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  1. #1
    Member DUSNOETOS's Avatar
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    Car battery powering a laptop??

    OK,
    It is looking like my wife is gong to give me a much needed few days to my self.....And I am thinking about going camping before the weather becomes unbareabale....

    I want to take my laptop (not concerned about not having INTERNET access) but I know my battery is getting weak. Does any one know how long one could run a laptop off of a car battery (say 550 amp battery) unsung an inverter??

    My laptop is a IBM T30 think pad.

    (and the camp site I am thinking about going to does not have electricity )
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  2. #2
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    thideras's Avatar
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    I'm not quite sure if it works, but that is an awesome idea and I like how you think! Now you just need to hook it up to your phone and get internet!
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  3. #3
    Member DUSNOETOS's Avatar
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    i know that it works, I have a 100 watt Black and Decker inverter that runs my laptop just fine....I usually use it on car tripps, but while the car is running... I know that the inverter will run my laptop straight off of the car battery but what I am trying to figure out is....How long can I run the laptop before the car battery discharges enough that I would have trouble starting the car??

    the battery in my car is 1000 amp (850CCA)
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  4. #4
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    If you know the mA rating for the laptop and battery, you should (in theory) be able to figure out how long it should last. I honestly don't know how you would calculate it with a car battery though...
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  5. #5
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    Rough estimate:

    120V x .7A = 84W

    84W/12V = 7A (DC)

    7A X .1 (inverter consumption, estimated) = .7A

    total DC load = 7.7A

    1000AH/40 (max safe discharge for lead acid = 40&#37 = 400AH

    400AH/7.7A = 51 hours

    You could probably push it to 67hours/50% discharge, but that may be a bit rough on the battery.
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  6. #6
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    I built something very similar with an added solar panel to charge it up during the day...

  7. #7
    Quote Originally Posted by hafa View Post
    Rough estimate:

    120V x .7A = 84W

    84W/12V = 7A (DC)

    7A X .1 (inverter consumption, estimated) = .7A

    total DC load = 7.7A

    1000AH/40 (max safe discharge for lead acid = 40&#37 = 400AH

    400AH/7.7A = 51 hours

    You could probably push it to 67hours/50% discharge, but that may be a bit rough on the battery.
    It makes more sense that the 0.7A is for 240V; for 100V(120?), the draw would be more of 1.4A.

    Which is now making things weird, since that would mean the laptop would draw more power than the inverter could provide (168W vs 100W)... I would assume your laptop battery would slowly die, and you would have to let it recharge with the laptop off.


    You could always just recharge the car battery with your car. And if you happen to have a 'deep cycle' or marine battery, you could theoretically drain it all the way.
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  8. #8
    Premium Member #24
    hafa's Avatar
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    Quote Originally Posted by neonblingbling View Post
    It makes more sense that the 0.7A is for 240V; for 100V(120?), the draw would be more of 1.4A.

    Which is now making things weird, since that would mean the laptop would draw more power than the inverter could provide (168W vs 100W)... I would assume your laptop battery would slowly die, and you would have to let it recharge with the laptop off.


    You could always just recharge the car battery with your car. And if you happen to have a 'deep cycle' or marine battery, you could theoretically drain it all the way.
    Thanks, neonbling, I grabbed the 240 value. If you were to apply a 168W load to a 100W inverter, the best case scenario would be that the breaker would cut out, at worst, there would be a bang and a puff of smoke.

    For an inverter that could handle it however, revised values:


    120V x 1.4A = 168W

    84W/12V = 14A (DC)

    14A X .1 (inverter consumption, estimated) = 1.4A

    total DC load = 15.4A

    1000AH/40 (max recommended discharge for lead acid = 40%) = 400AH

    400AH/15.4A = 25 hours

    You could discharge it further, but if you're planning on doing this frequently, it will adversely affect your battery's longevity.
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  9. #9
    Member Mr. Perfect's Avatar
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    168watts as imput for a 72watt output? 1.4A is probably at at 100volts. They spec it from 100-240, not 120-240. Well, that or it's only like 40% efficient.
    Last edited by Mr. Perfect; 11-13-08 at 08:34 PM.
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  10. #10
    Member Niku-Sama's Avatar
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    just buy a jumpbox.

    should have one any way if your camping for a long time, would suck to get stuck in the middle of no where.
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  11. #11
    How long can I run the laptop before the car battery discharges enough that I would have trouble starting the car??
    I'd think you would be able to prevent this problem by running the car for a couple minutes for every few hours. Thought it would use a little gas.
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  12. #12
    Member greyharte's Avatar
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    hhhmmmm interesting question and 25hrs is petty respectable ... and id certainly hope that you didnt spend your whole time camping sitting infront of your laptop

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