Converting a 3-phase 230v motor to single phase 120v

CDRIVE

Joined Jul 1, 2008
2,219
After rethinking this.. Small 1/3 HP-120V-1PH-1725RPM motors are not that expensive. WW Grainger stocks them. You would probably be better off replacing and saving the motor for the day when you sell the machine to a collector. Check out Grainger on line.
 

CDRIVE

Joined Jul 1, 2008
2,219
Right, but if I were to rewind the motor as though it were a single phase with a starting and running winding would it be possible?
Doubtful that you could accomplish a monumental task like this.

Old industrial sewing machines (definitely Singer) keep the motor running continuously. Power is applied to the drive train via a knee operated clutch. Because of this the starting load is minimal, so a high stall torque motor is not required. This motor will probably do the job for you but searching Ebay might bring up a better choice.

http://www.grainger.com/Grainger/DAYTON-Belt-Drive-Motor-6K778?Pid=search
 

Thread Starter

tonyfranciozi

Joined Jul 25, 2011
10
Power is applied to the drive train via a knee operated clutch. Because of this the starting load is minimal, so a high stall torque motor is not required.
So since there is relatively little load on the motor during starting could the motor start on just a running winding without the aid of a starting winding?
 

CDRIVE

Joined Jul 1, 2008
2,219
Where do you live? Small motors are available at flea markets and garage sales every day... cheap!!! Why screw around with this? If you do some looking you can probably pick one up for < $20.00.

I'm a purist when in comes to vintage machinery. Your vintage motor should not be molested.
 

CDRIVE

Joined Jul 1, 2008
2,219
So since there is relatively little load on the motor during starting could the motor start on just a running winding without the aid of a starting winding?
No. Even with absolutely no load a cap start motor will just sit there and buzz if the start circuit is not engaged. You can hand spin the rotor to start them though.

When shopping for a replacement motor avoid 'Blower/Fan' duty motors, as they provide little torque, even when up to speed.
 
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Thread Starter

tonyfranciozi

Joined Jul 25, 2011
10
I guess I just want to rewind a motor for the heck of it. I think it would be an interesting project. I might document it on my friend's blog.

I understand your point about not wanting to mess with a vintage machine, though I should add that the motor had already been rewired. The way I look at it, if I wasn't giving this motor new life, it would be in the scrap yard right now.

And just to clarify, I'll definitely need a starting winding, but is the start cap absolutely necessary? The Rosenberg book shows a split phase motor w/o a start cap with the starting winding controlled by centrifugal switch. My plan is to forgo the centrifugal switch and control the starting winding manually.
 

strantor

Joined Oct 3, 2010
6,333
I guess I just want to rewind a motor for the heck of it. I think it would be an interesting project. I might document it on my friend's blog.

I understand your point about not wanting to mess with a vintage machine, though I should add that the motor had already been rewired. The way I look at it, if I wasn't giving this motor new life, it would be in the scrap yard right now.

And just to clarify, I'll definitely need a starting winding, but is the start cap absolutely necessary? The Rosenberg book shows a split phase motor w/o a start cap with the starting winding controlled by centrifugal switch. My plan is to forgo the centrifugal switch and control the starting winding manually.
I can't reference this rosenberg book you have, but the link I posted in post#12 shows all the different types of single phase configurations with a condensed explanation of each. just pick the one that looks easiest for you. The previous statement is only because you seem dead-set on rewinding this motor. I still don't think it will work and I advise against it. If you do nothing else, at least record the # of turns each winding and the configuration so that a rewind shop will have something to work with in case your attempts fail. I would hate to see this old motor rendered permanently useless.
 

strantor

Joined Oct 3, 2010
6,333
If you live in the houston area I will give you a fractional horsepower 3phase motor to experiment on. I would hate to see you botch that singer motor. reminds of a few months ago I saw for 1948 tucker for sale. there was something special about it which made it one of 3 ever made. guy found it in a scrap pile. They fixed it up real nice, but they chopped the friggin top! Completely ruined the historical value. That's an irreversible blunder.
 

Thread Starter

tonyfranciozi

Joined Jul 25, 2011
10
As promised, a picture of the machine. It's a Singer 71-101 buttonhole machine. All it does is turn out buttonholes. Alex Kabbaz says this machine makes the best damn buttonholes you can find, past or present, and he made shirts for Michael Douglas!

