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View Full Version : Couple of questions on cooling fan wiring



Bucko
01-31-2007, 11:02 AM
I bought some nice looking blue cooling fans for my PC, but I'm not 100% sure on what all the wires are for.
They have the three pin plug on them like a CPU fan does, but I'm not sure what the yellow wire is for.
I know the black and red are the 12v positive and negative wires, as the fans came with a 3 to 4 pin adapter and the red and black go to the 12v power, but coming off the adapter is the back wire and the yellow wire going to another plug the same as the fan.

Here's a couple of pics to make it easier to explain (excuse blurriness, my cheap camera doesn't like close ups):

http://img253.imageshack.us/img253/8199/plug1bo6.jpg

On the right is the three wire fan plug, on the left is the adapter lead that came with it. The adapter lead has 4 wires coming out, red, two black from the same socket, and the yellow.
So as mentioned, the red and one black go to the 12v half of a 4 pin molex, but the yellow and other black goes to this:

http://img529.imageshack.us/img529/1395/plug2hh6.jpg

It's the same plug as on the end of the fan lead, however it only has the 2 wires, ie no red 12v + wire. So there is the spare pin in the plug.

Now these fans came with no instructions, so I can't RTFM either.


And finally on these fans, they have a small variable resistor coming off them to adjust the speed, which looks like this:

http://img61.imageshack.us/img61/5622/speedadjustvt5.jpg

It is adjusted with a small phillips head and only has two wires going to it and says 20k on the side.
My question is, if I want to control the speed of both fans at once, rather than 2 speed controls, I want to put one bigger (in size, not value) varible resistor on the front of the case. What would I need to do as far as wiring goes?
I know it should be a simple job, but I'm having a blank.

Thanks in advance.

Lee.

SgtM
01-31-2007, 11:37 AM
Unless I'm mistaken, the 3rd wire is for monitoring the fan's RPM's. As far as wiring, I think if you put it in parallel, you should be ok with the (1) 20k variable resistor.

xmastree
01-31-2007, 11:38 AM
The third wire is the speed sensor, for feedback to the motherboard. (ever wondered how it knows how fast the fans are running?)

You can safely disregard it.

Bucko
01-31-2007, 11:47 AM
Thanks!

On the fans that I may not need the speed control on, would just bypassing the resistor by joining the two wires make the fan run at full speed?

slytherock
01-31-2007, 11:47 AM
They are both right about the third wire. The 3 of them are explained here (http://www.thebestcasescenario.com/forum/showthread.php?t=6044)

edit: and for your last question: Yes. It will run at full speed (12V)

Bucko
01-31-2007, 11:59 AM
Thanks all!

It cleared up what I thought, but just wanted to confirm.
Now I can make some plans about wire management for the fans.