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Too low RPM on exhaust fan

Last response: in Components
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June 7, 2012 1:36:22 PM

Hello!

I just baught a new case fan, as I didn't have an exhaust. But It's only running at 700-750 rpm, which to me (I'm no expert) sounds far too low, and it feels incredibly weak when I hold my hand infront of it. I think I may know the cause of the problerm, but no idea of how to fix it, so perhaps one of you fine gents can tell me.

My motherboard is an ASUS M5A78L-M. Looking at my motherboard diagram, it only has 2 visible fan connectors - a 4-pin 'CPU_Fan' and a 3-pin 'CHA_Fan'. The fan I baught was an Arctic Cooling F12 PWM 120mm. The fan came with a 3-pin power plug, with just a yellow wire running to it, connected to a 4-pin PWM socket adapter, from which was the 4-pin PWM plug.

Seeing as my motherboard only had one 4-pin socket, I unplugged it, plugged to case fan in, then removed the 3-pin power plug from the 4-pin PWM socket, in place for the CPU fan, THEN connected the 3-pin power plug into the 3-pin 'CHA_Fan' socket.

The CPU fan (which is running off the same socket as the chassis fan) is running fine at about 2200 rpm, so does anybody know what the deal is?

Any help is much appreciated!


More about : low rpm exhaust fan

a b ) Power supply
a b V Motherboard
June 7, 2012 4:46:34 PM

I tried to decipher the connection you described but it is quite hard to imagine. Can you post a picture?
June 7, 2012 9:48:56 PM

randomkid said:
I tried to decipher the connection you described but it is quite hard to imagine. Can you post a picture?










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a b ) Power supply
a b V Motherboard
June 7, 2012 11:39:28 PM

OK, let's clear some things up.

First, the 3-pin connector that only has one yellow wire does not power the fan. The yellow wire only reports rpm to the motherboard.

Second, that Arctic Cooling fan you bought is designed to be daisy-chained with another 4-pin PWM fan to run off a single header. So, you have both the CPU 4-pin fan and the new fan plugged into and getting power from the same motherboard header. This is just fine if that's what you want. Both CPU fan and the new fan will increase and decrease RPM based on the CPU temperature (but the new fan RPM is being reported to the chassis fan header). Hope you're not confused.

Anyway, the two fans plugged into the same header have different RPM's because... they are different fans and they are designed to run at different RPM's. That is perfectly normal.

Now, if you want the exhaust fan to run at full speed you can just connect it's 4-pin power lead to the 3-pin chassis fan motherboard header. It's keyed so you can only plug it in one way with one pin of the 4-pin off to one side of the motherboard header. That will improve airflow, but might be noisy because the fan will only run at full speed.

I say leave it plugged in the way you have it unless you are having overheating problems. I've actually used those exact Arctic Cooling PWM fans and find them to be a nifty way to connect multiple PWM fans.
June 9, 2012 1:05:15 AM

rwpritchett said:
OK, let's clear some things up.

First, the 3-pin connector that only has one yellow wire does not power the fan. The yellow wire only reports rpm to the motherboard.

Second, that Arctic Cooling fan you bought is designed to be daisy-chained with another 4-pin PWM fan to run off a single header. So, you have both the CPU 4-pin fan and the new fan plugged into and getting power from the same motherboard header. This is just fine if that's what you want. Both CPU fan and the new fan will increase and decrease RPM based on the CPU temperature (but the new fan RPM is being reported to the chassis fan header). Hope you're not confused.

Anyway, the two fans plugged into the same header have different RPM's because... they are different fans and they are designed to run at different RPM's. That is perfectly normal.

Now, if you want the exhaust fan to run at full speed you can just connect it's 4-pin power lead to the 3-pin chassis fan motherboard header. It's keyed so you can only plug it in one way with one pin of the 4-pin off to one side of the motherboard header. That will improve airflow, but might be noisy because the fan will only run at full speed.

I say leave it plugged in the way you have it unless you are having overheating problems. I've actually used those exact Arctic Cooling PWM fans and find them to be a nifty way to connect multiple PWM fans.


Thank you very much for the thorough answer! I just plugged the 4-pin PWM plug into the 3-pin CHA_FAN header like you said, and it now runs at about 1200rpm (which is still a bit lower than I'd like it to be, but works fine).

OH, and the reason I referred to the yellow 3-pin plug as the power plug, is because that's what the instruction manual labeled it as :')

Thanks again!
!