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Re: [Electronics_101] calculating amp draw of inverter

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  • Andy
    ... Sorry, no. The amperage ON THE 120 V SIDE will indeed be 8.3 A, if the load is resistive. But you wanted to know the current on the 12 V side. The
    Message 1 of 3 , May 7 9:24 PM
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      > If I have an inverter that providers 1000W @ 120V from a standard automotive
      > 12VDC (13.8VDC) system. Can I calculate the amp draw by doing 1000/120= 8.3A
      > to see how much of a drain this device will place on the auto system?

      Sorry, no.

      The amperage ON THE 120 V SIDE will indeed be 8.3 A, if the load is
      resistive. But you wanted to know the current on the 12 V side. The
      inverter acts like a transformer. Voltage transforms one way; current
      transforms the other way.

      1000W out means something greater (in watts) into the inverter. For
      purposes of this exercise, let's say the inverter is 90% efficient at
      this power level, meaning it draws 1111 watts from the 12V side. The
      excess 111 watts goes into heating the inverter.

      1111 W / 13.8 V = 80.5 Amps, drawn from the car's electrical system.

      If the DC voltage drops, say to 12.0 V, then the current increases to
      92.6 A to deliver the same power.

      If the inverter's efficiency is less than 90%, the required input
      wattage, and amperage, must be greater.

      Regards,
      Andy
    • lists
      In article , ... And at those kind of current levels the internal resistance of the battery
      Message 2 of 3 , May 9 1:35 AM
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        In article
        <CAN_saPLOC0uOd8ibqOTob7wKGG=L7-pUqxR_tqP1sn6Wg2irvg@...>,
        Andy <ai.egrps@...> wrote:
        > If the DC voltage drops, say to 12.0 V, then the current increases to
        > 92.6 A to deliver the same power.

        And at those kind of current levels the internal resistance of the battery
        will indeed cause the output voltage to drop - by quite a lot.

        --
        Stuart Winsor

        Midlands RISC OS and Raspberry pi show, 13th July 2013

        http://www.mug.riscos.org/show13/MUGshow.html
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