[mythtv-users] Fancontrol with replaced CPU fan

Yan Seiner yan at seiner.com
Mon Oct 12 23:05:54 UTC 2009


On Mon, October 12, 2009 3:54 pm, Johnny wrote:
>> I always thought if you plugged a 3 pin fan in these 4 pin pwm headers
>> you would get no voltage control and the fan would run at full power
>> always.
>
> I think you are right. On the 4-pin headers the PWM is on the 4th pin.
> So when you plug in a 3-pin fan you only get the standard power with
> no PWM. But on both of my Asus motherboards they have a feature they
> call Q-fan that lets the bios regulate the 3-pin chassis fans as well.
> According to fancontrol and pwmconfig these 3-pin headers are able to
> use PWM. I have another 3-pin header for the power supply fan that
> doesn't have any PWM control (or Q-fan). So they must do something on
> the motherboard to allow for the PWM control on some of the the 3-pin
> headers, and it is different than whatever they do with the 4-pin
> headers. They are specifically designed so that you can put a 4-pin
> fan on a 3-pin header and a 3-pin fan on a 4-pin header, and they will
> work at full speed, but you won't have PWM control in either case.

Google is your friend.

http://www.allpinouts.org/index.php/Motherboard_(CPU)_3_Pin_Fan_Connector
http://www.allpinouts.org/index.php/Motherboard_(CPU)_4_Pin_Fan

The difference, apparently, is the power.  The 3 pin ones are regulated
via PWM directly so are limited to less power, the CPU fan must have a
transistor or something that allows higher power draw while being
regulated by PWM on the extra pin.

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