thermal control conflic?: Intel retail fans and motherboards

dnewhous · Post by **dnewhous** » Tue May 03, 2005 3:55 pm

I have just read, in a review article here, that Intel 775 pin CPUs come with thermally controlled fans. First off, if the fan is self-controlled why'd they bother with a 4th control wire to the motherboard? Second, and more pressing, if you intend to buy a motherboard with its own thermal control for the CPU fan, the choices are either buy a different CPU fan or turn off the motherboard's thermal control, are they not?

tay · Post by **tay** » Tue May 03, 2005 4:58 pm

The 4th pin is the pwm pin. Search the forums for 4 pin PWM fan. Its been discussed by people more knowledgeable than I am. And a little bit of searching yielded this post by StarfishChris :

You're referring to a PWM fan, which is similar to the 3 pin fans except for that fourth control wire. Ordinary 3 pin fans are controlled by pulses of 12v which can stop fan circuitry working as intended and/or cause the 'grumbling' sounds in some fans. The 4 pin fan maintains constant 12v but has the fan control itself by getting input from the fourth control wire. Of course this depends on a motherboard supporting that...

Further searches will reveal where to buy them (JMC for eg.).

Use the search Luke!

dnewhous · Post by **dnewhous** » Tue May 03, 2005 5:36 pm

Yes, I started that thread. The second question above is the more important one.

tay · Post by **tay** » Tue May 03, 2005 5:44 pm

Well the second question doesnt make any sense to me.

dnewhous · Post by **dnewhous** » Tue May 03, 2005 6:04 pm

There is an important implication here. A motherboard that wants to thermally control a fan and a fan that is self thermally controlled constitutes an unacceptable conflict. Thus, the second question.

It is possible that the Intel fans come with a switch (though I have never heard of such a feature) that turns off their thermal control.

I have checked, and ASUS 775 pin mobos let you enable/disable the thermal control on the CPU fan and case fan separately.

tay · Post by **tay** » Tue May 03, 2005 6:16 pm

I dont believe that there is a conflict. Fans that have attached controls are generally either controlled by a thermistor or a variable resistor. And these fans work just fine with added PWM control (the 3pin variety is the only ones I've used).

The 4th pin is sending signals telling the fan its duty cycle. If its the intel retail 4 pin fan it will rely on this signal to control itself. No signal = no control and 100% speed. If its a 3 pin fan I think you'll need external control. I'm afraid I'm not understanding what youre still asking.

dnewhous · Post by **dnewhous** » Tue May 03, 2005 6:43 pm

When the stock Intel CPU fan was described as having thermal control, I took that to mean the fan speed would be variable even if it were merely connected to a 2-pin power connector. Maybe I misunderstood and it was just a reference to thermal control being a standard feature on motherboards.

tay · Post by **tay** » Tue May 03, 2005 6:44 pm

Yeah I would assume that to be the case.

dnewhous · Post by **dnewhous** » Tue May 03, 2005 8:23 pm

Yes, the offending line is " Intel's stock P4 coolers use thermal fan speed control."

The correct statement is "Intel's 775 pin P4 motherboards use thermal fan speed control."

Big difference. cooler = heat sink + fan assembly when the term is used properly.

Tibors · Post by **Tibors** » Wed May 04, 2005 12:24 am

I think it would have helped in getting an answer if you told in which review, which page and which paragraph you read the phrase you are questioning about. Then people can go and read the context and maybe better understand what the prooblem might be.