Adding a 2nd front fan to the cpu case

Posted on 2009-02-10
Last Modified: 2013-11-10
The problem is that my motherboard have only 1 connection with RPM control in front, and the extra fan have the yellow cable available... so my idea is this: can i weld the yellow cable of the extra fan to the yellow cable of the existing fan?? obviously the oders black and red cables will be attached to the power supply with a generic connector
Question by:Flotron
    LVL 4

    Expert Comment

    Yes you can...however the way it works out RPM is through resistance over the wire, and therefore doing this will double the resistance (ie Fan controls, readings etc) will be halved.

    If you want to do this just to reduce FAN noise by running it slowly, you can buy very cheap ($5) kits that have a twist knob to control fan speed.
    LVL 91

    Expert Comment

    LVL 26

    Accepted Solution

    If you have 3 fan wires the third wire is not a 'control' it's a 'monitor'.
    It's an RPM -SENSOR-, not a speed control.

    What it senses is 'read' by an IC chip on the motherboard and the +12v power to the fan is adjusted to control the fan speed. (It may be adjusted either on the +12v or ground side of the fan header. That depends on the specific controller design.) That IC chip usually also has an input from a temperature sensor and it uses both inputs to set the fans speed.

    You should -NOT- splice RPM sensors together or the IC chip will 'be confused' set the fans to the wrong speed.

    You could splice the power and ground wires wires from a motherboard header to a second fan and NOT splice the sensor wire,,, that would cause both fans speed to be controlled based on the RPM of one fan which should be okay.

    4 wire fans are the same as far as those 3 wires.
    Do NOT splice sensor wires.
    In 4 wire set-ups the 4th wire is a control (not just a sensor) and the 4th wire could be spliced.

    One other caution.
    Motherboard fan headers have current limits. It's usually not much.
    Two fans to one header may exceed that limit and burn out the fan controller IC chip completely.

    LVL 91

    Expert Comment

    that was what i suggested - see above

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