Subject: yellow cooling fan connection
By: Lou Bricant (IP: 87.242.153.*)
Written on: 29-01-2007 17:36

I have observed that most cooling fans have 3 wires red black and yellow. The red and black can go to the cooling fan 3 pin connector, or to the 12 volt connections on what I will call a 4 pin hard drive connector, connecting to the yellow and black connections to give 12 volts.
The 3 pin connector has an additional lead , a yellow wire, this comes from a temperature controller on the chip I think and is to slow the fan down when the chip is cool.
What I am asking is this ....How does this speed control work? Is the yellow wire supplied with a variable voltage to control the speed? Alternatively I wondered if the speed might be controlled by a variable resistance onto the yellow wire , as the resistance to earth changes, the speed would change. I guess its probably one way or the other. Any advice or knowledge gratefully received

By: Lou Bricant (IP: 87.242.153.*)
Written on: 29-01-2007 17:53

OK guys, I found out the yellow wire is a speed sensor wire, which reports fan speed back to the CPU , fan speed is varied by chnging the volyage on the red and black , just like in the good old days!
Thanks anyway
Lou Bricant
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