need old pc motor to rotate both ways? How?

[EWILLUSTRATION]

Have an old pc motor, the motor only goes one way I need it to rotate both ways. Why will it only go one way? Can I get it to rotate both ways? If so how?

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[SunEagle]

Have an old pc motor, the motor only goes one way I need it to rotate both ways. Why will it only go one way? Can I get it to rotate both ways? If so how?

[ATTACH=CONFIG]2736[/ATTACH]

Unless there is a mechanical stop the keeps the fan from rotating in either direction you should be able to make it go both ways.

All you have to do is reverse the wires (+ and - polarity) and the motor will go in the opposite direction. Be aware that the fan blades are design for their best performance for a specific rotation. Going in the opposite direction will move air but not as efficient as the direction is was designed for.

[EWILLUSTRATION]

I think I must have a mechanical stop. Anyway to disable it?

Already tried to reverse the wires (+ and - polarity) will not work. Only goes one way.

I think I must have a mechanical stop the keeps the fan from rotating in either direction. Anyway to disable it?

[SunEagle]

Already tried to reverse the wires (+ and - polarity) will not work. Only goes one way.

I think I must have a mechanical stop the keeps the fan from rotating in either direction. Anyway to disable it?

If you can't rotate the fan with your finger (no power) in both directions then there is a mechanical stop that is probably built into the motor. If you can manually rotate the fan blade then it still may be the type of DC motor they are using and it is wired so it only goes in one direction.

If you had a small DC motor and hooked it up to a battery you can see that it will reverse when you change the wire polarity. I am not sure why your PC fan doesn't reverse.

[Sunking]

Already tried to reverse the wires (+ and - polarity) will not work. Only goes one way.

Then it has steering diodes.

[FunGas]

Take the sticker off, you'll see a small circuit there, you can't modify it, use another type of motor.

[edit] I made a cyclone style vaccuum using the blades of one of those fans fitted to a remote control car's main motor, which is reversible and powerful enough.

[Naptown]

Easiest way to make it spin backwards is remove and reinstall in reverse. What was the front is now the rear.

[SunEagle]

Then it has steering diodes.

Nice catch Sunking. I hadn't thought of that.

[Sunking]

Nice catch Sunking. I hadn't thought of that.

Just simple deduction. Muffin fans are series wound and direction or rotation is determined by the polarity. Plus I know a lot of muffin fans use a diode bridge to make them rotate in one direction only. In addition I do some DIY EV work and have a racing golf cart.

[PowerSupplyGuy]

Muffin fans are brushless DC motors. There are three windings on the stator, while the magnets are on the rotor. If you can get in there with some fine tools you will have to swap any two of the three wires going to the windings. That will reverse the direction.

[inetdog]

Muffin fans are brushless DC motors. There are three windings on the stator, while the magnets are on the rotor. If you can get in there with some fine tools you will have to swap any two of the three wires going to the windings. That will reverse the direction.

I thought that just worked for three phase AC motors? Unless there is a control circuit which pulses the DC separately to each of the three windings, I cannot see a brushless DC (permanent magnet on rotor) motor even spinning at all.

[PowerSupplyGuy]

It is actually a 3 phase DC motor. It has a 3 phase inverter which runs in a 6 step fashion rather than pwm. It's like comparing a modified sine to PWM inverter.

Here is a nice treatment of brushless.

http://cache.freescale.com/files/product/doc/AN1916.pdf

The only problem I can envision is orientation of Hall sensor in regards to motor direction. Micro uses hall sensor to determine rotor position. This information is then used to time the commutation between poles. It is very muck like an ignition in an automobile. Information derived from distributor shaft position in relation to cap determines which plug fires.

[bcroe]

Reverse

Some of the 24VDC & 48VDC motors I worked with (up to 300 CFM), used a single coil & a hall
effect sensor. It could jerk in either direction, but the sensor and an integrated circuit controller
quickly figured it out & got it going the right way. I believe these could be reversed by moving
the sensor relative to the coil. With solid state, reversing the leads didn't reverse rotation, but
could blow the electronics if without (energy wasting) steering diodes. Bruce Roe

[PowerSupplyGuy]

Some of the 24VDC & 48VDC motors I worked with (up to 300 CFM), used a single coil & a hall
effect sensor. It could jerk in either direction, but the sensor and an integrated circuit controller
quickly figured it out & got it going the right way. I believe these could be reversed by moving
the sensor relative to the coil. With solid state, reversing the leads didn't reverse rotation, but
could blow the electronics if without (energy wasting) steering diodes. Bruce Roe

Yes, you are correct - You cannot reverse the red & black leads and expect to get the motor to reverse rotation. You must remove the rotor by taking out the little C clip under the label. Then you must swap any two of the three wires going from the controller to the coils on the stator. It takes a little bit of precision. I believe controller will still know what to do with feedback from hall sensor and motor will spin backwards, but not absolutely sure. OP will have to try for himself.