Controlling fan speed on a 3 pin motherboard?

[liamknox]

A friend bought a budget PC to get started and it was running hot because he only had 1 fan. I've made him buy more but the mobo only has 3 pin headers, fans are 4 pin, can I get something to control them via software or do I have to use the voltage limiters that came with the fans?

 

[why_wolf]

just plug them in. The fans will just fall back to 3pin mode (voltage control). You don't have to do anything special.

 

[photonboy]

just plug them in. The fans will just fall back to 3pin mode (voltage control). You don't have to do anything special.

WRONG. (AFAIK)
I've tested this though I'll admit there MAY be some fans that do work with 3-pin fan headers.

4-pin fans use PWM which is Pulse Width Modulation of a 12-volt source to control speed. It basically applies small pulses of voltage and the LONGER these occur the faster the fan spins.

3-pin motherboard headers work by varying the voltage between 5V and 12V with a constant voltage. You'll likely just have the 4-pin fans spin at one speed only with no way to modify this.

The voltage limiter usage MAY cause the fan to spin at a lower RPM but it's hard to say. There is circuitry in PWM fans so how they work with 3-pin + voltage limiter may differ between fans so it's possible the fans won't even start up. So either it's SLOWER or doesn't WORK but there should be no control capability.

Go ahead and try it though since if it's quiet enough it will do the job.

*Otherwise you need to get 3-pin fans (or just fans that use the 4-pin MOLEX and spin at a constant speed. You rarely benefit much from case fans above 800RPM anyway)

**4-pin fan headers are different. Most support 3-pin and 4-pin fans, though some do not support 3-pin. They transitioned to 4-pin and dropped 3-pin fan support but it causes such confusion they adopted support for both (AFAIK).

 

[JackNaylorPE]

You can use a 4 pin fan on a 3 pin header but it is NOT recommended. Yes, you will get speed control because lower volts but the fans won't have any of the advantages (i.e. low speed control) . may void thge warranty depending on manufacturer. I have not seen a MoBo w/ just 3 pin fans in 3 years. Most MoBo's today have 4 pin headers, auto sense the type of fan and will send a PWM or DCV signal as appropriate.

Even is you use PWM t modulate the voltage, it's a bad thing. Here's the language from Nidec... manufacturer of PWM fans including the revered Gentle Typhoons

Pulse-width modulation of DC operating voltage to modify fan speed [edit: in PWM devices] is not recommended. Transients generated by that approach can irreversibly damage motor commutation and control electronics and dramatically shorten the life of a fan.