" are the obvious drawbacks. I don't know how it affects total
    charge or lifetime.
    I would guess "more expensive" and maybe "a better understanding of NiMH
    chemistry" are (some of) the differences.
     
  3. w2aew

    w2aew Guest

    The faster charger simply charges with a higher current than the slower
    charger. There are potential problems with charging at higher
    currents. When charging at a low rate, there is little danger of
    overheating the batteries, or causing damaging internal pressure
    increases. When you charge with a higher current, these dangers can
    exist. The trick is to know when to terminate the charging cycle.
    NiMH batteries exhibit a subtle "flattening" or slight negative delta-V
    of the cell voltage when they reach full charge (much more subtle than
    the negative delta-V of NiCDs). Decent chargers will look for this
    "signature" to terminate the charging cycle. If you don't do this, you
    run the risk of overcharging, which can damage the cells (high
    temperature, pressure, etc.). The importance of proper charge
    termination increases dramatically as you increase the charging current
    (decrease the charging time). The slow 12+ hour chargers are
    essentially trickle type chargers that cause little or no cell damage
    with overcharging, so no charge termination is usually necessary.
     
  4. Greg Goss

    Greg Goss Guest

    I know that when I was buying a NiMH battery for my cell phone, they
    made a big issue that you had to buy a battery with the chip included
    to control charging rates. Because the charging rate was controlled
    by the battery, the $12 car charger was affordable.

    I don't know how that works for generic NiMH batteries like AA or
    such. Is the chip still "in the battery"? If not, then "better
    understanding" of the chemistry and the charging profile, and perhaps
    a more expensive chip to allow handling more power as it passes
    through the control chip.
     
  5. I expect that your cell phone battery is Lithium Ion, not Nickel Metal
    Hydride.

    Lithium Ion batteries are very fussy about how they are treated, and
    will apparently explode if mistreated, so they are not available as
    individual cells on the consumer market. Even companies that will
    rebuild battery packs of other technologies often won't touch LiI.
    No - NiMH batteries don't need a chip in the battery - the AA
    "batteries" are really single cells. (A battery _should_ refer to two
    or more cells connected together (usually in series.))
     
  6. Rich Grise

    Rich Grise Guest

    I don't understand the question. The "FAST CHARGER" charges the
    batteries faster. What seems to be the problem? ;-)

    Actually, it's probably just a matter of the available charge
    current, or it could be that sometime between 2000 and 2003 somebody
    implemented a faster charging profile algorithm.

    Hope This Helps!
    Rich
     
  7. Kitchen Man

    Kitchen Man Guest

    Well now, that's a little known piece of information that is nice to
    know! Thanks for the info.
     
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