Does my motherboard know the size of the PC fan?

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absorb333

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Mar 20, 2013
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Does it know the size of the fan to correctly adjust the speeds?

If the fan slot was designed for a 120mm, and i put in a 90mm, would it get to much oomph and spin faster, therefore louder?
 
Solution
cin19
1) The MB don't recognize the size of the fan. It depends on the control signal, like pwm for the 4pin fan connector or voltage for the 3pin fan connector.
2) If your MB has the 4 pin fan header like http://www.overclockers.com/forums/attachment.php?attachmentid=92908&d=1300219923 and the fan has the 4 pin connector too, then the MB can control the fan speed by pwm based on temperature. The 90mm fan will spin faster than the 120mm one, because it need more air to cool down the temp. So the 90mm will make more noise.
3) If your MB has only 3 pin fan header or the MB has 4 pin fan header but your fan is the 3pin one, then the fan will be controlled by the voltage. like...
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skit75

skit75

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Oct 7, 2008
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The speed of the fan is determined by the fan itself given a certain voltage(usually +12V). Your motherboard can lower or raise the voltage given to the fan to slow it down or speed it up.

Example:

An 80mm fan will usually spin above 3000rpm @ +12V. It is smaller and must spin faster to move the same amount of air.

Connecting a 120mm fan to that same +12V will only spin it at 600-1500 depending on fan. The larger fan can spin slower to move the same amount of air.

The coils in the fan itself determine its native speed @ the given voltage.

Your motherboard does not know the size of the fan but it can determine if it is connected or not(loaded circuit Vs. unloaded circuit)
 
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cin19

cin19

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Mar 14, 2011
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1) The MB don't recognize the size of the fan. It depends on the control signal, like pwm for the 4pin fan connector or voltage for the 3pin fan connector.
2) If your MB has the 4 pin fan header like http://www.overclockers.com/forums/attachment.php?attachmentid=92908&d=1300219923 and the fan has the 4 pin connector too, then the MB can control the fan speed by pwm based on temperature. The 90mm fan will spin faster than the 120mm one, because it need more air to cool down the temp. So the 90mm will make more noise.
3) If your MB has only 3 pin fan header or the MB has 4 pin fan header but your fan is the 3pin one, then the fan will be controlled by the voltage. like http://1.bp.blogspot.com/_4MZ6SdKB7IM/TRWLvokedVI/AAAAAAAAACw/MFWX_USYJ9Q/s1600/4pin_or_3pin_fan_connector_on_m_b_362.jpg
Also If you has the asus brand motherboard you may use the asus fan xpert to control the fan speed.
 
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