CPU coolers with PWM: can't you set FIXED rpm?!

[Dance123]

Hi,

First of all, what exactly is this "PWM chip" alot of CPU coolers seem to have?!

For example Arctic Freezer 7 Pro has this:
"The PWM chip in the motor allows an exact fan speed control over the BIOS. (4 wire)"
"Fan Speed: 300 - 2500 RPM (controlled by PWM signal)"

Am I understanding it correct that CPU coolers like that which have a PWM chip let this PWM control the rpm speed based on your CPU temp it reads from the BIOS or something?!

Does this mean that if your CPU temp changes alot when you go alot from idle to load alot, the rpm speed of your CPU fan will also change alot, which can be really annoying to hear or can you set a fixed rpm somehow?! How do you set a fixed rpm if this is possible?!

I intend to get a Core 2 Duo with an Asus 945P or 965 chipset motherboard.. will these allow me to set a fixed rpm for those PWM CPU coolers since it seems the BIOS controls those coolers' rpm speed, right?!

Or can't you have manual (fixed) control over the rpm speed if the cooler uses PWM?!

Anybody could please explain this?! Should I better get a CPU cooler without PWM chip or can you set a fixed rpm that doesn't change all the time when your CPU load and temp changes?!

 

[Dance123]

Nobody at all who can help with the above question please?!!

 

[thecoolnessrune]

PWM stands for Pulse Width Modulation and is a much more accurate method of controlling fan speeds over the traditional voltage adjustment. It also removes the humming noise inherent in some fans when their voltage is lowered. Speedfan *might* be able to control it, but IMO why would you want to? When idle the fan will be silent, and when under load it will be louder. But it wouldn't spin that fast unless you were in danger of overheating. So leave it alone and give it a chance first. You'll most likely not notice it at all.

Additionally, you need a motherboard who's CPU fan header is a 4 pin PWM header and not the traditional 3 pin.

EDIT: PWM works by using the same 12 volt power, but extending or shortening the pulses sent to the fan. Thereby slowing it down or speeding it up. Since it uses a constant 12 volts, fans sensitive to voltage drop will not make that humming noise.

 

[Baked]

Newer mobos like the P965 come w/ 4 pin fan headers. I've used the AC Freezer Pro 7 on my Gigabyte DS3 mobo, fans are set to auto in BIOS. Works just fine. You worry too much.

 

[masuta]

I have just set up an e6400 on a gigabyte 965 s3 and an e6600 on an asus p5b deluxe.

On the gigabyte the m/b is able to control the fan speed very well and I was quite happy with it, however on the asus I found that q-fan didn't work, it just stayed on the minimum fan speed all the time. If I used AI gear I could change between maximum RPM and minimum RPM (ie the highest "gear" would set the fan speed to full but all of the 3 other speeds set the fan to mimimum) I am hoping that it is a bios problem and that it will be fix in a future release. Speedfan doesn't work for the P5B yet AFAIK, but it is hoped that it will be soon.

 

[zephyrprime]

You can control it in the bios and in mb manufacturer supplied utilities if the manufacturer was nice enough to provide those items.