3-Pin and 4-Pin Motherboard Fan Headers

Jason W · Post by **Jason W** » Fri Aug 17, 2007 8:37 am

My Gigabyte GA-P35-DS4R motherboard has 4 fan headers:

CPU_FAN - 4 Pin
PWR_FAN - 3 Pin
SYS_FAN1 - 3 Pin
SYS_FAN2 - 4 Pin

First question... are both of the 4 pin headers PWM headers? I am assuming the CPU_FAN one is since it's meant for the CPU heatsink fan, but I'm not sure about the SYS_FAN2 header. The motherboard manual doesn't give any details about this that I can find.

Also, I have 4 orange Nexus 120mm fans, and I do not believe any of them have the 4 pin connector. All I remember seeing is a single 3 pin connector, and then 2 molex power connectors on each one.

Is there a way I can still connect these Nexus fans to the CPU_FAN or SYS_FAN2 headers? Does someone make a 3 pin to 4 pin converter?

Thanks!

FlorisNielssen · Post by **FlorisNielssen** » Fri Aug 17, 2007 10:33 am

First answer: Those 4pin connectors both are for PWM fans.

Second answer: I'm not sure with your Gigabyte motherboard., but often you can put a 3pin connector in a 4pin header. It'll certainly fit, and often works too.
Nexus fans don't have a 4pin connector, you've seen that right. You should just try to connect them and see what happens. Worst case scenario is probably that your Nexus will be running at 12V. I don't know if you can get it any lower with Speedfan or something. Maybe you do need a PWM-fan for that.

Good luck with it anyhow.

S.SubZero · Post by **S.SubZero** » Sun Aug 19, 2007 3:51 am

The 4-pin header should even be keyed in a way that the 3-pin fan connector can be plugged in properly. This is how it is on my Intel boards anyway.

Verbal Kint · Post by **Verbal Kint** » Sun Aug 19, 2007 4:14 am

I confirm that the Gigabyte P35 motherboards can use "normal" 3-pin connector fans connected to those 4-pin headers. The instruction manual even explains how the BIOS can control the speed of the 3-pin fans using the thermal data of the processor rather than PWM.

zistu · Post by **zistu** » Mon Aug 20, 2007 7:26 am

I just finished a build based on the Intel DG965WH board. This board has several fan connectors as well, some 3 pin and some 4 pin. I'm still experimenting with the setups to see what works best, but did find one interesting thing.

My initial setup was as follows:

CPU Header (4 Pin, PWM) - Arctic Cooling 120mm 4 Pin PWM fan.
Rear Chassis Fan (3 Pin) - Nexus Real Silent 120mm fan.
Front Chassis Fan (3 Pin) - Nexus Real Silent 120mm fan.
Auxiliary Rear Chassis Fan (4 pin, PWM) - Nexus Real Silent 120mm fan.

After doing some testing, I discovered that the Nexus fan on the Auxiliary 4 pin header always ran at full speed, and did not get controlled by the mainboard. The other 3 fans were running at around 400 RPM, and did seem to display some form of controlled behavior.

I had another Arctic Cooling fan, so I went to this setup:

CPU Header (4 Pin, PWM) - Arctic Cooling 120mm 4 Pin PWM fan.
Rear Chassis Fan (3 Pin) - Nexus Real Silent 120mm fan.
Front Chassis Fan (3 Pin) - Nexus Real Silent 120mm fan.
Auxiliary Rear Chassis Fan (4 pin, PWM) - Arctic Cooling 120mm 4 Pin PWM fan.

As I had hoped, changing the 3 pin fan to a 4 pin fan on the 4 pin header gave the mainboard control over the fan. Instead of the Nexus running at around 1000 rpm constantly, the Arctic Cooling fan spun at 400 RPM, exactly what I had hoped for.

Another small observation, both 4 pin leads on the main board seem to be controlled by the same controller, and not individually based on thermal zones. This means that if my CPU fan ramps up due to a high temperature, the fan connected to the other 4 pin PWM lead will automatically follow it. In my case this works out as it should, but I can imagine setups where this does not work.

So, in short, connecting a 3 pin fan to a 4 pin connector on the mainboard will spin your fan, but it may not allow the board to control the fan as well.

It makes sense in a way, PWM fans run at ~12 volts and their speeds are controlled by the pulse signal send over the fourth wire. Connecting a 3 pin fan without the fourth wire would just make it run at 12 volts constantly, which concurs with what I observed.

I do however expect this to differ per board and per manufacturer, the Gigabyte boards may take an entirely different approach. And there seem to be many different fan controller ASICs around as well. Just thought I'd share my findings.

To be complete, links to the fans I used (and their final connections):

Nexus Real Silent 120mm fan (Front & Rear Chassis)
Arctic Cooling 120mm 4 Pin PWM fan (CPU, Aux)

Edit: added something I forgot, and added a few minor clarifications.

Jason W · Post by **Jason W** » Thu Aug 23, 2007 10:58 am

Okay, I can confirm that I can attach the Nexus 3-pin fan to the 4-pin motherboard fan headers. Crisis avoided.

Wibla · Post by **Wibla** » Thu Aug 23, 2007 11:27 am

on my P5W DH Deluxe the PWM controller for the cpu fan (4pin) can control 3pin fans aswell, no problems

seemingly.random · Post by **seemingly.random** » Mon Aug 27, 2007 7:51 pm

zistu wrote:So, in short, connecting a 3 pin fan to a 4 pin connector on the mainboard will spin your fan, but it may not allow the board to control the fan as well.

The Gigabyte GA-965GM-S2 4pin sysfan connector supports and controls both 3 & 4pin fans.

The cpufan connector on the abit nf-m2 supports control of pwm fans but runs 3pin fans at 12v only.

So there appears to be no standard.

Most mb's that have pwm cpufan support have the option of controlling pwm fans with pwm or voltage. Because pwm control is more precise, the more responsive speed changes can, ironically, be annoying if don't have a very quiet fan.