3-wire CPU fan RPM signal specs

[Bert]

Hi

does anybody have any idea what the specification is for the RPM signal on a 3-wire CPU fan?

Google was of no help, the major motherboard manufacturer's sites weren't, neither were sites of the likes of cooler master etc. And it wasn't even on epanorama.net.

I am trying to reduce PC noise by attaching a bigger fan at lower RPM, but I need to know how to generate the RPM signal or the motherboard's low level monitoring systems will raise the alarm.

I rather see the specs laid out somewhere instead of reverse-engineering it with a scope.

Thanks in advance!

Bert

[Tomi Engdahl]

There are at least two types of signals that can be transported through this third wire depending on the application:

Many fan applications require circuits that monitor operation and provide an output (alarm, shutdown) on a third lead wire if the fan's speed falls below an allowable minimum.

Another option available option is tachometer pulse output. The signal lead of the fan is most often internally connected to the collector of a transistor that is triggered by the commutation of the motor windings. So this circuit provides a known number of pulses per revolution. For example some Nidec fans provides two square wave pulses per revolution. I don't know if this is fixed number or can this vary between different fan brands. I quess that the PC fans where the motherboard knows their rotation speed use this tachometer signal.


Here is some more information on this topic:

How to make RPM Signal for 2-Wires Fan
http://forums.silentpcreview.com/viewtopic.php?t=3565

[Bert]

This was the link I was looking for!

I wonder why I wasn't able to find it.

Thanks a lot!

Bert

[0skar]

I stumbled onto this site. There's some information on 3 wire cooling fan tachometer signal standards here:

http://www.petervis.co.cc/cpu%20fan%20t ... tacho.html

hope it helps.

[Tomi Engdahl]

Nice resource.

[John Patell]

Hello,

I am new to writing on forums, so please forgive me if I make mistakes.

I just wanted to say thank you for your outstanding forum. I spent hours trying to find info on Tachometer Signal Standards, this forum is the only place on the whole internet where this information can be found. Truly Excellent.

Oh, by the way the link above has changed address, I managed to find the information at:

http://www.petervis.com/electronics%20g ... tacho.html

thank you once again very much

JP