3 phase question

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Yeah I know, dipping into troubled waters with all these electrical questions...

I was taking with one of my Massage Therapist's (that nagging shoulder injuruy is still with me) who is also a lover of old tools. He was saying he drove an old 3 phase tablesaw by using 2-3 phase motors, and a single phase motor.

He could not remember exactly how the old set up was, but somehow the single phase motor powered the extra leg of the 3 phase motor, then that 3 phase motor powered up the tablesaw. He even said that he could shut the mid-3 phase motor off at some point and just use the single phase and the 3 phase tablesaw motor to power his saw.

Like railroad motors, 3 phase motors are easy to be had in the industrialized world of machine shops in which I work. All this sounded good to me, but I kind of wondered if he was remembering this set up correctly. I never heard of using a single phase as a 3 phase converter.
 
I have no idea what he is talking about. I have a RPC I built. Rotary Phase Converter.

In a nut shell I hit the start button. Single phase power is sent to the idler motor (a 15 hp 3 phase motor) and the 3rd leg/phase is sent to the idler motor via a set of run capacitors in the enclosure. That starts the 3 phase motor.

Once it is started a relay cuts out and the motor runs on the single phase. 3 phase motors won't start on 2 hot legs but they will run on it once spinning.

With the idler running the panel now sends single phase power out the supply lines to my 3 phase machines. The idler motors 3rd leg, that is now not powered is now operating as a generator. It generates/provides the 3rd leg of the 3 phase to the 3 phase machines in my shop.

My panel is not a simple panel but it is one of the best designs I have seen. Works perfectly and I love having the 3 phase option.
 
Pssssssssst...... Alan............

We go to Costco all the time!

Got a flat of NICE Florida Navel Oranges and Aussie Beef steaks that are SOOOOO good :thumb:

Had Sushi for lunch today as well :D :wave:

Not to mention CUBAN cigars! :thumb:
 
Travis, what he was probably recalling was using a single phase pony motor to get a 3 phase idler running (instead of start caps). The idler then provides the 3rd phase for the motor you want to run. If that motor is too big for the single idler, you can use two or three to make up the needed capacity. Without run caps to balance between the 3rd phase and the single phase 220, the actual power factor is somewhat less than what you get with "pure" 3 phase, but the machine still runs well enough to use.
 
Some people use a single phase "pony motor" connected to the 3 phase idler with belt and pulleys to literally spin the 3 phase motor up to speed and then (I assume) apply single phase power to the idler once it is spinning and disengage the "Pony" motor. I think that is what John was referring to. I have never seen one or the diagrams but the theory make sense.

Bruce Norton, who designed my panel, told me he was working on the designing a panel for use with Pony motors. His panels are very well designed but they over the heads of most people without some electrical background. So he has been looking for something simpler and he was thinking that the pony motor might be a good choice.

IMO, Bruce has the best design I have seen. He incorporates motor overloads and fuses everything in his panels. While not the cheapest to build I think it one of the safest panels out there. And Bruce freely shares his designs.
 
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Sorry I wasn't more clear, Jeff's got it right. The single phase motor is used to spin up the first 3 phase idler, then single phase power will keep the idler going. The pony motor is sometimes connected via a belt with a de-tensioning device, though I've also seen them with just a rubber tire that is held against the spindle of the idler motor and put aside when finished (safety first! :rofl:). Start capacitors are a much better way of doing these things.
 
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