Lullaby.DK Tips and Tricks for the technical minded

The ASUS Q-Fan story....

Q-Fan, ensures that the processor fan runs just fast enough to keep the CPU adequately cooled. When using a high performance CPU cooler, only a very low RPM on the fan is needed for adequate cooling. But the Q-fan in the ASUS board do not allow the very low RPM so it will have the fan run at full speed all the time. To work around this, we need to cheat the Q-fan, and make it think that the fan is running faster.

This is my cooling story.

The gear

Case:
Motherboard :
CPU:
Memory:
GFX:
HDD:

Aopen A600A Black
ASUS A7N8X-E Deluxe
2500xp Barton with a box cooler
512Mb Samsung PC3200
GF3ti200
Segate 80Gb + 120Gb

I didn't plan to buy the CPU with the box cooler, but the dealer only had those left....
Anyway that gave me more research time, to find the best cooler for me....

After assembling the machine and tested it, I became familiar with Q-fan function.
Q-fan is a great feature for those of us who would like a quiet computer and the Q-fan worked well with the box cooler.
But the box-cooler was still too noisy for me, and the CPU temperatures a little to high...
So I bought the Zalman CNPS7000A-CU cooler. This cooler is awesome, the CPU temperatures dropped more than 13°c even with the fan set to lower RPM (50-60%). Unfortunately the Q-fan function didn't work with the zalman cooler :-(

I searched the internet to try and find a cure, but it was clear that the ASUS BIOS / Q-fan can only work with high-speed fans (more the 4000rpm). But what would happen if I tricked the BIOS to think that the FAN is running at a higher RPM? This could easily be done with a simple frequency doubler inserted Rotation signal from the FAN.

Building a frequency Doubler

Schematics

The assembled PCB

In the computer

(The IC is a Quadruple 2-input NAND gate -Like this one-)

Testing

The BIOS and ASUS Probe now reports the RPM as twice as high, so the frequency doubler works...
Continuing with CPU temperatures vs. Fan speeds

Note
At idle
After 15min
Extra heat*
Cooling
Cooling
Back to idle

CPU load
0%
100%
100%
0%
0%
0%

Temp.
38°c
44°c
52°c
45°c
44°c
39°c

Fan RPM
1875
1875
2630
2110
1875
1875

^{* I had to use a hairdryer the gain the higher temperature :-)}

Findings and Conclusion

If the CPU temperature is lower than 50°c, the fans RPM will be reduced to 10/15
of full speed (approx 1875rpm), when the CPU temperature reach 50°c the fan speed
will increase to full speed (approx 2600rpm).
So now Q-fan actually works quite well. Even though one could wish for a bios that
allowed a lower idle RPM...

- Frontpage -