# Wiring for home made rotary phase convertor



## jschance (Jan 27, 2013)

*Wiring Questions for home made rotary phase convertor*

I'm in the process of building a rotary phase convertor out of a 5hp 3 phase motor (I need to test out the motor on my SB Lathe), and I'm missing something.

What do I do with the neutral wire?  

I understand how I wire each leg of the 220v line to the 3 phase motor, and then feed the 3 phase with these two legs, plus the 'phantom' leg generated form the 3 phase motor, but where does the neutral wire come in?

Also, the lathe came with a 4 prong twist log plug.  I picked up a 4 lug socket at Menards, which wire goes to which lug?

Thanks for the help.


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## bcall2043 (Jan 27, 2013)

jschance said:


> I'm in the process of building a rotary phase convertor out of a 5hp 3 phase motor (I need to test out the motor on my SB Lathe), and I'm missing something.
> 
> What do I do with the neutral wire?
> 
> ...



I am no electrician nor have I played one on TV but I have found that “Ugly’s Electrical References” handbook is a good place to find a lot of the electrical answers if you take time to study the info there. It has all the wiring info for the different types of electrical plugs. The link here http://www.cooperindustries.com/con.../literature/lit_pdf/O-Technical Reference.pdf  was referenced in “Ugly’s” and should guide you through the wiring details.

The wiring supply to your rotary phase converter should have at least three wires going to it, two hot wires and a ground. If you need an 110V supply inside the phase converter (for relays or lights) you should use a four wire supply, two hot wires, a neutral, and a ground. *Note* that when using the three wire supply that the third wire is ground not a neutral. Always provide a correctly connected ground to your machines!

Coming out of your rotary phase converter you should have 4 wires. Three "hot" wires (two original supply hot wires and the "phantom") from the idler motor windings and a ground. These should be wired to match your machine plug which should be wired to your machine according to the NEMA wiring diagram configuration. 

Note that the plugs are "phase and current" specific by NEMA standards.

Hope this helps.

Benny
The Orphanage Never Closes

*EDIT - additional:*
I just assumed you had already built your rotary phase converter from plans you had gotten somewhere and were just asking questions about how to make the connections to your lathe. After seeing Richards post I thought "maybe not". There is more than just what I said. Let us know what you have connected up. As Richard mentions the phase converter can be rope-start or they can be self-start, simple or more complex! There are plenty of plans out there. I picked the self-start version when I built mine. A few more parts and work up front but easy push-a-bottom down the road.
Benny


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## Richard King (Jan 27, 2013)

My Dad  told me when he opened his shop in NE MPLS back in 1955, that area did not have 3 phase power and the power company showed him how to make a phase converter.  He said a few years later they brought in 3 phase to the area and he never hooked up, just used his home made phase converter.

Several years later at our cabin, we had a small shop and he made up another one.
Here is how he hooked it up.
He told me a simple formula for motor size is HP x 1 1/2:  If you have a 5 HP machine 3 /ph.  Buy a 7 1/2 HP 3 phase motor and

 Connect wire numbers 4,5,6 together and wrap with tape.
Connect 1 phase power from your electrical switch to the 3/ph motor to wires 1 and 7 and your 3 phase machine, tape up,
Connect the other 1 phase wire from your electrical switch to the 3 / ph motor to wires 2 and 8 and another 3 phase to your machine. Tape up.
Connect the 3 /ph motor wires 3 and 9 to the last 3 phase to your machine. 

He had a pulley on the motor shaft and used an old lawn mower rope to spin the motor and flip on the single phase power at the same time and away it went.

I have seen guys connect a 110 volt motor on the 3 phase motor to start it spinning and after it started to spin they would shut off the 110 motor and it would spin free, I guess there are a few other ways to do it too.  But that's how you can hook it up.


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## jschance (Jan 27, 2013)

OK, what I need to power up is a 1 1/2 hp 3 phase motor on a South Bend Lathe.

What I'm rigging up is a way to test to see if the motor is actually functional, then if it is I'm pretty sure I'm going to purchase a VFD as a permanent solution.

My proposed rig is I have a 5 hp 3 phase motor that I'm intending to use as an idler to convert my 220v single phase to 220v triple phase.

So if I follow what Richard directed: 

Connect wire numbers 4,5,6 together and wrap with tape.
Connect 1 phase power from your electrical switch to the 3/ph motor to wires 1 and 7 and your 3 phase machine, tape up,
Connect the other 1 phase wire from your electrical switch to the 3 / ph motor to wires 2 and 8 and another 3 phase to your machine. Tape up.
Connect the 3 /ph motor wires 3 and 9 to the last 3 phase to your machine. 

Do I hook the ground (3rd wire on the 220v single phase plug) up to the ground lug in the 3 phase motor's electrical box?

Oh, and I've set up a small 110v 'pony' motor to bring it up to speed before I turn on the 220v power.


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## bcall2043 (Jan 28, 2013)

jschance said:


> OK, what I need to power up is a 1 1/2 hp 3 phase motor on a South Bend Lathe.
> 
> What I'm rigging up is a way to test to see if the motor is actually functional, then if it is I'm pretty sure I'm going to purchase a VFD as a permanent solution.
> 
> ...


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## Richard King (Jan 28, 2013)

First of all, I'm no way an electrician,  but I have used a 3 phase 220/ 440 motor wired like that to to get 3 ph power in my shop at my cabin.     It is a simple method. I am sure there are better ways to do it.  But I only used it on rare occasions.  My Dad ran his for hours every day of the week...for years.   Good luck


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## jschance (Jan 31, 2013)

Success!!!

I was able to get my home brewed rotary phase convertor working last night and successfully powered up my SB Lathe.:drink2:

It's currently pretty ugly, but it's working. 

Thanks to all for the help.  Now to get a toolholder and start making some chips!


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