Reversing fan direction for CPU cooler

[weeber]

I have an Antec Jet Cool fan on my Athlon. It's not great, but it seems to get the job done. Anyways, I've discovered that instead of blowing air on the CPU, it's sucking air from it. I believe that reversing the fan direction would help improve cooling. I thought that by splicing the wires and switching red-to-yellow and yellow-to-red that the fan would reverse direction and start blowing air on the CPU. Instead, the fan doesn't start at all. Going back to the normal configuration, the fan works fine.

My question is, what's preventing this procedure from reversing the direction of the fan? I've tried this a couple of times, and each time the normal configuration works fine, but the reverse configuration does not work at all. Replacing the fan really isn't an option, becaue it uses pegs glued into the heat sink instead of screws and I'm not really sure how to take them out.

Any ideas?

 

[Necrolezbeast]

uhh, take the screws out then flip the fan...

 

[weeber]

Necrolezbeast, again the fan is attached by pegs that are glued in. Once I take it off, I'm not really sure if I can get it back on. Besides, there's no guard on the other side of the fan, so if I just flip it over it will only drag against the heat sink and won't work.

 

[ThisIsMatt]

My question is, what's preventing this procedure from reversing the direction of the fan? I've tried this a couple of times, and each time the normal configuration works fine, but the reverse configuration does not work at all.

DC brushless fans (like all muffin fans you'll find in computers) don't work the same as a typical dc motor. They use electronics to control the magnetic pulses required to turn the fan blades. In a typical dc motor, you have coiled wire on the drive shaft and a magnet around the coils, with brushes touching multiple contacts around the shaft's surface to provide electricity to the coils in alternate fassion. The shaft then turns while the magnet and the brushes connected to the motor & magnet housing stay still. On the other hand, with a brushless motor the magnet is attached to the fan and moves with the fan. Since the coils are not moving now, they have to be switched somehow. This is done electronically with a series of transistors, capacitors, resistors, and most relevant to this discussion, diodes In short, diodes only operate in one direction polarity-wise. So when you switch the polarity of the "motor", you're fighting diodes. I'm not clear, however, on the necessity of the diodes -- I just know that this is your problem.

 

[weeber]

Wow, ThisIsMatt, what a great explanation. I never know that so much went into these simple little fans. I guess you learn something new everyday.

 

[ThisIsMatt]

No prob

Here are some pictures from a delta I just tore apart

Fan
Fan (coils)
Fan (electronics)