2-Wire, 3-Wire & 4-Wire Fans

[Golodkin]

I'm confused about CPU and system fans interfacing with MB speed controls.

Of course, 2-wire fans are one-speed...but why do CPU fans have both 3- and 4-wire connections?

I was under the impression that 3-wire fans could be speed-controlled by the system BIOS to respond to increases in CPU/system temperatures as reported by the sensors. For testing while I wait for a good deal on a newer/faster CPU I am temporarily using a 3-wire CoolerMaster heatpipe-tower CPU cooler in a recent build (not on the system in my sig) with an AMD Phenom II 720 from another older box.

The CPU cooler seems to be working with the fan at full (?) speed (an indicated ~1900RPM), and the CPU as a consequence just barely makes it past ambient temperature at sustained 100% load. In the BIOS I have fan speed control turned on, which I believe is default.

So, what's with this? Shouldn't this fan be barely spinning? Am I wrong and ~1900RPM is relatively low-speed and this is just the lowest available speed increment? Is variable fan speed unsupported by this older CPU? What?

Why do some of my newer CPU coolers have FOUR wires going to the CPU Fan plug?

Many thanks for any clarification!

 

[Railgun]

2 wire fans are just fans with no RPM signal. You can still control them via voltage.

Most current mobo fan headers are only PWM controlled (4-pin) so that would explain what you see. Some can be manually controlled by duty % but IIRC that may also be PWM. Check your mobo manual.

 

[ehume]

2 wires: Gnd/12v. Variable control of Voltages controls fan speed
3 wires: Gnd/12v/RPM. Same + reports its RPM to the motherboard.
4 wires: Gnd/12v/RPM/5vPWM. Same as above + 4th wire carries the motherboard PWM signal to the fan, controlling its speed.

 

[Golodkin]

OK, good, now I get it. ONLY 4-wire fans respond to control from the MB. It appears I was misinformed some years ago. It never came up with my recent build in the sig because the 950 is speed-controlled by some elaborate rigmarole involving USB and software.

Is there a simple practical way of reducing the fan speed of this heat pipe cooler?

Of course, the obvious answer is to overclock the CPU hard enough to make the fixed fan speed relevant to the application.

 

[tachi1247]

The only way to reduce the fan speed on your old cooler would be if you're mobo supports voltage control. If it fits you could use software provides either by the board manuf or a third party to adjust it's speed. That assumes the fan supports different speeds. It's possible that when you reduce the voltage the fan will just shut off.

 

[Conumdrum]

Disconnect the 950 cooler from the CPU header. Connect the supported fan on your standard Air cooler that has heatpies (3 or 4 wire depending on the mobo) to the CPU header on the mobo and use the mobo software or bios to adjust the trigger points for speed to change.