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Motherboard fan connections

Discussion in 'PC Hardware' started by Haines Brown, Mar 1, 2008.

  1. Haines Brown

    Haines Brown Guest

    I'm connecting an ENERMAX Liberty ELT400AWT ATX12V power supply to a
    GIGABYTE GA-P35-DS3L motherboard, and am uncertain about the fan

    The motherboard has four fan headers that provide 12V to fans:

    1. CPU fan header is no problem

    2. A 3-pin and a 4-pin Sys Fan header, one toward the rear of the
    board and the other toward the front. I presume that these supply fans
    mounted on the case. Since my old case fans plug into the usual 4-pin
    12V line from the power supply with its Molex connectors, I left these
    two headers unconnected.

    3. A three-pin Power Fan header, also located toward the front of the
    board. What is this "power fan"? If it is the fan in the power supply,
    why does it get its power from the motherboard rather than internally?
    Or is this a safety feature? My power supply manual describes this
    3-pin connector as "Fan RPM. For 12cm fan RPM detection", which sounds
    like it connects to something else, not a power source.
    Haines Brown, Mar 1, 2008
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  2. Haines Brown

    Arno Wagner Guest

    The "power fan" header is for monitoring only. It does not
    deliver 12V to the fan, this line is typically not even connected.
    But it reads the signal from the monitoring output of the fan in
    the PSU. Plug the fan cable from the PSU into the "power fan"
    header and you can monotor its speed, e.g. with SpeedFan.

    Arno Wagner, Mar 2, 2008
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  3. Haines Brown

    Haines Brown Guest

    Thanks, Arno,

    I re-read the motherboard manual, and see why it was easy to assume
    that each of the four headers it listed was a power header.
    Haines Brown, Mar 2, 2008
  4. Haines Brown

    gfretwell Guest

    The fan headers on most system boards are 3 pin. The center is ground,
    one side is 12v and the other side is the tach output for speed
    checking. Speed sensing fans have the matching connector. Non-speed
    sensing fans have a 2 pin, cinnect to the pair that works. It won't
    hurt to hook to the wrong side, the fan just won't run
    gfretwell, Mar 2, 2008
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