hey all,
building a new comp this december (hopefully if my 'rents dont make me "help" them buy me a new car ) and i was looking into a fan controller among other things and was checking out the pin-outs for a 3-pin fan controller (+12V, ground, RPM signal... in no specific order). I know what the signals look like for +12V DC and ground.. thats pretty simple.. but what is the signal for the RPM pin? One webiste say that its a 'sense' as if the MB is detecting the RPMs but another website says that its a signal as if the MB is outputting something.

what's the story? is the MB, or other controlling device, outputting a signal? and if so what does that signal look like?

thx

Here are the pin outs at least...

Pin 1 is GND
Pin 2 is 12+
Pin 3 is Sense

Even though I may build and customize computers, I don't go that detailed into a simple fan connector, lol. If it's 3-pin, I make sure to get a 3-pin fan or whatever I'm looking for. Though, as far as I know, the sensor is usually on the motherboard.

k, thx for the feedback.

i was just wondering if the MB put out some signal or exactly how that third pin controls the RPMs of the fan.. just curious i guess


P.S. yes, i am an engineer...

The third pin has momentary contact at one point for use as a timing signal.
This outputs the rpm's to the input device which controlls the supply voltage of the fan.
Pin 2 normally outputs between 4.3v - 12v on current systems.

ATX power supplies are another good example of 3pin fan configurations.
These are controlled by a heat sensor, more heat=more voltage=faster rpm's.
Turn it on cold & the fan barely runs, overheat it & the fan "screams".

There are fans on the market that are self-controlling based on heat, but they only have a 2pin configuration.

Hope this helps.

P.S. no, i am not an engineer...

Ahhh, so the 3rd pin is a signal from the fan (?) that allows the controlling device (MB, fan controller) to regulate the voltage of the fan, much like a rheostat, correct?


thx for the clearification

Whats a rheostat?

Yeh, thats pretty much the same.
It's more like a optical timing mark used to calibrate machinery.

hmm, interesting.. thx hilander