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How to calculate how fast it would take to charge/discharge a battery

  1. Sep 3, 2011 #1
    I was wondering if it was possible to use, simultaneously, a 30 amp (or higher) charger on a car battery and a DC to AC (say, 700 watts) power inverter.

    Where I live we have 8 to 10 hours of power outages in 2 hour intervals during the day. Instead of wasting money on expensive office UPSes, I was wondering if I could make something a bit more sturdy using cheaper car batteries.

    What I wanted to know is, how fast would a 30 amp charger take to charge a car battery? And how long could a car battery deliver 700 watts? I'm a complete n00b here so if someone could point out the specific formula/equation to use to calculate this, I would greatly appreciate it!

    Ideally I would like enough batteries (I could just hook up a bunch of them up in parallel?) to deliver 700 watts for 4 hours, that would then recharge within 2 hours (when the power's back on).

    Lastly, does anyone have tips for actually setting up this kind of apparatus? Specific parts/companies?
  2. jcsd
  3. Sep 3, 2011 #2
    It looks like what you really want to build is an inverter.
  4. Sep 3, 2011 #3


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    Gold Member

    I can't answer your question but I do caution you to exercise care in designing battery recharging devices because if you recharge too quickly (on some batteries at least) you may get a charge a few times but will quickly destroy the battery due to overheating then you will have lots of acid-filled door-stops on your hands (and that's assuming they don't explode --- I'm not positive they do that but it wouldn't surprise me)
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