Connecting a 12V 800VA Inverter to a7Ah battery

Discussion in 'General Electronics Chat' started by Philosoph3r, Oct 11, 2015.

  1. Philosoph3r

    Thread Starter New Member

    Oct 11, 2015
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    0
    I need some help with a power backup situation I have.

    I have a 800VA inverter that used to be connected to a 12V 800VA 150Ah lead-acid battery. To be brief, the battery died because it was not used for a year or so.

    I now have the need to have some power backup for my computer. All I need is about 5 minutes of backup at any time to cover for when the apartment's generator kicks in. So I figured I could just get a smaller UPS battery with 12V 7Ah capacity.

    The question is, can I connect the inverter to this smaller battery?
    Thanks in advance!
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,233
    619
    As long as you adjust the load you put on the inverter to account for the lower capacity battery.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,984
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    Yes, as long as the battery has sufficient capacity to power your computer for 5 minutes.
    What is the total power level you need to backup? (For maximum backup time you should power only the computer from the inverter, not any auxiliary stuff such as the monitor).
    You can get no more than perhaps about 50% of the battery capacity at the output of the inverter before it dies.

    Note, that to prevent future battery failure, you will need to trickle charge the battery continuously when the inverter is off.
    Lead acid batteries do not like being left uncharged (they sulfate).
     
  4. Philosoph3r

    Thread Starter New Member

    Oct 11, 2015
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    0
    Yep, I am sure the battery can handle it. The computer has a 550 Watt SMPS although I am sure the load at any time does not exceed 300 Watt.

    I am just worried whether the inverter itself would be able to regulate a lower powered battery.
    Essentially what I want to do is connect this to this.

    Yep, lesson learnt the hard way. I will trickle charge batteries if they have to lie around in the future.
     
    Last edited: Oct 11, 2015
  5. crutschow

    Expert

    Mar 14, 2008
    12,984
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    The one problem I see with using such a small battery is how well it can deliver the high current needed for a 300W load (likely over 30A when considering the inverter efficiency).
    Its lifetime may be less than 5 minutes under such a load.

    You need to carefully look at its capacity spec under such a high current.
    It may be significantly less than 1/2 of its rated capacity which is given at a light (10 hour) load.

    Also if you can measure the actual computer current, that would help in the estimate.
     
    Last edited: Oct 11, 2015
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