why will gpu fan not run in reverse

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6 Nov 2009
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65
hi

i wanted to reverse the direction of my gpu fan so i changed around the black and red wires that feed it

i was expecting the fan to run in the opposite direction but it did not do that

in fact it did not run in any direction

so i had to change them back

why is this ??

cheers
 
Firstly, is this a windup? Changing the wires won't work because one is - and the other is + it won't work. Secondly, why do you want to run it backwards anyway?
 
ok i thought changing the wires would change direction

may be i need to check my theory on dc motors


i wanted to change the way it ran because

at the moment the gpu fan is pulling air from outside the box and exausting the hot air into the box

i wanted it to pull air from inside the box and push hot air out
this is because if it pulled air from inside it would be getting cool air because of the position of the fan is close to the box main air in

but if there no way to change fan direction + fan physice would not work in reverse the i am best keep it the way it is

thanks
 
why is this ??

Because brushless DC fans can only go in one direction. Brushless fans work with a circuit board that knows basically where the magnets are at any time, and know which one to switch on and which to switch off. Having the wrong voltage, in this case -12v would not power the circuitry correctly. Brushless fans are quieter because they have less contact between parts and rely more purely on electromagnetism to drive the rotor around. They last longer, are more efficient and cleaner.

Brushed fans can go either way by reversing polarity but they make more noise as the brushes are in contact with the commutator shaft of the motor at all times. It is this that transfers energy to the motor shaft itself and causes the magnetic field. Brushed fans tend to have sparking too from the contact. Examples would be a power drill, washing machine motor. They spark crazy amounts and you'll find metallic residue near the motor.
 
Yes well the hand test can often be misleading.

A bit of paper is usually a better guide.

Wasn't able to get a conclusive image of the Bliss 7800 GS as it came up with several different types. Some strange looking fans there though.

Edit: Fag paper, yes that'll do it.
 
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