Building a rotary 3 phase converter

brandon64 · Dec 20, 2011

Do you have any equipment that runs on 3 phase electric but your house or place of work is not so equipped? You could buy a rotary phase converter for about $800-$2500 or with some simple electrical know how you can build one alot cheaper. That's what I did. I bought some plans off of Ebay for $3.00 to build a phase converter, and I spent about $125 in parts. It's nothing more than 2 capacitors 3 relays and an idler motor. And you have to find something to encase all of the said components. I have a 3 phase welder that I needed to hook up at my new house where only 2 phases were available. When I moved into the house there was an old Ironrite enclosed iron( old *** iron, they were popular in the 40's and 50's) but it made a perfect cabinet for my phase converter. I put it all together tonight and it works. If anybodys interested I will share the places I got all of the components, and the wiring schematic. It's really pretty neat. I used a coil bracket off of a 383 intake I had to mount the large capacitor on the bottom left. enjoy.

Cranky · Dec 20, 2011

I have a mill and a lathe and I bought an already made rotary for 1500. This was before I had a computer and had no idea that they could be built like that but mine has a LOT more than a couple of capacitors in it! It'll run 30 hp and will start motors that are rated at 10.

brandon64 · Dec 20, 2011

Cranky said:
I have a mill and a lathe and I bought an already made rotary for 1500. This was before I had a computer and had no idea that they could be built like that but mine has a LOT more than a couple of capacitors in it! It'll run 30 hp and will start motors that are rated at 10.

The one I built is an 8 HP unit. The only difference in the HP rating is the amount of capacitors and there rating, and the idler motor rating. To get 30 HP you would need to run about 8 capacitors, 4 start and 4 run capacitors. You hook them up in parallel. A 30 HP unit would cost about $400 or so to build, (I'm guessing) And if your phase converter is rated at 30HP it should at least be able to start a 15 hp motor.

My welder takes 50 amps at max power and doing the math puts it at about 10 HP, I've welded up to 1/4 inch steel and have not put the heat setting past 20 amps, or approximately 4 HP. So an 8 HP converter should be plenty to handle anything I plan on welding.

Meep-Meep · Dec 20, 2011

I built one a long time ago but I only used a three phase motor with two leads hooked to a single phase line then all three to the equipment. Because I didn't have the caps or relays I had to turn on the power then manually turn the shaft to start it. Once it was running no problems that I could see. I used it to run my lathe, which didn't require a lot of power.

Meep-Meep · Dec 20, 2011

Oh, by the way, nice effort on your converter. Sort of the "stealth" model I suppose.

Budnicks · Dec 22, 2011

brandon64 that is a very cool self made phase converter....

astjp2 · Oct 28, 2012

I need to do something like this, machinery is so much cheapter in 3 phase. Tim

747mopar · Nov 9, 2012

Way to go, looks good. We had to do the same to run our lathes, mills, etc.

67 B-body · Nov 10, 2012

Gosh,,, this brings back memories!
My Cousins Dad established "American Armature" Electric motor reman company, and also started up another company called "Ameri-Phase" corp. that designed and built Phase Converters. I worked there for a couple years before heading into Robotics.
They were typically larger units that were shipped to Alaska for the oil rigs and such, but sometimes farmers would come in and purchase one for the farm.
Ours were single heavy duty Baldor 3 phase motors with the motors shaft cut flush to the front bearing, and a bank of capacitors housed in a metal box that was attached to the top of the motor. Insulated 3 Lug posts were available "housed" within the box for termination points for the 3 phase output. This did require a bit of rewire though....

gkent · Dec 4, 2012

Why build one when you can buy a decent electronic 3 phase converter for around $80. ?!?!?

Cranky · Dec 4, 2012

Stanton said:
Why build one when you can buy a decent electronic 3 phase converter for around $80. ?!?!?

What you're talking about is a static phase converter. Last time I checked into those, there was a lot of difference between the legs. The rotaries have the static converters beat hands down.....at least the last time I checked into them. They all need to be checked for equal output but the statics were usually the worse offenders.

Building a rotary 3 phase converter

brandon64

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Cranky

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Meep-Meep

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Cranky

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