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CPU Fan Speed. — Parallax Forums

CPU Fan Speed.

PLJackPLJack Posts: 398
edited 2005-11-04 22:26 in General Discussion
Anyone know how the speed of a CPU fan is measured.

Is the fan reporting its speed or is it extrapolated from the electrical nuances?

I need to make a test rig for testing fans. I’m thinking a black box with a SX chip powering each fan on one at a time and measuring the RPMs.

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- - - PLJack - - -


Perfection in design is not achieved when there is nothing left to add.
It is achieved when there is nothing left to take away.

Comments

  • stamptrolstamptrol Posts: 1,731
    edited 2005-11-04 14:59
    Many of the newer fans have a tachometer signal built into the unit. It can be either a pulse stream or analog voltage.

    With an external controller, the controller senses the temperature of the cpu and adjusts the fan speed up and down, using the tach signal as feedback.

    On fans designed to operate over wide voltage ranges, an on-board controller senses the fan speed and holds it constant regardlees of the input voltage.

    Tom
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-11-04 15:08
    Recently my PC was flashing a warning. First the 3.3v supply was low, then the chassis fan was indicating low.

    So I pulled all apart and cleaned the interior. The voltage corrected, but the fan did not. It seems that not all CPU fans are alike. Some have three wires and some have two. The ones I have with the speed indicator in software are three wire fans. That third wire appears to be needed either as a speed control or speed indicator or both.

    Incidently, I replaced the fan and the new one didn't function properly either [noparse][[/noparse]early shutdown]. The manufactor included an addapter to use two wires of the 12volts from a floppy driver power. I used the adapter and now the fan runs 24/7. So, with only two wires in use, the mode is full on.

    I couldn't locate a schematic of the fan and the resistance measured open on all three leads in the new and the old fan.

    You can get the diagonstic software from ASUS [noparse][[/noparse]ASUS Probe V2.15] and try to reverse engineer what the are doing. They don't seem to provide a schematic of the motherboard.

    If you can figure out that third wire, you have your answer.· Try putting a scope on it.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • PLJackPLJack Posts: 398
    edited 2005-11-04 22:26
    Thanks for the ideas, gang.

    I always assumed the third wire was a 12v feed. That way the fan could run on 5v for low speed or 12v for high speed.
    I will put a scope on the third wire and let you all know what I find.

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    - - - PLJack - - -


    Perfection in design is not achieved when there is nothing left to add.
    It is achieved when there is nothing left to take away.
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