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Why do some pc fans have 3 wires and some don't?

Discussion in 'Hardware' started by superstar, May 26, 2009.

  1. superstar

    superstar Command Sergeant Major

    Why do some pc fans have 3 wires [ie: red, black, and yellow], and some pc fans just have two [ie: red, and black]. A friend of mine told me that the yellow wire does nothing... Is this true? I want to take the white plug off a 3 wire fan and put the wires on a white 2 wire plug.
  2. studiot

    studiot MajorGeek

    All fans have 2 power wires - DC ones have + and -.

    Without these they will not run.

    With just 2 wires they either run or they don't ie the speed is constant.

    More modern fans also have built in speed sensors. The signal from this is fed down the third wire to control circuitry on the motherboard which reports the speed the fan is running at to the BIOS and programs like speedfan.

    A modern BIOS can exert conrol over this speed by varying the supplied voltage. Some programs can also do this (but not Windows itself).

    Its a bit like the electric fan in your automobile.

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