# FreeBSD 8.2 CPU fan speed control



## soulreaver1 (Nov 24, 2011)

Hello,

I've a problem with cpu fan speed control. It seems that FreeBSD doesn't know how to control it. Fan is always running at 3000 rpms, even if the core temp. is lower than 20 celcius. CPU is underclocking Sempron 3000+, mobo is Asus A8V-VM SE. Is there any way to limit a speed of fan in FreeBSD?

Ps. powerd is enabled.


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## User23 (Nov 24, 2011)

Hi,

is "Cool â€˜nâ€™ Quiet" enabled in the BIOS? (Handbook ASUS A8V-VM SE: 2-25)

Btw. normally the BIOS is controlling the CPU fan speed.


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## soulreaver1 (Nov 24, 2011)

Yes ,"Cool â€˜nâ€™ Quiet" is enabled. Interesting that on mobo there is only 3-pin cpu fan socket. Cpu fan has tree wires (black - ground, red - positive, yellow - rpm reading). There is no pwm-control wire, so it looks like it's impossible to control fan rpms. 
Anyway, i shall limit it manually, by putting a resistor (or better thermistor) into fan circuit. But I'm still curious whether controlling of fan rpms using 3-wire is possible or not?


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## mroussin51 (Jan 27, 2012)

*Of course a fan be controlled in open loop*

It is less accurate though.


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## mroussin51 (Jan 27, 2012)

*I have proved myself wrong*

I checked out some 3wire fans against some 4wires fans and found that the 3wire fans all were set to WFO. I always thought that the voltage was being controlled. I built a temperature controller for a large barbeque grill using a homemade thermal couple, a PID controller, a transistor, and a baffle fan. I thought the mobo could do the same analog voltage output to the fans as I did with a loop controller. I was wrong. I am going to get back to being a junior member again!


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