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Topic: need help to reverse the direction of a brushless motor (Read 4 times) previous topic - next topic

Chagrin


Just yesterday I tried to run a laptop cooling fan backwards by hooking the battery up back-to-front, and it didn't start.

Do brushless DC motors actually even run backwards?


A brushless fan as found in a computer contains the controller within the fan and that controller is only designed to spin the fan in one direction. Fundamentally though, brushless DC motors are certainly reversible.

FWIW there are zillions of RC cars with brushless motors and reverse capability.

retrolefty

best if you posted about a specific motor, but most classic 3 phase DC (and 3 phase AC motors) can be reversed by simply reversing any two of the three wires.


JimboZA



A brushless fan as found in a computer contains the controller within the fan and that controller is only designed to spin the fan in one direction. Fundamentally though, brushless DC motors are certainly reversible.

FWIW there are zillions of RC cars with brushless motors and reverse capability.


Thanks- what what I expected. Or, at least I would have been surprised if they couldn't run both ways, and thought there might be something in the motor preventing it. I wonder why though?- the plug is made to fit one way only, and since the fan is hidden inside it's not likely to get connected back to front in use.
Roy from ITCrowd: Have you tried turning it off an on again?
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terryking228

I suppose it's possible to reverse two of the 3 wires in a small brushless motor, with tiny reed relays or Fets. But is it worth it??

Also, the timing of the hall effect rotation sensor is sometimes optimized for one direction, I believe.

A few years ago someone was using a 4 inch fan that was reversed to control the draft on a wood stove, but I bet that was a brush type motor.

How about mount two identical fans in opposite directions and turn on one or the other??
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Zapro


Just yesterday I tried to run a laptop cooling fan backwards by hooking the battery up back-to-front, and it didn't start.

Do brushless DC motors actually even run backwards?

Jim


Inside a computer fan is a control IC - it's actually a small computer with state machine and all. This switches 3 coils on the motor, making the magnet ring turn. For feedback there is sometimes some hall-sensors too. Usually all this circuitry is built in a single component with 3 to 5 legs soldered to a small circuit board. Reversing the polarity on the wires would be like putting in power to the Arduino in reverse - you wouldn't want to do that - right ?!
There is no way of reversing the fan direction without modifying it heavily - and then the fan blades do not work in reverse - look at the profile on them, fan blades and propellers only work the "right way" round.

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