phase converter and transformer question

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But the number of poles may *not* be reduced to 1/2 the normal number. If the split windings are on the same physical poles, and only electrically isolated, there should be no problem. I just got through typing a fairly long response (which you will not yet have had a chance to see) in another branch of this thread.

It depends on the design. Two-speed motors are connected just this way. I have even had a three-speed (2-pole, 4-pole, 8-pole) as the capstan motor on a reel-to-reel tape deck. It also was designed as an "inverted rotor" one, so the rotor doubled as a flywheel. Actually, it had three independent sets of windings. It was a cap-run motor, and fairly low torque. I spent some time learning to re-wind motors when that one burned up. And then, once I got that right, the bearings gave out. :-) It *did* come from a hamfest, and the whole deck cost me something like $2.50. :-) I later got an Ampex 440B to replace it. And the 440B has a two-speed (by switched windings) Hysteresis-synchronous motor -- with a separate flywheel. The motor was made by Bodine.

That's the reason for the flywheel. :-)

Because, in reality, all of the *poles* are energized -- just separate coils sharing each pole. This is apparently a function of who made the motor. Some have shared windings and can act as an autotransformer, some have separate windings, and can't.

Enjoy, DoN.

DoN

My opolgies - I was assuming the windings, like the ones indicated on the name plate of the motor were always located on seperate poles. That is - all the motors I've seen dont have the poles share stator locations. I just have to study more and post less.

Jerry

Jerry

The right sort of machine needs to be one that is wound with two independent sets of 220v three phase windings. Either winding is a complete set and capable of being used on its own from a 220v supply.

This means that each slot contains two bunches of conductors - one for each set - series connected for 440v, parallel connected for 220v. Because the bunches of coductors are closely coupled, one leg can behave as an auto transformer.

It's also possible to use the distribution that you've assumed - a 4 pole distribution of the windings which is arranged for 220v supply to one pair of poles and

220v to the remaining pair. The two pairs are series connected for 440v or parallel for 220v operation.

With this arrangement the two sets of conductors are widely separated and too poorly coupled to act as an effective autotransformer.

An off the shelf 4 pole motor cannot be reconnected to make it behave a 2 two pole motor because the winding distribution is wrong - each phase is designed to produce four field maxima 90 deg apart. Efficient 2 pole operation needs two maxima 180 deg apart. The best that reconnection of a standard motor an do is to produce a distorted two pole field that has dip at the all important

180 deg point. Two speed motors have a different winding distribution to overcome this problem.

Jim

Thanks Jim

I do need to learn more about these motors. I guess that, since I'de never seen a 3 phase motor with poles that contain both windings, I assumed they were either nonexistant or *very* rare.

I'd like to gather up enough energy to reconnect a 220/440 3 phase motor and try the method enl_public describes. I'll try to locate a motor that might allow reconnection so the 440 '3 phase' can be gotten from a single phase 220 power source

Jerry

No need for aplogies. Certainly not to me.

I don't think that I've ever seen a motor nameplate which really made it clear whether the windings shared poles or were on opposite poles. They were just concerned with how to set up the interconnections for normal use at the two voltages it was designed for. Why document for non-standard use? :-)

Enjoy, DoN.

Right you are, Don! The subject matter of this thread is so far afield from ordinary design practice any attempt to reconcile the original poster's "concept" is ludicrous. Far be it from me to belittle an idea containing even a shred of usefulness in the home shop. This thread, however, goes beyond ridiculous. As our English friend pointed out, it may be possible with a certain type of (rare) motor and then only if one is able to put up with gross inefficiency and start-up problems. All in all, an interesting concept albeit one that will see very, very limited use in the home shop. IMO, the original poster broached an enticing idea, but one that he either lied about or had no practical experience with. He generated a thread that would bring immense pride to any other troll.

Bob Swinney

Well, I *asked* if he had actually done that. His lack of response speaks for itself - I'll take that as a "no."

Jim

Thanks very much for input from everyone!