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Can i upgrade my UPS by replacing 4.5Ah battery with 200Ah battery?

Discussion in 'Power Electronics' started by SirLSD, Feb 27, 2017.

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  1. SirLSD

    SirLSD

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    Feb 27, 2017
    I am looking for a cheap way of relying less on grid power as I have a 5KW solar system for daytime but no storage system. I picked up a couple of free uninterrupted power supply systems from 2 computers at work. the better one is a 510W 850VA system that has a 66 min run time. I looked inside and the power storage is a small lead/acid motorbike style 12V 4.5Ah battery.
    would it be possible to unplug the little 12V battery and connect a huge 200Ah 12V battery so that my 66min run time is now a several hour run time. I can have a timer so that the unit recharges off the mains power point during the day and then the timer switches off at sun down and my tv etc runs off the "free power" until I go to bed, and then recharges the next day.
    or will the big battery stuff the UPS unit?
    thanks
    total novice btw.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    Yes and no...

    Firstly, it's likely that the bigger 12V battery will have sufficient voltage and current capability (pretty much by definition).

    So what could go wrong?

    1. The inverter may be specified for intermittent use, operating it for long periods could lead to premature failure.
    2. The charger in the unit may not be capable of charging the larger battery in a realistic timeframe.
    3. If the original battery was internal, there is no guarantee that the battery is isolated from the mains output. An external battery may float at a dangerous potential.
    It is not certain that any of these will happen, and there may well be other problems I haven't thought of.
     
    Last edited: Feb 27, 2017
  3. SirLSD

    SirLSD

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    Feb 27, 2017
    1 the inverter was free so premature failure doesn't matter to me.
    2 can I connect a second battery charger to the battery if its not charging in time to speed up charge hours so it charges during daylight hours? or I could just unplug the battery and plug a big charger onto it every day.
    3 I don't understand 3. the plastic box has a slide off panel that contains the plastic lead acid battery with 1 wire to the positive terminal and1 wire to the negative terminal. no earth wire or anything.
    thanks
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    Maybe, but one problem lies with my point (3) above. The other lies with the design of either or both chargers. Will they work in parallel? (I simply don't know)

    That should work. But it would be a PITA.

    The unit is designed to operate with the internal batter and the box closed. How do you know that the battery's +ve isn't connected to the live output? It's probably quite unlikely, and if your inverter has a big hefty transformer in it, it's pretty remote, but I can't guarantee it isn't so.

    If the inverter has a connection for an external battery you should be a lot safer. I can't imagine that anyone would have anything that unsafe exposed (or potentially exposed).

    Playing with the mains is dangerous. I'm not suggesting that what you want to do won't work, but there are lots of gotchas (did I mention that your inverter may produce a square wave output that some devices won't like?).
     
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