p4 and psu amperage

Discussion in 'Asus' started by Guest, Feb 5, 2004.

  1. Guest

    Guest Guest

    what would be the minimum amperage on the 12 volt line for a p4 on a
    Guest, Feb 5, 2004
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  2. Approx. 15 A on a good quality 300W PSU. (At least that's about the
    minimum I'd use.)

    Stephan Grossklass, Feb 5, 2004
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  3. Guest

    DaveW Guest

    Which P4 did you have in mind?
    DaveW, Feb 6, 2004
  4. Guest

    Paul Guest

    You can do a rough estimate for yourself.

    Download a datasheet for the P4 processor you are interested in.
    There should be a design max current consumption number in the datasheet
    and that is where you start.

    Imax * 1.5/12 * 1/0.80 = I for Vcore circuit coming from +12V supply.

    This equation is just the ratio of Vcore to the supply voltage and
    the second term is correcting for the 80% efficiency of the Vcore
    circuit. For example, a 3.06Ghz/533 P4 draws 52.5 amps from Vcore, and
    this would be 8.2 amps from +12V. One of the new Prescotts would be
    quite a bit more.

    For disk drives, during spinup they draw 2A from +12V. When the spindle
    is finished spinning up, the drive will draw about 0.5A. Most
    manufacturers have data on this, so you can use your own, real numbers.
    Note that during spinup, the processor may not be running flat out,
    so it would be pessimistic to take max for the processor and max
    for the disk drives at the same time.

    Current to run the CPU and case fans is frequently printed on the fan
    itself. If it isn't, estimate 1 amp to run all of them.

    High end video cards have a drive power connector, and the highest
    consumption I know of, is the FX5900 at about 70W or so. A
    pessimistic estimate then, would be to include [email protected] to run a card like
    this. Cards without the drive power connector, draw their power from
    +5 or +3.3, so those video cards don't enter into the calculation
    of +12V consumption.

    As Stephan says, for a small install, 15A should cover it. If you
    have a high end video card, or a lot of disk drives, you might want
    to look at the calculation in more detail.

    Paul, Feb 6, 2004
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