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Laptop 12V Pwr Supp efficiency

Discussion in 'Electronic Design' started by Leon Edddings, Apr 26, 2007.

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  1. I would like to run a standard notebook computer from a 12V deep cycle
    battery for mobile applications.

    In theory, which of the below is more efficient, given the same amp
    draw, about 2A average?

    1. A 12VDC to 120VAC inverter, in conjunction with the laptop's own
    external power supply that provides 18V.

    2. A 12VDC to 18VDC converter, and not use the laptop's supply.

    Thank you for any insight.

    Leon Eddings
  2. Number 2 (especially if it was a simple boost converter with
    no input output isolation) would normally be higher
    efficiency than the 120 to 18 volt supply. And using it
    eliminates one power conversion (the 120 to 18 volt supply),
    so that, alone, should produce 10 to 20% more efficiency.
    If the notebook will run on 12 volts, a direct connection
    (through just a fuse) would eliminate all external
    conversions and be most efficient.

    I am not responsible for any damage caused by the
    experimental test of this possibility.
  3. Eeyore

    Eeyore Guest


    Every time.

  4. Bob

    Bob Guest

    I used three 6V lead acid batterys in series to run a laptop. Why not
    just start with the right voltage?

    When I tested it with a variable psu the old laptop I had worked down
    to about 10.5v. It drew more current than running at 18V. It normally
    used about 40% of the rated power of the mains psu so it would
    probably have been fine on 12V without the sound , USB, and CDROM
    using power.Other models may vary.

  5. Phil Hobbs

    Phil Hobbs Guest

    Another consideration is the health of the laptop. It has its own
    switching power supplies inside, which present a pretty weird load to
    the external supply. Laptop bricks handle this well, but cheap 'n'
    nasty switchers might not, and it's quite hard to test for without
    putting the computer at risk. If you're using an expendable laptop, go
    for the gusto, but if it's your pride and joy, stick with an AC inverter
    and the normal laptop power brick.


    Phil Hobbs
  6. ehsjr

    ehsjr Guest

    I agree. Not having to buy a new laptop is the most efficient.
    I wouldn't even trust an AC inverter where "an" means any
    old POS inverter. I vote for 18V DC from batteries. Charge
    them with any old POS inverter and a good charging circuit.

    The OP did ask stipulating "in theory" and got good answers to
    that question.

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