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sizing a battery charger

Discussion in 'Photovoltaics' started by Robert Morein, Jun 5, 2004.

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  1. I'm building a system that will have PV for disasters, and an AC charger to
    quickly replenish the batteries after a blackout.

    What is the convention for sizing these chargers for use with golf cart
    batteries?
    A charger spec for a 2 or 3 state charger gives the maximum "bulk" charge
    rate.
    I can choose
    (http://www.donrowe.com/battery_charger/samlex_batterycharger_12v.html)

    between a 15, 30, or 45 amp charger.
    However, the 15 and 30 can charge a battery while still drawing current from
    the inverter, functioning as a UPS.
    The 45 cannot, because the charging algorithm can't sense state of charge
    under those circumstances.

    The batteries will be the standard 220 ah 6v, series-paralleled into one 660
    ah 12V bank.
     
  2. George Ghio

    George Ghio Guest

    C10 rating.
     
  3. daestrom

    daestrom Guest

    If the batteries are only going to be used rarely, consider whether
    'golf-cart' batteries are the right choice. These are typically deep-cycle
    lead-antimony style intended for a large number of deep cycles. But you
    seem to be saying the application is only for rare power outages and the
    batteries will be on 'float' most of the time from an AC charger.

    This is a different sort of application than many solar PV setups and can
    benefit from a different type of lead-acid battery. Large cell 'station
    batteries' and other UPS-like batteries with lead-calcium grids can handle
    fewer deep cycles, but will provide years of service if kept on a float
    charge most of the time (longer than lead-antimony in the same application).

    The charging charicteristics are somewhat different between these types and
    your charger would have to be for the correct type.

    daestrom
     
  4. Thanks for your reply.
    I'm designing not just for ordinary power outages, but also for a range of
    terror disruptions.
    If it was simply a case of a typical power outage, I could simply run the
    generator.
    However, an extended disruption would use a lot of fuel, and wear out the
    generator.
    The design envisions a one month power outage, where the battery bank would
    be repeatedly cycled, and topped off by the generator.
    In this usage, lead-calcium would rapidly fall apart.


    If fuel supplies become inadequate, I have purchased two 100W solar panels,
    and a 20 amp charge controller.
    However, an AC charger would need to be larger to minimize generator
    runtime.

    I thought that these batteries could be bulk-charged at very high rates, but
    comments have suggested C/10 as a goal.

    In another thread, I asked about the lifetime of golf cart batteries on
    float, ie., zero discharge/charge cycles.
    An authoritative answer would be very useful.
     
  5. And it turned into a real rathole, because you never clarified your
    application. Batteries that have zero cyles have an infinite
    lifetime, because they always supply all the power required of them.

    To answer the question you didn't ask, Trojan specifies their
    batteries in terms of Lifetime Energy Units (#define "kilowatt hours a
    battery delivers over it's useful life"), and T-105s have 438 of them.
    If you use them at 100% DOD or 1%DOD you'll get the same lifetime
    (claims Trojan, who ought to know).
     
  6. Guest

    Maybe they've changed their tune. The T-105 DOD vs #cyc curve they faxed
    me shows about 750 cycles at 100% DOD (LEU = 473 kWh), 1000 at 70% (441),
    1500 at 42% (397), 3000 at 20% (378), and 5500 at 10% (347), so fewer
    batteries with larger DODs would optimize the LEU and cost per kWh,

    This makes sense to me, since batteries do have a limiting shelf life,
    even with no discharging...

    Nick
     
  7. Very useful, thanks.
     
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