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How long can you run a 90W power supply off the battery?

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  • How long can you run a 90W power supply off the battery?

    Hi all,

    A question to all the electricians out there - supposing a power supply was drawing the full 90W it is rated for, how long could you theoretically run it off an average car battery before it went to critical and left the car unable to start?

    Cheers,

    -pN
    Doko ni datte, hito wa tsunagatte iru...

    My BMW 335xi install
    My Subaru Impreza install (now retired...)
    Realtime audio freestyle hiphop battles online - www.letsbeef.com!

  • #2
    90W/12v= 7.5A... then you'd need to know the voltage discharge characteristics of the particular battery in question, which usually are far from linear. and you also need to know the voltage at which your car can no longer start.

    in other words, it's probably better to get an answer by testing it out, than by trying to calculate things.
    But don't take it from me! here's a quote from a real, live newbie:
    Originally posted by Viscouse
    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
    eegeek.net

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    • #3
      I was thinking I should at least try to get a ballpark idea so that I don't wind up with a dead car in the middle of the forest if I decide to use the computer for an hour or so. All right - how about I phrase it this way: what's the average people have gotten?
      Doko ni datte, hito wa tsunagatte iru...

      My BMW 335xi install
      My Subaru Impreza install (now retired...)
      Realtime audio freestyle hiphop battles online - www.letsbeef.com!

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      • #4
        Originally posted by Pseudo Nim
        I was thinking I should at least try to get a ballpark idea so that I don't wind up with a dead car in the middle of the forest if I decide to use the computer for an hour or so. All right - how about I phrase it this way: what's the average people have gotten?

        I have a feeling few people have actually tested it. Also, how are they supposed to know at exactly what momen the car became "unstartable"

        Let me throw a number out at you, an Hour. Now, don't come crying to me if you get stuck in the forest after 55 minutes. There is no way to know how long it will last.

        Also, your battery could be "old" and not maintain a charge as well as someone with a the exact same battery, but new. That means that the amount of time can change, even for the exact same battery, in the exact same car. Oh, and perhaps if you don't drive the car far enough to fully charge the battery, it will be even shorter.

        So, short answer, no one can tell you the answer to your question with any certainty.

        Michael
        ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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        • #5
          i did a 90watt opus on my friends magnum and i used it for about 10 minutes total just booting and shutting down without starting hte car and the next morning i had to give it a jump stock magnum battery btw but on mine with a 300/600 watt inverter and a 90 watt power supply i can run it for a bout 2 hours almost and still have a clean crank

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          • #6
            my battery lasts an hour with 2 amps on (very low) and an opus 150w, after that hour i cant start the car
            Signature: [==||========] 20% complete

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            • #7
              Don't forget to compensate for temperature also. A battery's optimum temp is 80 degrees and it's capacity to store energy drops as it gets colder but it's life is longer, hotter will give you more capacity, but is detrimental on life... Also, a battery is said to be fully discharged at 10.5 volts, and dropping a lead acid battery to that point a few times will ruin it pretty quick (starter batteries because of their thin plates anyway, deep cycles can handle it much better because of the thicker plates, but is still not good) I never let my batts drop below 11 volts.

              If you're going to test, be sure to keep a volt meter on it, preferrably one with 2 decimal points, but one is ok. Dont let your batt drop too low or you risk damaging it and it might not last 10 minutes after that.

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              • #8
                Use a PSU with low voltage protection so it shuts down the PC before the car becomes unstartable (Opus, Carnetix, M1ATX...)
                Originally posted by ghettocruzer
                I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                Want to:
                -Find out about the new iBug iPad install?
                -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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                • #9
                  it also depends on how many watts youre actually using. a 90W PSU doesnt always consume 90W..

                  I have left my carputer on for 3-4 hours (no amps/stereo) and my truck started right up and didnt even reset the computer.
                  G945GLCF2 | 512MB RAM | 160GB HD | Holux GPS w/ Routis | XMPCR w/ TOSLINK mod | Audigy 2 NX | | Xenarc 700TSV |Opus 150W PSU.

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