Circuit to simulate a computer cooling fan?

[tongro]

I have a server computer which contains three cooling fans. The fans' speed is controlled by firmware, but even the lowest speed is very loud, even though all the internal components are always very cool to the touch.

So, I want to find some way to reduce the noise level. When I removed one of the fans, the machine's BIOS objected loudly, refusing to boot. So then I took a spare fan and hacked off the rotor housing and connected it, but this seemed to screw up the feedback signal, and the fan's "failed" light came on and the BIOS objected again. Another option would be to simply cut off the rotor blades, but they are very difficult to get at with ordinary tools.

The next thing I would like to try is to construct a simple circuit which would simulate the presence of a fan. There are three connections; 0V, supply (presumably variable voltage), and feedback. I'm not an electronics engineer, but I do have some experience of amateur electronics and can build a simple circuit from a schematic.

So, can anybody point me in the direction of a suitable circuit or discussion of the technology involved, or provide helpful hints of any description?

Thanks very much.

Tony.

 

[monkeysolder]

I've got an idea -

Tap the signal line coming off of one of the other fans and run that signal to the connector of the fan you want to remove.

 

[monkeysolder]

Err, "run that signal to the connector on the motherboard of the fan you want to remove", I mean.

 

[tongro]

Yes, tapping the feedback signal sounds like a great, easy, safe idea; I'll try that. But before I start, does anybody know offhand which is the feedback wire - red, black, or yellow?

 

[LionelHutz]

I don't understand why reducing the voltage with a resistor or pot won't work. The motherboard bios should have settings for the allowed fan speed and even for turning fans monitoring off. At the least, I'd think it has to allow for a slower speed fan to be installed, since you can get fans that operate from about 1500rpm to 6000rpm.

You can purchase fans with a built-in or externally wired potentiometer specifically designed to allow the fan speed to be adjusted. They still provide a feedback signal to the motherboard.

You can also buy fans with temperature sensors that will adjust speed depending on the temperature sensed.

 

[ko99]

Tongro, usually red is positive, black is negative, and whatever's left is the tach signal.

ko (

http://www.ecooling.biz)

 

[itsmoked]

Which is confusing because yellow is the +12V in PC's and RED is the +5V. But ko99 is absolutely correct.