Author Options:

can i use a PMBLDC motor as a generator? Answered

can i use a PMBLDC motor as a generator? if so what would be the power and voltage generated by a PMBLDC motor which has a 12V and 40w rating?



3 years ago

if you turn an induction motor's shaft faster than the rated RPM, then you will produce the frequency and rated power of the motor. For permanant magnet variaces, you should spin the shaft at the rated RPM.

It will generate approximately 12V (AC) and 40W, IF YOU TURN IT AT THE ORIGINAL RATED SPEED.

Which may be 30,000 RPM!

Most Brushless motors have 3 or more sets of windings so you will get 3 or more separate phase out of it.

I have seen it done before.  Old computer hardware often has a lot of small motors of this kind.  For example, computer cooling fans, and also the old floppy drives, use this kind of motor.

For anyone reading this thread who is wondering about the acronym, PMBLDC stands for permanent magnet, brushless, direct current

This kind of motor is essentially a permanent magnet AC motor that has been married to an electronic controller.  The controller runs on DC, and basically makes the AC required by the motor, by alternately switching on and off different windings on the motor.

So the usual first step for making a generator from a PMBLDC motor is to remove the electronic controller.  Then you are left with an arrangement of permanent magnets and windings.    

If I remember correctly, the last time I took apart a floppy drive motor, the windings were in some kind of 3-phase arrangement, with 3 terminals.  I am guessing that would be a good match to a 3-phase bridge rectifier. 

Regarding voltage, the magnitude of the open-circuit voltage, across any of these windings, will be directly proportional to speed at which the permanent magnets move past the windings. That just comes from the dPhi/dt term in Faraday's Law.

Also it is like Steve said, if you can get the rotor turning as fast as it used to turn before, in its life as a motor, then the voltage on those windings will be approximately the same.  Also the amount of power the windings can handle is the same as before. Thus approximately: 12V AC, at 40 W, at the same angular speed.