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Battery Back-Up Systems

Discussion in 'Power Electronics' started by Nic, Nov 3, 2012.

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  1. Nic


    Oct 29, 2012
    I have an old battery back-up system for a household computer which uses a 12 Volt battery.

    I want to substitute a 12 Volt deep cycle marine battery and use is as a backup for the electric sump in my basement.

    I'd like some guidance on selecting the correct battery for the job. Since the sump is on a float switch and doesn't run full-time, I thought with the right battery, I might be able to get many hours of battery back up.

    So again; I know that the pump is 9 amps. What else must I take into consideration? If I wanted 24 hours of back up, How do I determine the number of batteries needed?

    How would you approach this project?

    Thank you in advance.
  2. CocaCola


    Apr 7, 2012
    You have to establish an estimated duty cycle of the pump to get a valid backup time...

    For quick and dirty, lets assume stormy weather where the pump will be cycling on/off, so lets say it's on 50% of the time...

    So @ 9A and 50% of the time you have a drain of about 4.5A an hour... Times 24 hours is 108Ah... But, you have to factor in the fact the world is not perfect and thus a 150Ah battery would probably be closer to a real world 24 hour run...

    If the pump is to run 100% of the time you would need a 216Ah (perfect world), and so on and so on...

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    I'd advise you to check the specs on your UPS. They come in vastly varying capacities. I doubt that one made for a single PC is up to the task of driving a 9A pump motor. The start current can be over twice its run current. It's also a highly reactive load.

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