Anyone know why my CPU fan speed goes up under load?

[rmzalbar]

When I load up my Tbird 1.1GHz OC'ed to 1.2GHz, my Taisol (the big forged one) with 30CFM fan, the CPU fan immediately increases by 100 RPM. The instant I tell Prime95 to go, you can HEAR it load up. AFAIK, there is no way for the KT7 motherboard to tweak the fan speed based on CPU load, and MBM5 doesn't indicate a significant voltage change anyways. So, I have two theories:

1) The full-on 60-watt (or so) drain into the CPU somehow causes the fan to speed up. I would have thought the opposite to be true, if it's even possible with an Enermax 430-watt PSU.

2) The lower PSU fan, which is rather large and sits just above the CPU HFS, speeds up when the PSU goes under heavier load due to some internal fan speed regulating function, and the air movement across my HSF causes it to speed up. I like this theory the best.

It's very interesting, and, (I think,) rather nifty that I can *hear* my computer working harder. Any other ideas?

 

[SDsucka]

I'm not familiar w/ ur mobo or your fan or your programs... but if there is some kind of sensor that tells you your fan speed, and there is some kind of sensor that tells you your cpu temperature, chances are, somewhere there is a program/firmware, telling your fan to increase in rpms in relation to the cpu temp.

 

[rmzalbar]

Can't be temperature, because it speeds up the instant the CPU goes under load. Not enough time for the temp to change. I can even make it do it just by clicking and dragging on a window drag bar or click-holding on a close button.

 

[Yknot]

Enermax sells 80mm fans with sensors (variable speed). Bet we can guess where they use it on their own products.

From their product spcs: Ball bearing fan with thermal control function. Odd phrasing, but....

Thanks for bringing this up: I hadn't known it about my 430!

 

[skay]

Are you absolutely sure that it's the CPU fan spinning up? The reason I ask is that the Enermax PSUs do spin faster based on temp. So as the temp of the case increases, the fan in the PSU spins faster. Maybe you have the fan connectors for the CPU and the PSU switched on the motherboard (or in MBM)?

 

[rmzalbar]

I'm absolutely certain it's the CPU fan. I just replaced the stock HFS with a Taisol CGK unit with a Delta 30CFM fan on top. The sound of the Delta is very distinctive, and it's easy to hear it speed up. The PSU fan is very quiet, and I couldn't hear the fan change speed with the stock HFS.

The PSU fan is still attached to the same header as before, the only fan I unplugged was the CPU fan, and I took extra care to make sure it goes on the FAN 1 connector because the motherboard shuts down at POST if there is no fan there.
Nope - it's definitely the CPU fan.

 

[lhampel]

The CPU fan will speed up around 100-200 RPM on all ABIT Kt7 motherboards.
Here's what happens...When the CPU load is high the Abit board will raise the +12V a very small amount.
(Stealing the volts from the +5v)

Check your voltages before & after running Prime95.