But anyway, rather than bastardize the motor right off the bat I think I'll just reconnect it to run on 120v and hand crank it to start on a single phase. If that works out OK I'll leave it be. The motor has already been rewired so I won't be hurting the historical value.

Oh, and thanks for the offer strantor but I live in the Philadelphia area. If I decide to do that rewind down the road I'm sure I can pick up an old three phase to practice on for cheap. And thank you all for your patience and advice, I know it's not easy dealing with a n00b!
 

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#12

Joined Nov 30, 2010
18,224
You may be a n00b, but you're smart enough to track the conversation, and that counts for a lot.

ps, can't see why you resist using a start capacitor, I get them for less than $2 wholesale.
 

strantor

Joined Oct 3, 2010
6,333
I think I'll just reconnect it to run on 120v and hand crank it to start on a single phase. If that works out OK I'll leave it be.
What do you mean by "reconnect"? Are you planning on just hooking up 120vac to 2 phases of the 3 phase motor; or are you talking about performing your custom singlephase configuration? If you are talking about the former; I can almost guarantee that won't work. I tried that before (on accident) with a 3phase 480V 5hp motor. When I hooked up the 2 phases (3rd phase wasn't connected on the other end) the motor just hummed. I was able to start it spinning by hand, but I was also able to stop it spinning by hand. NO TORQUE. This will also burn up a motor; referred to by electricians as "single phasing" a 3 phase motor. "what happened to the motor?" ... "it got single phased and burnt up."

If you're still talking about rewinding it for single phase; I really would like to hear how that turns out. I'm curious, never tried that.

The motor has already been rewired so I won't be hurting the historical value.
Rewinding a motor in the original way shouldn't hurt the historical value. If you found a motor that old which hadn't been rewound, I'd be leery of hooking electricity up to it. I just don't think you'll be able to find the data for how it's supposed to be configured so I recommended recording that before you modify it (just in case).
Oh, and thanks for the offer strantor but I live in the Philadelphia area. If I decide to do that rewind down the road I'm sure I can pick up an old three phase to practice on for cheap. And thank you all for your patience and advice, I know it's not easy dealing with a n00b!
no worries I just hope I don't come across as a naysayer.
 

Thread Starter

tonyfranciozi

Joined Jul 25, 2011
10
What do you mean by "reconnect"? Are you planning on just hooking up 120vac to 2 phases of the 3 phase motor; or are you talking about performing your custom singlephase configuration?.
There are instructions in the Rosenberg text on how to reconnect the leads to the winding to reduce the voltage. I was under the impression that a three phase motor would run on one phase, but that it just wouldn't start on one phase, no?

I'm still interested in rewinding the motor as a single phase, but I have a few unanswered questions like what gauge wire to use, and the exact winding confirugation. I know it has to have 4 poles to spin at 1750rpm, but other than that I'm really in the dark. How does a winding shop figure out what configuration to use when an unwound motor comes in?
 

strantor

Joined Oct 3, 2010
6,333
There are instructions in the Rosenberg text on how to reconnect the leads to the winding to reduce the voltage. I was under the impression that a three phase motor would run on one phase, but that it just wouldn't start on one phase, no?
Sounds to me like you're talking about wye/delta wiring. wye is usually used for low voltage (230V usually in my experience) and Delta (480V usually in my experience) This is only for motors where you can access both ends of all 3 windings. if they're connected up inside, you won't be able to change that. if it's rated at 230V then it's probably already hooked up for "low voltage"

not in my experience

I'm still interested in rewinding the motor as a single phase, but I have a few unanswered questions like what gauge wire to use, and the exact winding confirugation. I know it has to have 4 poles to spin at 1750rpm, but other than that I'm really in the dark. How does a winding shop figure out what configuration to use when an unwound motor comes in?
I can't answer that with 100% certainty because I've never worked in a rewind shop, but I'm pretty sure they just take what you give them and redo it. I've always been told that before you do anything with motor windings, you should write it all down because the rewind shop doesn't have anything to go by if you don't. I know that it takes a lot of engineering to determine #of turns, air gap, HP, amp draw, wire gauge, insulation, speed, #poles, etc. I doubt the rewind shop employs an engineer to figure all this stuff out when someone's brought in a motor without windings or with wrong windings. They may or may not have templates of "what works" for different sized motors. I don't know. I do know that sometimes even when you bring the motor still intact they can screw it up and then the motor will run hot.
 
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