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Building a 500 cell NiMH battery pack, 15 Ah @120V?

Discussion in 'Electronic Basics' started by JazzMan, Jan 4, 2006.

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  1. JazzMan

    JazzMan Guest

    I was toying around with what it would take to
    build a 1.8 KWh (15A @ 120V for 1 hour) battery
    pack. So far I'm at around 500 AA 3,000 mAh
    batteries, but how to connect them up? I bet
    that 5 x 100 cell series sets in a 5-wide parallel
    array wouldn't work, where does one start with
    something like this? I don't have a particular
    project in mind, well, maybe, but this is more
    of a mental workout.

    JazzMan
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  2. gcd

    gcd Guest

    Hi,
    Have you considered using a DC-DC converter or DC-AC inverter for your
    application, may be a lot simpler.

    Maybe even 10 sealed lead acids may be a better choice?

    If you want to parallel stacks then you will need to isolate them from each
    other using diodes or similar so one stack doesn't try to charge a weaker
    one. As the load increase and the terminal voltage drops on the highest
    voltage stack the others will eventually load share.

    Also, you can load NiMH cells to about 2C. This will reduce capacity to
    around 80% with reasonable terminal volts but would reduce the number of
    stacks needed to be paralleled. However the downside is the cell dissipates
    more power. You can load to higher than 2C but usually done in motor
    applications such as Radio Control and the capcity decreases rather quickly
    for higher loadings, check googgle for "discharge rates for NiMH".

    Depending on your application Li-Ion or Li-Ion polymer may be a better
    choice - higher power densities.

    Good luck making a charger for that :)

    of course no need to mention the safety aspects is there?

    Cheers
    Greg
     
  3. Pooh Bear

    Pooh Bear Guest

    Why AA ? Surely D cells would be simpler ?

    Graham
     
  4. BobG

    BobG Guest

    This is what AC Propulsion uses for the TZero. They make packs the size
    of cigar boxes out of em and have em everywhere.
     
  5. JazzMan

    JazzMan Guest

    I arbitrarily chose AA because those are commonly
    available, though it appears not in the 3000mAh that
    I originally thought. If I get serious about this I
    will do calculations on price/mAh to get the best
    value irrespective of size. I'm shooting for a pack
    that weighs less than 60 lbs including charging. For
    charging I was going to use a dedicated charger
    circuit for each series of cells, implementing one
    of the advanced charge strategies, along with
    temp sensing for each series set.

    JazzMan
    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     
  6. Jasen Betts

    Jasen Betts Guest

    I was kind of suprised when you wrote that, I'd just been to the battery
    shop for new cells for the digital camera and they guy said that the
    Sanyo 2500mAh cells he sold me were the highest capacity he also said
    that cheap cells were crap but the Sanyo cells didn't strike me as being
    expensive.

    Bye.
    Jasen
     
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