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Car battery & pool sump pump Amperage/life question!

  1. Dec 14, 2009 #1
    Alright, so here goes, and by the way, this isn't homework, just in case you're wondering.

    Question 1: So, i have a 12vdc 500amp battery/car inverter and a 12vdc 11amp sump pump. If I wire it up, approximately how long will they last?

    Question 2: Also, I have a power inverter for my car, can I hook up a 120v 11amp sump pump to it and connect it directly to the battery without resistance? That is wire the inverter directly to the battery? I'm not sure how cigarette lighter plugs work, but as it stands the inverter has a cigarette lighter plug on the end.

    Answers are welcome, but please: Feel free to spit out a formula and explain the variables fully!

    Last edited: Dec 14, 2009
  2. jcsd
  3. Dec 14, 2009 #2
    For Question 2, what is the output Amperage rating of the inverter?
  4. Dec 14, 2009 #3
    I'm not totally sure, it's faded off the label. but I ran a small 17" tv off of it along with the original Xbox. So im sure that the pump shouldn't take more current than them.
  5. Dec 14, 2009 #4
    The TV is not enough of a test load. The sump pump needs about 1300 Watts. A small TV draws, what?, 300 Watts max?

    In any case your 12V sump pump is a much lighter load. It's 1/10th the load of the 120 volt job.
  6. Dec 14, 2009 #5
    Thanks dude, I forgot to specify the AH of the battery. It's 14AH. I appreciate you posting and replying.
    It's weird, because i thought for sure i'd be able to figure this out, haha.

    Now that I think about it, I have a car booster as well, rated at 14AH as well!
    Would running the pump for any extended period of time harm the car booster if ran for a period of 15 minutes to a half hour?
    Last edited: Dec 14, 2009
  7. Dec 14, 2009 #6
    OK. You will get the same energy out of the battery, whether you convert it to 120VAC or use it directly. The conversion to 120VAC will cost some overhead energy in converions. Anyway, A 14AH battery will have about 14A*12V = 168 Watts for one hour. It's a bit less as the 12 volts decays toward 10 volts. Call it 150 Watt for one hour.

    Using the 12 volt pump at 11 Amps, it will run for maybe one hour and 15 minutes before the battery is depleted if the battery is new at full load. One hour if it's less than new. Even better for you it's rated at 11 Amps under full load. You may not always be running near full load. But bad for you, the pump may not be able to pull a column of water from the bottom of the pool to the pump.

    Wire the pump to the battery. Put the pump in a bucket of water and the outlet raised up. Raise the outlet tube so that the end is the same as pumping from the bottom of the pool and see if it complains.
    Last edited: Dec 14, 2009
  8. Dec 14, 2009 #7
    Wow, I appreciate it! :D. Been a learning curve! I've had this account for a while now, but im glad i kept on the newsletter and kept it around, it has come in great handy!

    the pumps max is 11amps

    I greatly appreciate it Phrak! Turns out the sump pump is a little on the cheap side, can only run for half hour intervals, cuts out every half hour for about 15 minutes. Has a 240GPH flow rate, if anyone is wondering. Also future note, buy a better sump pump!

    Mind jotting down the formula though with an explanation? Thanks!

    Cheers mate!
    Last edited: Dec 14, 2009
  9. Dec 15, 2009 #8
    You're welcome XsnidalX. I don't really know what formula's I've used except P=EI, power = voltage x amperage. --That and some general engineering skill--though I haven't done a lot of motor applications.
  10. Dec 16, 2009 #9


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    Assuming this is not a typo, I really don't think you should do this. 11A at 120V is a lot of power to draw from a battery. It won't last more than a few minutes. If you run the car while it's drawing this much power, it will destroy your alternator.

    I should probably ask how much you paid for the inverter. Power electronics are very expensive so if you paid anything less than $200 then the inverter probably won't support 11A. The cheapest one on Newegg capable of doing what you're asking is $400. The next cheapest model on that site is $280 but only supports 750W continuous.

    I'm assuming you're doing this because you don't have access to a regular house receptacle. In that case, get a gasoline generator and use that. A 2700W generator costs $300 CDN at my local hardware store.
  11. Dec 16, 2009 #10
    I'm not sure if I've read the question correctly but what is the inverter for? the pump seems to be 12vdc?
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