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UPS battery upgrade

Discussion in 'Electronic Basics' started by JazzMan, Aug 23, 2005.

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  1. JazzMan

    JazzMan Guest

    Any fundamental reasons why I can't use the guts of my
    Tripplite 800 UPS with a larger external battery?

    JazzMan
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  2. Guest

    Because the power supply on the powergrid side may not handle the load to
    charge that much. A dirt hack would be to have relays to switch batteries in
    and out. So that powersupply never is overloaded.
     
  3. JazzMan

    JazzMan Guest

    If the charging circuit is current limited, with voltage
    level used to switch from charging to maintenance, wouldn't
    the net result be that it takes longer to charge a larger
    battery? Also, I assume that the charging cycle generates
    less heat than the discharge mode, so presumably the
    additional time charging wouldn't present any problems.
    Would that be a good assumption?

    As far as discharge, I guess the inverter heating is a
    function of load vs time, with the system designed to
    withstand its maximum output with the stock battery. I
    can retrofit a cooling fan quite easily.

    The reason I'm considering this is because I already have
    a battery, it's about the size of a car battery but it came
    out of a whole office UPS system and is designed for UPS
    duty, and the battery just kicked the bucket in one of my
    Tripplites. I can't afford to buy a new proper size battery,
    but can kitbash something together that's ugly but functional.

    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
    **********************************************************
     
  4. Jasen Betts

    Jasen Betts Guest

    check the owners manual.

    some UPSs can't handle running their charging circuit for a
    long enough time to charge a large external battery - the
    charger overheats and dies which ruins the UPS.
    Other UPSs can, typically the big expensive ones.

    Bye.
    Jasen
     
  5. Jasen Betts

    Jasen Betts Guest

    No.
    lead acid batteries are typically charged with constant voltage chargers, so
    the charger will see a larger load. _if_ there is current limiting in there that
    part will be working harder and it will get hotter...

    the charging circuit uses separate parts from the discharging circuit.
    it depends how finely they cut the margins when they designed it...

    it may be fine,or putting bigger heatsinks in the charger section may be all
    it takes.
    Bye.
    Jasen
     
  6. ehsjr

    ehsjr Guest

    P, the power dissipated as heat in the limiting part, is equal
    to the current, I, times the voltage across the limiting part.
    The equation is P=VI

    V is the voltage across the limiter, equal to Vin, the constant
    voltage source, minus the battery voltage, which is the voltage
    specified to meet the requirements of the UPS, and therefore
    the same for the larger battery as for the original battery.
    I is the limited current, and is the same for both batteries.
    So P=VI will result in the same number for either battery.
    The limiting part won't work harder and won't get hotter - but
    it will take longer to charge the larger battery, as the
    OP presumed.

    Ed
     
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