Do 4 pin Sys fan headers control PWM fans?

DTWD · 2 Dec 2011 at 21:16

In other words, will my motherboard stop a PWM fan if the system isn't hot enough?

The reason I ask is that the fan spins up on boot but then spins down and just rocks occasionally. If I plug it into a connector off the PSU (via an adapter) it spins all the time.

Tealc · 2 Dec 2011 at 23:02

It's not normal for them to stop fans. They'll usually run them at low duty cycle below thereshold temps. It could be this duty cycle is too low for the fan, or it's attempting to voltage control the fan, or it's a 5v pwm header. The fact that it spins up at boot suggests it's a PWM controlled fan as theyll often kick them up to 100% on boot.

DTWD · 3 Dec 2011 at 07:04

Hmm any ideas how I go about testing this?

It's defo a PWM fan.

The motherboard is a GB z68xp ud3

Tealc · 3 Dec 2011 at 09:09

According to your manual the Sys_Fan2 header differs from the CPU_Fan header in that pin 4 is Reserve, whatever that means, rather than Speed Control.

SYS_FAN2:
Pin No. Definition
1 GND
2 +12V /Speed Control
3 Sense
4 Reserve

rather than..

1 GND
2 +12V /Speed Control
3 Sense
4 Speed Control

http://download.gigabyte.eu/FileList/Manual/mb_manual_ga-z68xp-ud3-(issd)_e.pdf

I don't know what more to say really. Use a different header and go voltage control? Use a PWM splitter to connect the second/third/fourth to the CPU_FAN header? Use a 3 pin DC fan on Sys_fan2 and use Speedfan to control it. It sounds like the header has voltage control at least on Pin2.

DTWD · 3 Dec 2011 at 10:31

Cheers.

I have it running constantly using the PSU connection at the moment.

It's quite enough that I am happy to leave it. When I see a fan controller I like I might grab one.