Building a 3ph Rotary Converter

[nine4gmc]

I am considering building a rotary converter to run/test equipment at my shop. I have seen plenty of threads showing them and diagrams but some things are still not clear so I figured I would start a thread to help answer some questions.

I would like it to power a 1hp 3ph motor. I have several different 3ph motors as an idler, up to 1.5 hp, what is the best size?

What size capacitors and where is the best source?

What size 110 motor will I need to spin the idler?

How many circuits will I need to run to the converter? One for the 110v motor and two for the idler motor that in turn, powers the machine?

Any help appreciated.

 

[theoldwizard1]

I think your 1.5 hp 3p motor will be marginal. My guess is that you will need at least 2 hp maybe 3.

I have seen videos of people "rope starting" their idler, so I'm guessing you will only need about 1/2 hp.

The idler of course needs to be on a 240V circuit. The starter motor should be on its own 120V circuit.

Someone has to have an equation to figure out run capacitor sizing.

 

[larry_g]

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

Be aware that on the linked document you have to click on the blue "figure" words to get the picture or schematic to come up. I built the 5hp one 10+ years ago and it is still humming along. I used the caps recommended and the balance was good. I changed the control circuit to 24vdc as I had all the relays in 24vdc.


As far as needing a starter motor I would suggest that you try a rope start to begin with.

Balancing caps are a bit dependant on the load your driving and the capacity of the motor. If I had a selection of motors I would choose the older heavy framed one with the slowest rated speed, normally 1725 rpm.



lg
no neat sig line

 

[930dreamer]

I'd start with a 5 hp idler.

I haven't added any caps yet, I was given a case of used ones. I bought a handful of new ones from an internet salvage store, name isn't coming to me.

If you can build a good way to tension the belt between the two motors, it just needs to spin up to speed.

Circuits- regular 120v for the pony motor, 240v circuit for the idler.

If you were closer I'd give you an idler.

 

[kazlx]

Best money I've spent. Phase Craft on eBay. You can thank me later.

You will want to go with a 3HP minimum. I used a 5 for my BP.

http://www.ebay.com/itm/3-HP-ROTARY...817?pt=LH_DefaultDomain_0&hash=item43ad601429

 

[Cryptic1911]

Would it be easier to get a cheap vfd to do the job? they are reasonable on ebay

 

[kazlx]

I have both. When I move in the next couple years and do it again, I will get a 10HP+ idler and run 3 phase through my shop. Some people love VFDs, but I prefer to use the regular machine controls.

 

[saabman]

I am in the VFD camp. I run my CNC mill (3 HP) and drill press (2 HP) off dedicated VFDs.

 

[nine4gmc]

The main reason I want to build a rotary is I have most of the things on hand. I would need to buy capacitors but I think I have the relay already and I have several 3ph motors. If it will cost me $100 or more to build the rotary, I will just pay the extra and get a VFD.

 

[larry_g]

If it will cost me $100 or more to build the rotary, I will just pay the extra and get a VFD.

Be aware that VFD's are sized to a motor and then programmed for operating parameters. In your original post you stated for testing so that says to me that a VFD may not be the best choice if you are running machines of various horsepowers.

lg
no neat sig line

 

[bsaint]

I dont mind VFDs for simple motor controls, but after using them in my shop for different things, I would love to get rid of them for a 20 hp phase converter to run everything.

 

[kazlx]

I dont mind VFDs for simple motor controls, but after using them in my shop for different things, I would love to get rid of them for a 20 hp phase converter to run everything.

Agreed. For one or two things VFDs are easy. If you don't want to buy a VFD every time then an RPC is nice. You start looking at equipment different after you realize 3 phase is an option...

 

[gorilla]

A three phase converter does not need a pony motor to start it. You can use a capacitor to start the motor with a push button start button or a time out relay. Once its up to speed you will have the third leg. I've built three converters this way and still working after 10 years. You can use capacitors to better balance the generated leg if need be.

 

[lametec]

A three phase converter does not need a pony motor to start it.

Depends on the size of the idler motor. For a 5HP (or smaller) like this guy is looking at, no pony is needed.

My old, big and heavy 20HP however, you don't want to cap start. I use a 1.5HP pony to spin it up.

For size reference, we have 40HP motors here at work that are smaller than my 20HP!