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Polarity of fan motor? Answered

Recently I had occasion to change the small fan that cool the aluminum fins just above the exturder. Not paying too much attention to the polarity of the 12 volt supply voltage, I figured that if was turning the wrong way, I could easily change the plus and minus connection. When I fired up the controller, I thought it was turning the wrong way and I changed the polarity. It then wouldn't turn at all. Changing it back to the original polarity, it worked fine. It is normal to have the fan polarized, and if so, what is the proper direction of air flow?

Alan

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Josehf Murchison
Josehf Murchison

6 weeks ago

Sounds like a brushless motor in the fan. Flip the fan over.

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Orngrimm
Orngrimm

6 weeks ago

Thats a normal behaviour. See, the fan nowadays is not only a DC-Motor on a Supply. In there is a controller and all sorts of stuff... Often temperature.sensor, Tacho-signal-generator and whatnot. Open an old fan and see what you can find. Cool sunday evening-project.
Said that, it is logic, that with reversed polarity, nothing works abnymore:
For starters, the controller is powered in reverse. They normally a are protected against wrong polarity, but it will not work as you basically connect VCC of supply to GND of the controller and GND of supply to VCC of the controller. There will be no signal generated for the Stepper-motor (Yes, those fans are stepper and not DC) to turn...

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liquidhandwash
liquidhandwash

6 weeks ago

You cannot reverse the direction of a brush-less fan. However you can usually fit the fan back to front which will reverse the air flow. I would think that the air needs to blow onto the heat sink.