Anonymous
Anonymous asked in Science & MathematicsEngineering · 10 years ago

# Can a shaded-pole motor be used as a generator?

I am an engineer student currently building a generator from a shaded-pole motor (Fasco model D289: 6 coils, 120v, 1050 RPM). I plan to build a new rotor with permanent magnets, so that the rotation of the rotor will induce current in the armature coil. The plan is to only keep the armature of the shaded–pole motor, because of its six coils with iron core perfectly molded and spaces 60 degree apart. I decided not to modify the rotor but make a new one. I will make a 24 side polygon which 4 adjacent sides will be within 60 degree. In other words 4 magnets will be side by side with the same polarity, and the fowling 4 will be of the opposite polarity (each pair = 60 degree on the rotor circumference). Thus my rotor magnetic fields will be perfectly aligned with the 6 coils of the stator.

I just examine my armature and it will be impossible to remove the shading coil because when it was manufacture the shading pole was the first thing installed on the frame, and the coils were wrapped around it. The only thing I can do is to cut a notch on the ring to break it.

my questions are:

(1) Will the armature be more efficient at generating electricity and being a motor with or without the shading coils?

(2) What will breaking the continuity of the shading coil do? Will it make the armature a regular squirrel cage? Will it remain a shaded-pole motor but with a less powerful shading coil? Will it be better or able to be a motor/generator?

Francis

franc_08@hotmail.com

Update:

As I said I am building a flywheel, thus I have to design the system for three state:

(1) Motor spin the flywheel to its maximum RPM.

(2) Flywheel spin on magnetic bearings to minimize the energy loss over time.

(3) Flywheel spin rotor which generate electricity.

Step (1) the motor:

You said that maybe I should not cut the shading coil because:

“without the shading of the poles, the unit when motoring will have no preferential direction to rotate. It won't be able to "make up its mind" and will just vibrate back and forth. You will have to provide some means of spinning it up close to synchronous frequency, and then it will pull in and act as a motor.”

Also “It will not be better as an induction-generator than a motor without the shaded-coil construction” http://www.control.com/thread/1295664953

My motor “might” not be self starting without the shading coil (I don’t understand the theory if it will or not be self starting after changing th

Relevance
• 10 years ago

I think by "armature" you mean "stator". Armature usually refers to the rotating part. I use the terms rotor and stator (as in rotating and stationary) to preclude ambiguity.

A shaded pole motor is an induction motor. Overspeeding an induction motor turns it into an induction generator. All induction generators have to be connected to a source that provides reactive support. Connection to a synchronous generator works. There also have been some clever schemes using capacitors to allow an induction generator to work in stand-alone fashion.

In your case, you are converting the shaded pole induction motor into a synchronous generator (or alternator) by placing permanent magnets on the rotor. That should work. And if you apply AC power to the stator, you will have a synchronous motor.

1) I will guess that the stator will be slightly more efficient without the shading since you won't have the joule losses in the shading loop, and the magnetic axis will stay centered. However, I'm not great at understanding the math behind the magnetics.

2) Breaking continuity will stop the shading. The principle depends upon current flow in the loop setting up an opposing magnetic flux. You can read here how that works:

http://www.brighthub.com/engineering/electrical/ar...

Will it make the stator a regular squirrel cage? No. The squirrel cage refers to the construction of the rotor in induction motors whereby the rotor has a several single loops of copper, into which current is induced, which in turn generates the magnetic field in the rotor that interacts with the magnetic field in the stator. The loops of copper look like a squirrel cage. In your case, you will have a rotor with permanent magnets, and no induction loops.

Without the shading of the poles, the unit when motoring will have no preferential direction to rotate. It won't be able to "make up its mind" and will just vibrate back and forth. You will have to provide some means of spinning it up close to synchronous frequency, and then it will pull in and act as a motor. You can spin it in either direction.

I've never heard of someone using a PM rotor with a shaded-pole stator. It seems as though the shading and shifting of the magnetic field would provide a weak rotation to get the rotor started, but if you have four magnets side-by-side occupying 60 degrees of travel, I think it might not start because the field shift over the first one-half cycle won't be enough to rotate the rotor through 30 degrees. It works with an induction rotor because the field in the rotor slips (or progresses slowly) when the rotor first starts to turn, so effectively its as if the induced magenetic poles are much closer together that 60 degrees. I don't know if my description makes sense. One thing you could try would be to alternate the poles, (thereby making it a 24-pole machine instead of 6-pole, which will decrease the nominal speed by a factor of 4) and see if that will start.

To reiterate, once the motor is up to speed, it will motor whether or not you have a shading coil.

As a generator, if it is stand-alone, you can run it at any speed you want and it will generate electricity. But if you connect it to the grid, then it will have to run synchronously with the grid. And you have to connect in phase or risk major rotor damage (as in bent shaft).

EDIT 1-23-2011: I defer to Vshade's comment about 12 poles, not 24 poles. In retrospect, I think 12 poles is the better answer.

• 4 years ago

• Gone
Lv 6
10 years ago

Violet has answered your questions quite thoroughly. I think that I should comment on the placement of the magnets. Placing six magnets so that three north poles will be adjacent to each other on one side of the rotor and three will be adjacent to each other on the opposite side of the rotor will form a 2-pole rotor. That is appropriate if you intend to connect the six stator coils to form a 2-pole stator. I think that you can form a single-phase, 2-pole stator, but the salient configuration of the coils would be more appropriate for a 3-phase, 2-pole stator or a single-phase, 6-pole stator. If you want to build a 6-pole machine, the magnet polarity should be alternated around the circumference of the rotor.

PS1

I think that Violet is wrong about making a 24-pole machine. Each coil could form 2 poles to make a 12-pole machine, but I think that the stator iron configuration would prevent that.

PS2

The shading coils provide a rotating field in one direction or the other. Without the shading coils, there is a fixed north-south direction that increases, decreases and reverses with the AC voltage alternations, but it does not rotate. If the magnets are not perfectly aligned when the power is applied, there will be torque to rotate them into alignment. With a low-inertia rotor, the motor is likely to start rotating in one direction or the other. With a flywheel load, the motor may not start even with the shading coil.

• 10 years ago

No....The shading pole determines the rotation of the output shaft @ 120 volt Ac @ 60 hz.@ about 1050 rpm.

I have never seen a shaded pole motor larger than about 1/4 hp.

Most are 10 Th. hp.

Breaking the shading pole will stop your motor from running at all.

Bro

Source(s): Years of working on electric motors