Fans slow down when CPU goes to 100% - Normal?

[goatzool]

This is a silly question, but I can hear my fans slow down when a program begins to make full use of the processor, like folding@home or Prime95. I assume this is because the motherboard and processor are suddenly drawing more voltage. But should the 12 volt output drop like that? I am expecting to get an upgrade PSU soon and wonder if this is normal and will continue?

 

[larva]

not exactly normal

I see from your sig you have an Asus motherboard. Make sure you have the "Q-Fan" feature disabled as it may be affecting the fan's rpm. Most likely you are testing your power supply's output though, you might try loading the Asus probe software and checking the stability of your voltages. Ideally you should see very little (or no) deviation in voltage over time, and the Asus probe will allow you to review your voltages over the course of time.

 

[JDXNC]

I used to get that when I only had a 250W PSU, once I got a 300W it went away.

 

[goatzool]

Thanks, Larva and JDXNC,

I have Q-fan disabled. I watched Probe and saw confirmation, but something peculiar. When the system goes from idle to load, the 12 volt output drops by a bit more than 1% and the Vcore output drops by more than 3%. However, the 3 volt output goes up about 1%.

I am encouraged that this may not happen with the Antec True 430 due to arrive today. In fact, maybe the crappy PSU explains why I can get to an fsb of 124 with default Vcore bt can't get to 133, even at 1.725. Maybe at the crucial boot moment, the Vcore drops too far.

I'll try to remember to post results in this thread when I swap PSU's.

 

[goatzool]

Fed Ex brought the Antec yesterday. Several things have changed.

First. the chassis fan header on the mobo stopped working.

The fan that remains in service (attributed to CPU but I'm water cooled) does not slow down under load.

The Vcore voltage still drops when the load is applied.

I am able to run prime95 stable at an fsb of 120 instead of 115 (?!). I guess a cheap power supply is partly responsible for introducing errors into computations at 100% CPU load.

I am not any more successful in booting to 133 fsb. Will go on to try vid pin bridging with rear window defogger paint.

I am at least persuaded that power supplies make a performance difference.