RPM sensing on 2 wire fans

[Rugger]

Alright, I've got a bunch of Sunon fans that have 2 wires coming out of them. Is there any way I can open up the fan and possibly solder on the third wire somewhere and sense the RPM's via my mobo. Or do they build 2 wire fans without the rpm sensing?

[Silversinksam]

Pull back the sticker on the fan to see if it has a third area where the third rpm wire may be soldered too.

If so heres a few sites to get a few ideas on what to

http://www.overclockers.com.au/techstuff/a_fansplit/

[Rugger]

Thanks for the info. The 80mm and the 90mm's peel back to reveal a third solderable connection which I will assume is the rpm monitor. I've got 2 120mm's that don't allow the sticker to peel back. Is there any way to get inside the fan without destroying it? (I'm betting it has space for a sensor wire if I can find it).

[flounder43]

Well, by my count, you are running out of fan headers to do the monitoring anyway...

I have two 120's and I don't even know what the rpms mean with those big fans...

[UnaClocker]

Well there's always the digidoc5, which can monitor 8 fans, toss in a good motherboard with 4 headers, even a deaf aircooling nut would be hard pressed to have more than 12 fans. :)

[flounder43]

Originally posted by UnaClocker
Well there's always the digidoc5, which can monitor 8 fans, toss in a good motherboard with 4 headers, even a deaf aircooling nut would be hard pressed to have more than 12 fans. :)

You are correct, sir. I wasn't thinking just then...

[UnaClocker]

Oh, another thing I just thought of. Alot of fans have something called a "locked rotor sensor" rather than a hall effect pickup for RPM monitor. All the locked rotor sensor does is tell if the fan isn't spinning, and it requires a special circuit to read that. (I've seen the wiring diagram for that somewhere, just didn't care to bookmark it).. So if you solder on the wire and don't get any RPM monitoring, you know what kind of sensing your fan probably has.. :)