# 3-phase Motor on Single Phase



## wildleg (Apr 12, 2009)

I think its gonna burn up, but that's just me. would be nice to see some labels, pics, model #'s, or anything that could be construed as information.


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## maryland (Nov 16, 2011)

Hope these pictures are large enough to see... little trouble meeting the size limit on the photos...

Thanks!


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## wildleg (Apr 12, 2009)

ok, maybe it won't burn up. try calling them http://www.consew.com/default.aspx
maybe you can get a schematic


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## Hippie (May 12, 2011)

You just hooked the 240 up same as it was wired with the 120? That can't work out well :-\ from what I can tell it is a single voltage motor so no windings that can be changed correct?


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## maryland (Nov 16, 2011)

That's correct, it's a single voltage motor. And I hooked it up to 220 basically the same way it was hooked up to 110. Any ideas?


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## Hippie (May 12, 2011)

Was it wired this way from the factory? I would assume it was ok running on 120 since with the increased voltage it was still <220 but now its way over that and loud/hot, I would say run a new circuit, probably cheaper for them than replacing the motor. Or when it burns up and replace it with a 480v motor lol


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## Wirenuting (Sep 12, 2010)

That's an OEM motor and won't last long being rewired.


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## maryland (Nov 16, 2011)

No, definitely not wired that way from the factory... i was wired by somebody who clearly wasn't an electrician (no wirenuts, just tape, no connectors, no respect for colors, etc.) but who clearly knew how to make it run.

I think I agree with you guys that it's going to eventually burn up. But what's up with the capacitor? Why does that work? And where do those "wild" voltages come from?

Just curiosity now... I'll pull a new circuit!

Thanks a lot!


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## Dennis Alwon (May 9, 2009)

Pull a 3 phase circuit and do it correctly. :thumbsup:


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## maryland (Nov 16, 2011)

Would love to, Dennis, but only single phase available, being fed from a generator :-/


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## Dennis Alwon (May 9, 2009)

maryland said:


> Would love to, Dennis, but only single phase available, being fed from a generator :-/


What about a phase converter?


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## Wirenuting (Sep 12, 2010)

I believe it works along the same idea as a fan used atop large AC multi fan condenser units. One motor is wired different to give it the variable speed capable of over taking the reverse pinwheeling. 

Many years ago I saw an old guy change one of these style sewing machine motors in a hospital. We had a seamstress on site.
It was a 3 phase we pulled out and I didn't understand how he made it work. Since I was new and we were in a hurry, he promised to show me next time. That was 20+ years ago and the seamstress retired and the old partner died. :-(


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## oldtimer (Jun 10, 2010)

Wirenuting said:


> I believe it works along the same idea as a fan used atop large AC multi fan condenser units. One motor is wired different to give it the variable speed capable of over taking the reverse pinwheeling.
> 
> Many years ago I saw an old guy change one of these style sewing machine motors in a hospital. We had a seamstress on site.
> It was a 3 phase we pulled out and I didn't understand how he made it work. Since I was new and we were in a hurry, he promised to show me next time. That was 20+ years ago and the seamstress retired and the old partner died. :-(





Do you believe in SEANCES? :jester: :laughing::laughing:


P.S. I like to laugh at my own jokes! :laughing::laughing:




Oh wait! I'm dead ... ... I'll ask around for you!


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## jmsmith (Sep 10, 2011)

Hippie said:



> You just hooked the 240 up same as it was wired with the 120? That can't work out well :-\ from what I can tell it is a single voltage motor so no windings that can be changed correct?


While you can run it ok off 120V, it will not take long to burn-up at 240. The capacitor is there to shift voltage to the unwired lead, creating the "phantom" 3rd phase. This is the basic setup of a homemade phase converter. I can't remember the formulas, but you can balance the voltages/currents on the windings by varying the capacitance that is installed. The reason it won't last long at 240, though, is because you will generate a "wild leg" that will be over your winding rating of 240V. The motor would have to be rated at least 480V to keep from burning up. I like Dennis' idea, run either three phase OR change motor to single-phase. :thumbsup:


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## mattsilkwood (Sep 21, 2008)

You can get a single phase 1/2 hp motor for like $100. That's the direction I would head.


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## micromind (Aug 11, 2007)

A static phase converter is nothing more than a capacitor. The output is the two legs of the input going straight through, and the capacitor is connected between one of the incoming legs and the 3rd motor lead. 

What you have here is nothing more than a field built static phase converter. 

If you connect the motor to 240 instead of 120, it won't run very well as it is. You'll need to change the capacitor. About 28 µf per HP will work. A bit more if there's any load on the motor when it starts. 

Always use a capacitor rated for continuous duty. Motor run and ballast capacitors will work, motor start capacitors will not.


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## niteshift (Nov 21, 2007)

i heard generator.
if so, it has to be a big enough capacity for the load. otherwise motors will have problems running efficiently.
sewing machine motors must see a lot of dust and dirt. motor looks ancient. 
if you have 120 now, why not just buy another motor. they aren't expensive as stated earlier i think. there a commonly stocked part at our area supply stores.
i see your in dc area, theres a graingers and a mcmaster-carr as well as many other sources for motors.
they can fix you up with exact replacement, any associated cords, belts, plugs, its a big place. not much they don't have. 
if gen is still the problem, you'll need to remedy that issue.


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## swimmer (Mar 19, 2011)

I show 110V between #1 and #2, 155V between #2 and #3, and 190V between #1 and #3. 

Well, I can explain this part and answer 1 question.
Yes, the capacitor is making a another phase and I have also seen this done on UL and CE approved industrial equipment.


The capacitor provides a 90 degree phase shift rather than the 120 degree shift normally associated with 3 phase power.


190 = SQRT( 110^2 + 155^2)


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## John Valdes (May 17, 2007)

This has been done for years after market when someone screwed up on the order or someone was trying to make something work on the cheap. 
The correction for this setup is to remove all the wires. Pull all of them out and get a small chassis mount VFD. Or go pick up a 120 volt motor at Grainger.
Here is an example of a small chassis mount VFD. Inexpensive and simple to install and set up.


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## Forsythe (Feb 6, 2012)

Use a drive. ATV12H037F1. Rated 1/2HP, 2.4A, 230V for three phase motors with 115VAC single phase input. $200 list price per their website.


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## maryland (Nov 16, 2011)

Super valuable information here. Thanks guys. Really appreciate the explanation behind the wild voltages, Swimmer. Takes me back to AC Theory class!

Now, the VFDs... Do you guys recommend these because they permit me to save power use on the circuit like I was trying to do with the 240V circuit? Looks like they'd run on 120V; do the VFDs pull less amps than the motor itself would? Or do they just correct the phase shifting and make the motor run more efficiently?

All good ideas and I appreciate your help. This is definitely a situation where people were trying to get them to run on the cheap. The only reason I was trying to get them to run on 240V was to maximize the number of machines I could install before maxing out the generator. In the end, I'm guessing I'll just have to add more 120V circuits to handle any future machines.

Thanks a lot!


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## Forsythe (Feb 6, 2012)

maryland said:


> Now, the VFDs... Do you guys recommend these because they permit me to save power use on the circuit like I was trying to do with the 240V circuit? Looks like they'd run on 120V; do the VFDs pull less amps than the motor itself would? Or do they just correct the phase shifting and make the motor run more efficiently?


They will save power, especially if you only run up to 90-95% of full power (if you can). Also, they do limit the inrush to less than 1.5x FLA, reduce mechanical wear, etc.


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## kaboler (Dec 1, 2010)

You guys are smart, and I like it.


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## John Valdes (May 17, 2007)

Forsythe said:


> Use a drive. ATV12H037F1. Rated 1/2HP, 2.4A, 230V for three phase motors with 115VAC single phase input. $200 list price per their website.


That would make the net cost somewhere around $100.00 using a .50 multiplier. Excellent price. Who makes it. You did not tell us who the manufacturer is.



maryland said:


> Super valuable information here. Thanks guys. Really appreciate the explanation behind the wild voltages, Swimmer. Takes me back to AC Theory class!
> 
> Now, the VFDs... Do you guys recommend these because they permit me to save power use on the circuit like I was trying to do with the 240V circuit? Looks like they'd run on 120V; do the VFDs pull less amps than the motor itself would? Or do they just correct the phase shifting and make the motor run more efficiently?
> 
> ...


Ist. You never saved any power by running things on 230/240 volt. You lowered current, which allowed you to add more to the generator load. You were saving no money, or running more efficiently.

Yes. The VFD inputs 120 volt single phase and outputs 230/240 3 phase to operate 3 phase motors.
No. The motor still uses the same amount of power at base speed. There are savings to be considered, but not in this application.
Yes. The addition of a VFD will give you 3 phase power for the motor and speed adjustment if needed. (be careful when running motors to slow). But it does not make the motor more efficient, unless you can find a benefit that the VFD provides that you can use that you have not mentioned. Motor efficiency is determined by the motor itself.

Note: Adding a VFD to line powered motors can ruin a motor. The sign wave is a simulated AC sign wave and is dirty power. This can takeout older motors not designed for inverter use.
The addition of a load reactor can help in this regard. The reactor will clean up the sign wave and knock down any IGBT spiking. If the motors are small and easily replaceable, you can try the VFD out before buying the reactor.


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