Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Battery life using 6000 watt inverter

  1. May 15, 2016 #1
    I have four 125 ah batteries powering a 6000 watt inverter. The inverter is supposed to have a no load draw of 2 amps. I have a 12 amp 120volt Ac load. How long should I be able to operate before drawing my batteries to 50%
  2. jcsd
  3. May 15, 2016 #2
    By the way, the batteries are 12 volt deep cycle. They are connected in parallel
  4. May 15, 2016 #3


    Staff: Mentor

    Using very rough numbers, about 2 kwh from those 4 batteries.

    A better way to express it is to recharge whenever the loaded voltage drops below 12V, of 12.2V when rested and at no load.
  5. May 16, 2016 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The output of the inverter is..
    12A * 120V = 1440W
    If the inverter was 100% efficient then the input would also be 1440W but that's unlikely. Efficiencies of >80% are possible. Using 80% that gives an input power of

    1440/0.8 = 1800W
    At 12V that's a current of

    1800/12 = 150A or 37.5A per battery.

    You say they have a nominal capacity of 125AH but only want to use 50% so they can deliver that 37.5A for
    125/(2*37.5) = 1.6 hours. Call it 90 mins.

    Your mileage may vary! Check the actual efficiency of your inverter.

    Put the inverter as close as possible to the batteries and use fat cables. At 80% efficiency the inverter dissipates 1800-1440 = 360W so allow for cooling air flow.

    I used a lot of lead acid batteries in the 1980's amd 90's. I found the key to long life is never to leave them discharged for long, get them back on a charger as soon as possible, ideally within hours of use. I found if you regularly left one party discharged for a week they didn't last long, well under a year. Once I got into the habit of leaving them on a float charger all the time they started to live a lot longer.
  6. May 17, 2016 #5


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Batteries connected in parallel should be of the same type and the same age or they will (very likely) 'age' prematurely. Charge and discharge currents will not be shared equally if you use different batteries and using four random batteries can be false economy even if you get them cheap. Your deep cycle choice was good. The only good thing about car start batteries is that they can give you hundreds of Amps when needed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted