The Home Machinist!

Upgraded my RPC from 3hp idler to 20hp idler(with pony motor, no pull rope starting this one) to handle the 5hp lathe motor. I got a transformer off of eBay but ran into probs with outcoming voltage. Getting 435, 489, and 490 volts. I've tried everything but they stay the same. I've been talking to Mike Kilroy and he suggested that if I wanted to keep the transformer (which would cost more to replace with S&H prices) to find a couple Buck/Boost transformers to lower the high legs. I can start the lathe with the voltage the way it is but I don't want to run it long with the 2 high legs.
I got this lathe for free ( just had to go to St.Louis to pick it up) so I'm pretty excited about actually working with it. Just seeing it run makes me want to dive right in and get to it.

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Tim Lewis
Paxton, Illinois

Sorry I can't help you with the technical problems, my electrical skills are about exhausted installing a breaker. However, many peole on the forum would probably enjoy seeing pictures of this lathe, and would like to hear the story of you acquisition, so I so have a suggestion: pictures & story.

--Bob

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--Bob

Gorton NC mill converted to manual to be converted to CNC.

viewtopic.php?f=42&t=92542&hilit=catman81056
Here it is in a nutshell, I've painted a few of the bottom panels and made a new end for the auto carriage stop. I've been putting it off till I knew for sure it ran, so I'll be hitting it hard now.

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Tim Lewis
Paxton, Illinois

Unless your RPC setup is of a configuration I am not familiar with, the common cause of a high voltage is too much capacitance. Also, because of the pecularities of the 3 phase symptom, your readings indicate only one leg, almost surely the "generated" leg, is actually high. I am assuming your readings are leg-to-leg. When one leg is high it causes the voltages from itself to either of the other two legs to be high. The fact that both of your high readings are nearly identical indicates that the phase angle of the generated leg is correct, so capacitance may not be the problem.

You say you have tried everything, did that include switching the motor and transformer leads around? Is the same unbalance present directly at the converter output, with and without the transformer connected? I would guess that you may have some unbalanced windings. The situation might improve under load but an unloaded 5HP motor is unlikely to have much effect on a 20HP converter. It might help in troubleshooting to know whether your transformer primary and secondary are delta or wye connected.

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Don Young

Coming out of the RPC I have 220,221.242 volts, there are no capacitors. I have tried switching the incoming and outgoing lines around at the transformer. All incoming lines are wired with the #3 tap which should produce 436volts. I tried using the #2 tap on 1 line and the voltage went up to 510 volts. I called Acme and the guy said to take reading while the lathe was running, I did and there was no change.
I'll give the buck/boost transformer a try.

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Tim Lewis
Paxton, Illinois

Just a thought: you might try a single bucking transformer in the single phase 240V line. Your voltages out of the RPC seem pretty normal, with the generated leg a bit lower causing two of your voltages to be a bit low. Your transformer must be connected in a wye-delta or delta-wye configuration to switch from one low leg to one high leg. I will try to figure out just how that can happen. Maybe someone else knows and will post some new ideas here.

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Don Young

Not excactly a new idea..I enhanced the spec plate to see the main drive motor was origionally stamped 440v-3ph and then it looks like a "2" was stamped over it, to read 240v... Ok fine. Further the coolant pump mtr is 440v-3 but the "control" motor is 220v-1ph. The control ckt is of course 110v-1. It seems like, instead of various xformers and different power supplies, this layout extracted some phases directly out of the drive motor to drive the control motor which is probably the VS already there. Then that would feed back to control the drive motor. A real schemo and a guy like Webb would find this a challenge over lunch. Sorry for no direct assist