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  #1  
Old 07-25-2011, 08:43 PM
tonyfranciozi tonyfranciozi is offline
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Default Converting a 3-phase 230v motor to single phase 120v

Hi all,

First let me say, excellent forum! This is my first post but I've been lurking for a while now.

Ok, I have an industrial sewing machine from the 1930s that runs on a 1/3 horsepower 3 phase 210/230v AC motor. I'd like to run it on single phase standard 120v. I was looking into building a static phase converter but, from what I understand, that would reduce the motor's power by a third and could lead to overheating and eventually shorten the life of the motor.

My question is, what is the feasibility of rewinding the motor to run on single phase 120v power? I do have Rosenberg's book on motor repair and rewinding, but I'd like to get more advice on the matter.

Thanks for any help you can provide!
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Old 07-25-2011, 09:36 PM
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strantor strantor is offline
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(disclaimer: I don't know 100% what I'm talking about)

semi-educated guess: I don't think it's possible. The fins where the windings go into the stator would probably be set up in a configuration divisible by 3 for the 3 phases. It probably would not work for a configuration where the windings need to be divisible by 2.

There are "3 phase converters out there" which is basically a single phase motor coupled to a 3 phase generator; I've heard works and sounds feasible but never actually seen one.

Probably best to get a new motor IMO
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Old 07-25-2011, 10:13 PM
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Could you post a diagram of a "static phase converter" just for my own education?

I suggest a professional motor winding shop could tell you about feasability, maybe for free.

I've seen single phase to 3 phase converters of the motor/generator type. They work wonderfully, but expensive and have moving parts to wear out. There would be less number of moving parts in a correctly wired motor you would buy. I bought a 1/4 hp motor for $65 last week. For this job, I'd be buying a motor in a New York minute.

Still, if you want to learn about winding motors, that's a good enough reason to do it yourself.
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Old 07-25-2011, 10:20 PM
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Are you positive the motor is actually three phase? If it is a variable speed sewing machine motor, a lot of them are actually a DC motor and VFD(variable frequency drive). Takes in three phase rectifies it to DC and drives the motor. Some of them can be used on single phase 220V by just using two of the input lugs.

What is the make and model of the motor?
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Old 07-25-2011, 10:22 PM
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Quote:
Originally Posted by shortbus View Post
Are you positive the motor is actually three phase? If it is a variable speed sewing machine motor, a lot of them are actually a DC motor and VFD(variable frequency drive). Takes in three phase rectifies it to DC and drives the motor. Some of them can be used on single phase 220V by just using two of the input lugs.

What is the make and model of the motor?
did they have that technology in the 30's?
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Old 07-25-2011, 11:10 PM
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There are passive-static single-phase to 3-phase converters. Suggest you go to http://freepatentsonline.com and sign up for a free account. Then look up patent numbers 4777421, 4484125, 3673480 for a tip-of-the-iceberg peek at various approaches to your task.

You may also wish to avail yourself of offers for plans to build single-to-three-phase converters. One example: http://tinyurl.com/3r3lbj5

o wis The choices fall into two classes. A rotary converter (teamed single and three phase motors) will be the most efficient and least sensitive to actual load as long as it's large enough. A static capacitor/inductor network (also mentioned in the plans) is probably the best approach . . . but these are not as efficient. They'll choke off about 30% of your motor's output capability leaving you with a 1/4 horse motor (which might be sufficient to your needs).
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Old 07-25-2011, 11:15 PM
tonyfranciozi tonyfranciozi is offline
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Here is a photo of the specs plate pinned to the motor's case. You can't see it in the photo but it specifically says AC.

I'm looking in Rosenberg's book now and the only difference I can see between a three phase and single phase, besides the way they are wound, is the centrifugal switch that shuts off the starter winding of the single phase when the rotor reaches speed. I might be able to attach such a switch to my current rotor?

The only reason I hesitate to get a new motor is because this is the original motor that came with the machine. Well, that and I've always wanted to rewind a motor but never had a decent excuse to!

I don't have a diagram of a static converter, but I was reading about them here: http://www.metalwebnews.com/howto/phase-converter/phase-converter.html
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Old 07-26-2011, 12:03 AM
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Quote:
Originally Posted by tonyfranciozi View Post
Here is a photo of the specs plate pinned to the motor's case. You can't see it in the photo but it specifically says AC.

I'm looking in Rosenberg's book now and the only difference I can see between a three phase and single phase, besides the way they are wound, is the centrifugal switch that shuts off the starter winding of the single phase when the rotor reaches speed. I might be able to attach such a switch to my current rotor?

The only reason I hesitate to get a new motor is because this is the original motor that came with the machine. Well, that and I've always wanted to rewind a motor but never had a decent excuse to!

I don't have a diagram of a static converter, but I was reading about them here: http://www.metalwebnews.com/howto/phase-converter/phase-converter.html
There are different types of motors even within the single phase category. not all of them use a centrifugal switch with starting cap. some use a run cap.
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Old 07-26-2011, 12:27 AM
tonyfranciozi tonyfranciozi is offline
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Quote:
Originally Posted by strantor View Post
There are different types of motors even within the single phase category. not all of them use a centrifugal switch with starting cap. some use a run cap.
So the motor could start without a centrifugal switch? Would the run capacitator connect to the rotor, or just the stator?

I guess what I'm getting at is, could I do this without messing with the rotor at all? I don't want to throw the rotor off balance if at all possible.

I'm really not worried about losing a third of the power, the machine could certainly run on 1/4 HP. My only worry would be overheating.
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Old 07-26-2011, 01:55 AM
tonyfranciozi tonyfranciozi is offline
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Now I'm thinking that I could scrap the centrifugal switch altogether and just use a start-and-run capacitor. Can anyone see a reason why this wouldn't work?
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