thanks to everyone for your thoughts!
Many pictures and the story in several chapters:
MAIN PAGE
This text details how I made a 10 horsepower rotary phase converter from $45 worth of parts that I bought from an industrial junkyard gloriously called Pioneer Industrial Services.
At some point, after reading rec.crafts.metalworking and this excellent article on making homemade phase converters, I became excited about the idea of making a rotary phase converter from second hand parts.
I spent about an hour calling around and finally found a guy Dave from Pioneer Industrial Services, who said that he had used 3 phase motors. He has a junkyard full of used electrical components. Here's what I bought, and for how much.
The nice surprise was that the 10 HP motor was possible for me to manhandle alone.
My first prototype was a simple setup with no switch at all, I simply touched the wires to the 240V pieces of the subpanel. Click here to see and read about the first prototype. It sucked and took a long time to spin up, due to poor contacts. It was atrocious.
My second prototype included installation of a 50 amp circuit breaker into the panel, hard wiring of the wires to the breaker, and use of a Definite Purpose Contactor and a regular lamp switch to turn the contactor on. Click here to see and read about the second prototype. This works great, but is ugly and unfinished.
My future plans nclude making a nice carriage on little wheels for the converter, and hiding all electricals inside safely.
WHAT I BOUGHT
I bought the following:
- 10 HP 3 phase Century motor - . * 7.5 HP US Electrical Motors 3 phase motor - . I bought it just in case. * 30A heavy duty Square D single throw switch - . * 50A Definite Purpose 3 wire normally open relay - . * Five 535 V 92 mF capacitors the size of a vodka bottle - for all ( each).
Dave from Pioneer Industrial Services is highly recommended, he is friendly and his proces are reasonable. I was able to pick everything that I needed, from him. He is in Addison, IL.
FIRST PROTOTYPE
The very first try was quite simple. I spun the motor by hand and then applied power. No capacitors. The motor was finally able to accelerate, after much difficulty. That proved to me that it was not "fried".
My first prototype was simply a test of the concept -- would a three phase motor spin up like they say, if I apply capacitance between one power leg and the generated leg?
I wired the motor as follows: two legs of 240V were connected to the two legs of the motor. These I call Leg 1 and Leg 2. Leg 3 was connected to Leg 1 via three capacitors wirted in parallel. You can see that on pictures.
That made the motor spin up reliably, but slowly due to very poor contact between my wires and the subpanel. After that, I decided to try better wiring. See next chapter.
SECOND PROTOTYPE
Since the concept obviously worked, I now wanted to go a little bit farther and wire it more properly.
I wired it as follows. I installed a 50 A crcuit breaker in the subpanel. I hard wired the 8 gauge wires with one end into the breaker, and another into the 3 pole definite purpose contactor.
The contactor is a neat thing that, when 110 V is applied to two sensing contacts, with very little current drawn from 110v it closes the big contacts for all three poles.
Legs 1 and 2 of utility 240V were connected to legs 1 and 2 of the motor. Leg 1 (on the motor side, not on utility side) was ALSO connected to one side of the capacitor bank. Leg 3 (the wild, generated leg) of the 3 phase motor was connected to the other side of the capacitor bank. That's how self starting phase converters should be wired according to this excellent article on making homemade phase converters
The converter now would spin up in less than a second. My next task was to measure voltages between legs, which would be suggestive of the actual degree of phase shift. The voltages were as follows: 256 V utility, 239V, and 271V. I did not like it.
I then removed one 92 mF capacitor from the bank, leaving only two capacitors with the total capacitance of 184 mF. The effect of this was that instead of less than a second, the motor would spin up in about one second. Not a big deal to me. The voltages now were as follows: 256 V utility, 240V, and 260V. I decided that I should go with two capacitors.
Costs of parts actually used, so far:
- 10 HP motor -- * Definite Purpose contactor -- * 2 capacitors, 92 mF each --
The total cost, so far, is $45. Wires and new breaker do not count.