Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Creating a fan control via a Potentiometer

  1. May 30, 2011 #1
    Hi, I wanted to create my own computer fan control and bought a 100ohm potentiometer.

    I have hooked the pot as shown in the picture except that it is in the yellow wire (+12V) and not the red one (+5V) , black is ground.


    The fan will start at full speed and doesn't change one bit if I turn the knob. Any ideas why the pot doesn't work?
  2. jcsd
  3. May 30, 2011 #2


    User Avatar
    Gold Member

    Just for clarification, does the attached circuit accurately represent what you have done? i.e. you're essentially trying to create a voltage divider with only one resistance (assuming the load resistance is << the potentiometer).

    Attached Files:

  4. May 31, 2011 #3


    User Avatar
    Science Advisor

    If this is a standard computer fan, the red wire is probably 12V (or sometimes 5V), black is ground, and yellow is the tachometer OUTPUT from the fan. HOWEVER, the colours are not standardized across all manufacturers (though the functions will be--the fan label usually tells you which is which).

    Can you hook up a multimeter to the leads you've connected, and see if the resistance is actually changing when you turn it?

    EDIT: What I meant to say with the colour coding is that you've left it somewhat ambiguous as to which red and which yellow wires you're using: the fan's or the power supply's.
  5. May 31, 2011 #4
    The POT is currently attached to the yellow wire as Zryn's picture shows. And the other wires are unchanged. My PSU has a color label saying yellow (+12V) black (ground), another black (ground) and a red (+5V) .
    But I think you are right about the color coding of the 3-pin fan wires, red is +12V, yellow is monitor (RPM) and black is ground.

    I will try putting the POT on the red one and see if it fixes it. Seeing the color label on the PSU just confused me a bit + I'm not that good with electronics.

    Added 6.12 PM
    Works like a charm, thanks for the help!
    Last edited: May 31, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook