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crazydog 08-19-2007 10:34 PM

3 phase
 
Hi everyone, I have a question on 3 phase motors. Can a 3 phase be rewired to single phase ? if so how do you do it ? Thanks Jim

Stubbie 08-19-2007 11:56 PM

No possible way to rewire a 3 phase motor motor to single phase. I've been told there is a rotary phase converter that is sometimes capable of letting a 3 phase motor run on single phase but I'm not sure of the details.

Stubbie

SecretSquirrel 08-20-2007 06:34 AM

An AC inverter or what is commonly known as an AC variable speed drive (VSD) can be used with an input of 240VAC single phase to an output of 240VAC 3-phase. The inverter gives you the capability of speed control of the motor if that would be of any benefit, otherwise the controller can be wired to run the motor at full output. Depending on the HP, an inverter can get kind of pricey.

See http://www.driveswarehouse.com/Drive...s/Compact+VFD/

Is this for a piece of woodworking equipment? There are application considerations when choosing a drive for a specific need. Example; centrifical loads (fans, pumps) vs. torque control. A sales engineer should be able to give you guidance in specifying the correct type of drive.

crazydog 08-20-2007 09:39 AM

3 phase
 
Hi , so you essentially need a phase converter? how about switching motors out with a single phase? Thanks Jim

SecretSquirrel 08-20-2007 09:51 AM

Quote:

Originally Posted by crazydog (Post 58561)
Hi , so you essentially need a phase converter? how about switching motors out with a single phase? Thanks Jim

What do you mean? Changing the motor out? Yep, no problem as long as you maintain HP and frame size. Both parameters will be found on the nameplate. This is assuming a smaller HP motor. You haven't mentioned the HP... that would be good info to know.

I looked into the possiblity of getting the motor rewound but that's a "no-can-do". You can rewind a single phase motor to three phase but not the other way around because of space limitations.

crazydog 08-20-2007 09:59 AM

3 phase
 
Hi squirrel , yeh thats what I meant change the motor out that would have the same hp and voltage requirements. I have an oppurtunity to get a 3 phase welder and air compressor . I have 220 in the garage but its single phase. I was curious wether you could change 3 phase to single phase . Thanks Jim

SecretSquirrel 08-20-2007 10:06 AM

Jim, before you lay out the money for this I'd get the existing motor data and make sure you can find a replacement motor. There is a point of diminishing return... at some point as the motor size starts getting bigger the likelyhood of finding a single phase replacement starts getting smaller. I need to scrounge up a motor data chart before I can tell you when that starts happening.

crazydog 08-20-2007 10:23 AM

3 phase
 
Thanks squirrel, yep planned on doing just that. I'll give more info when I find out. the hp frame size and anything else i can get. right now though I'm just shopping . Thanks Jim

SecretSquirrel 08-20-2007 10:31 AM

You mentioned air compressor and I imagine that it has a 5 or 10 HP motor on it. I just dug into my Grainger catalog and you can get up to a 10HP/215T frame motor but you ain't going to like the price... lists at $891.50. Also as you look at the motor data, pay attention to RPM also.

Good luck and let us know how it turns out.

Mart 08-20-2007 12:26 PM

Phase converters
 
Quote:

Originally Posted by Stubbie (Post 58540)
No possible way to rewire a 3 phase motor motor to single phase. I've been told there is a rotary phase converter that is sometimes capable of letting a 3 phase motor run on single phase but I'm not sure of the details.

Stubbie

I am no expert on phase converters but I have had some experience with them. We needed to get a 3 phase table saw running last winter so we built our own rotary phase converter. To do this you need to first buy a static phase converter. The one we bought was capable of starting up to I think a 7 hp 3 phase motor. Once started the phase converter can be turned off and the motor will run by itself. But the problem with this is the motor is only running on 2 legs, producing only 2/3 of its rated hp. This was not going to work with our tablesaw. We got a 5 hp 3 phase motor running on two legs of power and used the third leg coming off the motor to generate power. With the help of the static converter we were able to get a second motor (10hp) wired in line and started. With these two motors alone we could turn off the static converter and had two motors running on 2 legs. With these two motors we could generate enough power on their third legs to run a third 3 phase motor (10hp) at full power. We ended up drawing off of all three motors in order to get full power out of our saw. We bought our motors at salvage yards and had some laying around. So it was cheaper for us to do it this way. You need to make sure your service is big enough for this. We were dimming lights on the whole farm starting up. Also make sure you talk to your electrician, or better yet have him do it since he's licensed. Your dealing with high voltage (240) so be careful!

Stubbie 08-20-2007 10:47 PM

Wow! Mart that was some resourceful engineering, thanks for sharing.

stubbie


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