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Hello all

I have an opportunity to buy a 1970 Unisaw for very cheap. So cheap that I will still be ahead if I need to replace the motor. I am confused on what is needed to run a 3 phase motor. Can I do this out of a normal circuit box or do I need to get a phase converter? I thought all I needed was a 240-40 dedicated circuit. Also is it cost effective to get a phase convertor? Thank you all for your time.

Branum

PS the motor is a 3hp-3phase motor, I would like to run the original motor in my shop and not have to swap out to a single phase motor.
 

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3-phase is only available in industrial areas. In essence, 3-phase comes in two voltages, 220 and 440 volts. If you have a home workshop it would be highly unusual for you to have access to 3-phase current.

I looked into 3-phase converters a year ago. What I found was the purchase of a 220 volt 3-phase converter would cost more than the purchase of a dedicated 220 volt single phase motor. There are two types of 3-phase converters - solid state and the use of a modified electric motor to convert the current from 220 volt single phase to emulate 220 volt 3-phase. After talking to an expert on this I was advised that the less expensive solid state converters would do the job but were prone to failure under starting current surges. He strongly recommend the use of the modified motor method. This leads to buying one motor to drive the other motor. This makes sense for some situations like industrial-type metal lathes and milling machines where the motors are pretty much built into the machine. But for a Unisaw you might as well just buy a new 220 volt single phase motor or even consider a 110 volt motor if you don't have access to 220 volt single phase. Most homes have 220 volt single phase for ovens and stoves. Also, you need to understand that 220 volt single phase current is made up of two 110 volt circuits that are 180 degrees out of phase. I did a lengthy write-up about this on this website for another thread a few months ago. Do a search on this website and on the Internet for more information.

Rufus
 

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You will need to get a phase converter. I have a Kay Industries converter. You might also need to get what is called a Buck\Boost transformer in order to balance out and regulate the proper voltages. My voltages are about 1 volt difference between them. The electronics on one of my machines requires a close voltage tolerance for it operate properly. You may not need the transformer. You will know once the converter is hooked up. You will also need a disconnect switch with fuses and a switch to turn on the converter. It sounds like a lot of work and quite an outlay of money. However, I believe this route gives one a way to purchase heavier machinery at a much lower price. Three phase motors also are less expensive and last longer than single phase motors.
Get at least a 7 1/2 HP converter. The Kay converters are true converters in that the company rates their converters stating the Hp is the starting Hp per motor at a time and running up to three times the stated HP at the same time.. For example. You have a 7 1/2 HP converter. You can start up to a 7 1/2 HP motor and then another 7 1/2 HP motor and then a third 7 1/2 HP motor. This gives you a total of about 22 HP running at the same time.

Most of the other brands of converters give you the maximum total HP as their rating.

This is a major difference when choosing a converter.

John
 

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When I had to move out of the Industrial location I had (with three phase) into my current location(residential) I ended up buying a used Rotophase Converter for cheap($150). It runs the Unisaw,3hp 3ph and the compressor 5hp 3ph, just fine. (Rated at at 5hp) You just have to remember to turn it on a bit before powering up the saw or compressor.

All it is is a large 440 motor that starts using capacitors. Once running it generates the third leg of the 3 phase. You could build one yourself without capacitors, just get it turning with a rope and a pulley like you used to have to start a lawnmower, then kick on the power. There should be some info on the web about it. If it is wired right you can get the third leg out of that.
 

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like I recommend to everyone who is in your situation, go to

www.factorymation.com

and buy the TECO FM50 variable frequency drive (VFD). This model work for 1hp tp 3hp and costs about $150, and will last about 20 years, so I'm told.

the hookup is relatively straight forward but I recommend removing the motor and push button station (and magnetic starter if it has one) from the cabinet and pre-wire it all up on your work bench. make sure it works then mark and identify the wire connections using masking tape and a magic marker. The just put it all back in the cabinet and wire it back together based on the identifying tape marks. you are good to go. PM me if you want some wiring diagrams from a true expert (Richard at OWWM), or search for VFD at OWWM and you will come upon them.
 

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I'll second the drive idea. Today's drives are so cheap and reliable, they make phase converters obsolete. IMO
 

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Branum, 220 to 240 is all the same. If this is a do it yourself deal, I would recommend going with some one with good customer service. I don't know factorymation, but have seen them highly recommended on here numerous times. You definitely want to go with a drive that will give you full power, not an electronic converter that only puts out 2/3.

I am an electrician, commercial and industrial.
 
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