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  #1  
Old 12-30-2011, 09:56 PM
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iron ant iron ant is offline
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Converting 3 phase motor to single phase

I just aquired an older Speedair 5hp air compressor. I was told it was single phase, but when I showed up and saw 4 wires comming from the motor, I knew it was not. The guy at Grainger wanted to sell me a 600 dollar motor, said i could not convert it, but I know better, I think. Does anybody know about inverters?, and is that what I need? thanks, im trying to set up for a big blue air hammer and I need the increased psi....eric
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Old 12-31-2011, 11:40 AM
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tonofelephant tonofelephant is offline
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Re: Converting 3 phase motor to single phase

Eric you sure it is 3 phase? Is it specifically stated that it is a 3 phase motor? Just thinking that my dryer has 4 wires & is 220 volt but not 3 phase.
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  #3  
Old 12-31-2011, 12:48 PM
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Re: Converting 3 phase motor to single phase

There are several different ways to do this.
There are what are called "static" convertors, which allow a 3 phase motor to start, but dont generate true 3 phase.
These usually dont work great on compressors, but I did manage to get one to run my 7 1/2 hp compressor for a few years.
http://www.phase-a-matic.com/StaticDescription.htm

Then, there are rotary phase convertors- these are the best, they generate true 3 phase, but they are not cheap.
http://www.grizzly.com/products/G5844
these are pretty much the industry standard-
http://www.arco-electric.com/

Then, you can use whats called a VFD-
http://www.phaseconverterinfo.com/ph...verter_vfd.htm
look on ebay for VFD's- there are a lot of em.

none of these solutions is much under $400, and many of them can cost you quite a bit more- so you need to look at your whole shop needs- will you ever need any other 3 phase tools?
If so, might make sense to pay for a 10hp or bigger 3 phase rotary convertor, and wire up a whole 3 phase subpanel.

If the only tool you will ever need 3 phase is the compressor, I would vote for scouring ebay for a used single phase motor, and switching it over, rather than trying to generate 3 phase.

5hp is about the top size commonly available for single phase, but they are out there, used, for a lot less than $600.

I have 400 amps of 3 phase at my shop- most of my tools are 3 phase...
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Old 12-31-2011, 02:35 PM
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Re: Converting 3 phase motor to single phase

Only the rotary convertors will allow the motor to run at full power. The static type will only put out about 2/3 power. In my opinion, it is better to invest in the new single phase motor, that gives you only one thing to be concerned about.
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Old 12-31-2011, 03:01 PM
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Re: Converting 3 phase motor to single phase

My7 1/2 hp Ingersoll Rand Compressor runs on a single phase 220...real easy hook up, too. I have it wired to a 50 amp breaker, though it only asks for 40.
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Old 12-31-2011, 04:07 PM
Andrew Werby Andrew Werby is offline
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Re: Converting 3 phase motor to single phase

Like Tonofelephant says, this could well be a single or 2-phase motor, which often have 4 wires. Usually, a motor will have a nameplate stuck to it someplace which tells about things like phase, hp, rpms, amps, etc. Look for it before investing in a phase converter. If it is in fact not a 3-phase motor, here's how to hook it up: http://www.ehow.com/how_6454787_wire...olt-motor.html

If it is a 3-phase motor, it's going to be just as expensive to purchase a rotary converter as to replace it with a single-phase unit. The advantage to getting the converter is that 3-phase motors are more rugged and efficient, and you'd be able to purchase more industrial-type equipment, which typically runs on 3-phase, and which most home-shop owners tend to shy away from. But if you don't want any more equipment like this, then just replace it with something easier to run.

Andrew Werby
www.computersculpture.com
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  #7  
Old 12-31-2011, 07:16 PM
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Re: Converting 3 phase motor to single phase

Thanks Guys, as I have never had 3 phase issue or equipment , so I had a feeling some of you had 3 phase power ect. Yes there is that funny little 3 on the motor next to Phase, might not be the sharpest tool in the shed , but im not that dull,,lol .. The compressor was originally made with 6 different motors and flywheel opions, as the guys records only went back to 84 and this has 77 stamped on side. Looks to be in mint condition, and I have to believe the motor is not original??? they used it in a parts assembely,but very little so I am hoping she can handle my day in out wear and tear.
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Old 01-03-2012, 12:57 PM
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Re: Converting 3 phase motor to single phase

I found out if 3 phase motor has 4 wires comming out you can't convert it. If it has 6 wires you can. Hey does anybody have good conections on buying 5hp motors, Grainger ,were pssdair comes from, is kind off high??? Compressor was freebie, but 30 yrs old, is it worth putting $$ into, i don't know, only other option is to guy new 7.5 hp thats about same rating in psi to cfm...
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Old 01-03-2012, 03:22 PM
EJB EJB is offline
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Re: Converting 3 phase motor to single phase

Assuming the compressor suits your needs and will produce air, it would be worth investing in another motor. The motor can easily be half the cost of the unit. Might be a gamble if you have not seen this thing run in the first place. I have not shopped around in a while but I would bet you could find a decent quality used one for about $200 - $300. Might even be able to get some trade in value for your 3-phase from a local shop. Have not bought from these guys in a while but might be worth checking out for comparisons: surpluscenter.com
Good luck!
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