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Alternator from washing machine motor?

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LAN_403

Dr. Shark

Mon Jan 29 2007, 12:26PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I recently had the chance to remove the motor from an old washing machine. Now I am considering my options what to do with it. I don't really know what type of motor it is, but I think it is a type of squirrel cage induction motor that has a big capacitor connected to it to fake a third phase out of ordinary 230V mains power.
Probably the most fun and educational thing would be to construct an alternator of sorts. I can easily spin up the rotor with an electric drill and it has a fair amount of inertia, so at least I have a way to get mechanical power into the system.
Knowing close to nothing about alternators I am probably overly enthusiastic here; it seems that an induction motor cannot be simply run in reverse as an alternator, but I would have to wind a rotor coil. To energize this armature coil I would come up with some sort of commutator, which would be probibitively difficult.

So, what are my options? Is there any way this could be made to work, or is it a pipedream?

Marko

Mon Jan 29 2007, 01:12PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

It seems that both synchronous and asynchronous machines can be ran as motors and generators.

Asynchronous ''squirrel cage'' machine can be turned into a generator, simply by supplying some reactive power (wich magnetizes the rotor) and spinning it up OVER it's synchronous speed.

Capacitors are placed over windings, and 3-phase mains is connected to it just as if it was a motor. Then it can be spun up to sell power back to mains (nice, sine wave of exactly same frequency and phase).

BTW, I have no clue how would you do this for a single phase motor, I'm not sure if it would work just as it is.

Such a generator is obivously practical in cases where you need to sell power to mains, but as a stand-alone alternator you'l be in trouble using it. You would need either a separate synchronous generator (running at different speed!) or some kind of electronic circuit to excite the async machine.

afaik.

Bjørn

Mon Jan 29 2007, 01:25PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

An asynchronous motor will work fine as a generator by adding capactors.

It will not work if started with a load.
It will not work again if stopped with a load.
This is because it depends on a remnant magnetic field in the rotor to get going. If it fails to get going then you can magnetise it with a DC current for a few seconds before starting it.

Itis not good at driving inductive loads because that will cancel the effects of the capacitors.

The picture shows how you would connect up a typical motor that is made to run with the fake third phase. The size of the capacitors depends on several variables.

Dr. Shark

Mon Jan 29 2007, 01:35PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Thanks BjÃ¶rn (sorry, I dont have that other umlaut), that schematic seems to fit my motor exactly. It also has six cables labeled U1 V1 W1 U2 V2 W2, so now I know how connect it.

I also found some good stuff about alternators here:

And specific information about converting induction motors to permanent magnet generators here:

Finally some general stuff about different types of motors here;

Oh, and this is what my motor looks like, taken apart:

I wonder if it would be possible to run this as a "pulsed alternator" aswell, so I could use it to power some of the gizmos that usually require a big capacitor bank. It seems that compulsators work on _very_ different design principles, but maybe it is possible to "compensate" this type of alternator too, so I can extract larger current pulses than the current impedance of the armature would allow.

EDIT: I thought some more about this. The following is a collection of random ideas how all this might work, so dont bother to read unless you think you can step in and help me!

The only clear information about the principles of compulsators I could find was here

(near the bottom) it seems that the key to "compulsation" is to cancel the magnetic fields created in the rotor and stator coils. This momentarily reduces the inductance of the winding to virtually zero, so a big current pulse can be obtained.
What I don't understand is the advantage "alternators" provide over induction motor-type designs. Clearly it is an advantage not to need slip rings to inject current into a moving coil, if the current can simply be provided by induction. In ordinary alternators the rotor only seems to regulate the output voltage, so maybe injecting a large current here will give an output in the kV range without the need for many windings?
On the other hand however, if the current in the exciter and the stator have to cancel for "compulsation" to take place how can more current be extracted than is provided via slip rings into the rotor?
Or wait, the compensation winding is a separate, third coil, right? But why is it needed, if the rotor and stator in an ordinary induction motor automatically produce equal and opposite magnetic fields? And how is it powered?

Damn, this is harder than I though. I hope somebody can shed some light on this.

has some details, it indicates that a compulsator is an aternator with an additional "squirrel cage" between the rotor and the stator. Phew!

some good stuff in the archives:

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