Be Quiet! Silent Wings 3 PWM fan in old DC only motherboard

ConradWebster · 1 Dec 2021 at 15:08

The exhaust case fan in my 13-year-old pc finally started packing in so I purchased a 120mm Silent Wings 3 PWM fan, to eventually keep as a spare with a new build. The motherboard is an Asus P6 Deluxe with only 3 pin chassis connections and Q-fan control for DC fans. I read that connecting a 4 pin plug to the 3 pin header is okay, merely leaving off the pin that delivers the PWM voltage. I have enabled Q-fan to that fan set to standard and it appears to be acting as a DC fan, HWinfo64 telling me it is spinning at around 1200rpm, slightly ramping up on pc use. Am I right in what I have assumed? Incidentally, HWinfo64 also tells me my CPU fan is either at 0 or around 84000rpm!

doyll · 1 Dec 2021 at 18:09

Definitely right, no problem at all using 4-pin PWM fans on 3-pin variable voltage headers.
3-pin header has no pin-4 for PWM control to pulse the constant 12 power on PWM pin-2 to adjust fan motor speed as needed.
No problem at all because on variable voltage header has variable voltage on pin-2 to fan motor adjusting motor speed as needed.

1200rpm fan speed is pretty easy to hear. Assuming it is running 1200rpm, couldn't you adjust fan curve to slow it down when system isn't generating much heat?

Sounds like either CPU fan speed circuit is bad or motherboard speed sensor is bad.

ConradWebster · 1 Dec 2021 at 18:15

Thanks for the informative reply. The old fan rattled along like a train which we got used to so this is more than acceptable.

Drumroll · 6 Dec 2021 at 19:41

The easiest solution is simply limit the rpm by voltage control, or use one of those adapters that limit the fan speed, but personally I would simply set a range and leave it alone.
One thing to note is to avoid the fan ramping up and down. This is more annoying than a constant fan at high rpm.
If the fan curve is based on the CPU temperature, for example, I would start at:
up to 50C, 50%
up to 70C, 60%
over 75C, 70 or 100%.
Not sure how low you can go on DC, 40%, I guess.
Leaving the first interval too low or too close between them will cause the fans ramp up and down all the time.

ConradWebster · 6 Dec 2021 at 21:50

The motherboard is an Asus P6T Deluxe 2008 so I only have Q fan control rather than UEFI controls available now. I am running the 4 pin PWM fan on 3 pin DC on standard. True, the ramping up is noticeable but I don't think any better control is possible. The quiet setting might not give enough cooling.

ConradWebster · 7 Dec 2021 at 15:10

Changed it to the quiet setting which runs at 1000rpm to 1200rpm as opposed to the standard which started at 1200rpm. Very quiet and cooling is fine.

doyll · 7 Dec 2021 at 15:35

Sounds like a job well done!