How many case fans can one fan header drive/monitor?

Discussion in 'Asus' started by Percival P. Cassidy, Aug 21, 2013.

  1. I see 3-pin and 4-pin fan splitter cables advertised, but how many fans
    can a single drive header power and monitor without problems?

    The motherboard in this case is an Asus F1A75-V Pro -- if the specific
    board makes a difference.

    Percival P. Cassidy, Aug 21, 2013
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  2. Percival P. Cassidy

    Paul Guest

    Your manual contains no guidance on the subject.

    On my motherboard, it says:

    1) No more than 1.000 ampere from a single fan header.
    This would be a pin limit, for the tiny pins on the header.

    2) No more than 3.48 amps, from all four fan headers.
    That is a limit defined by the dimensions of the copper
    track distributing the +12V.

    The second line varies from one motherboard to another.
    It can be as low as 2.x amps on some motherboards. So
    if I had four fan headers, and I had to "guess", I'd limit
    myself to four 0.5 amp fans. Or two 1.0 amps fans.

    If you wish to power fans from a Molex 1x4, a Molex is probably
    good for 8 amps. It depends (slightly) on the wire gauge in
    the cable. The main connector (24 pin Molex) is 6 amps per pin,
    due to so many pins being adjacent. The 4 pin Molex is a bit
    better, at 8 to 10 amps, and we'll assume 8 amps.

    If you wish to power a fan off SATA, the 3x5 wafer power connector
    of SATA, is good for around 1 ampere per wafer contact. The three pins
    for +12V then, would have a 3 ampere limit. And this is much
    worse than when using a Molex for power distribution. Still,
    3 amperes will run a few fans, if you want. SATA power is a poor
    choice, for "daisy chained" cabling.

    I have one fan that draws an ampere, and I run that off a Molex
    rather than a fan header. Most other fans I've got, don't
    really challenge the above limits.

    Paul, Aug 22, 2013
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  3. Thanks for the reply.

    I meant "fan connector," of course, not "drive header."

    The manual says that the CPU Fan connector can supply 2A, but I found
    nothing about current ratings for the Power Fan and Chassis Fan connectors.

    Maybe I'll just stick with one fan per on-board connector and use "taps"
    into the drive power cables for the others.

    Percival P. Cassidy, Aug 22, 2013
  4. Percival P. Cassidy

    Paul Guest

    There are no fuses in the fan power path.

    If you overdo it, the track burns out. And there
    are some people who have suffered that fate. Hasn't
    happened to me yet, but not for lack of trying.

    At the very least, when playing around, don't plug
    in fans with the power on. In case you have an "off by one"
    event, or some other calamity like bending some pins until
    they touch one another.

    I've even had a computer crash, just by attempting to plug
    in a fan "hot". So... don't do that :)

    And if you have questions about a fan setup, by all means use
    the Molex solution. Fat wires, for the win...

    Paul, Aug 22, 2013
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