No amps on RPC

[James Boster]

I built my owm rotary phase converter about a year ago and have been running several machines without any problems. They start ok, dont heat up, have plenty of power, etc. I know that when I built mine I should have checked the voltages on the three lines but never did. Last week I helped a friend build one for his shop. He checked the voltages on his and was preparing to balance them which we both understand how to do(I just never done it). When he checked his the voltages were about what we expected from all we've read. But when he checked the amps on both the line to converter and load line there were only amps on two lines, none on the third or wild leg. He came over last night and we checked mine, same story. On my 10hp converter voltages were 116,118,180. I know that should be better and I will balance them out, but when we checked for amps we got the same results, amps were what we would expect for the load on two lines but 0 on the wild or made up leg. Can anyone explain this?

[john whittaker]

James....Can't help you with your question...but wanted to bump you back up top since you haven't got an answer yet. Maybe some of the electrically savy folks will see it. Besides, I grew up on Sleep Hollow GC and couldn't resist helping a fellow hillbilly. And no...I'm not related to the lottery winner.

[Rick Christopherson]

Well you can thank John for the bump to this thread, I hadn't seen this before now.

First off, you cannot check voltages between phase and ground. The numbers you provided are meaningless in regard to balance of the converter. You need to check your phase-to-phase voltages for setting up a balanced converter.

With your phase-to-phase voltages, I can tell you how far out of balance your converter is. These numbers should be in the ballpark of 240-volts, not 120 volts.

Even though you didn't say this, I do need to ask because of the voltages you listed. You don't have a neutral connection in your converter do you? If you do have a neutral, then you need to rewire the converter, as there is a mistake in the design. If you were measuring a phase-to-neutral current, you should be getting nothing, as the motor is not using the neutral.

[Dave Mcintire]

What type of ammeter are you using and was the load motor under an actual load?

[James Boster]

First off John, thanks for helping a fellow "hillbilly" out, looks like it worked.

Second I did check the voltage from phase to phase and it was around 240, can't remember exactly but will check again tomorrow. I'm on midnight shift now.

Third, My converter is a 10hp motor and it runs my 24" powermatic planer. We started the planer 7 1/2 hp and the feed motor on it another 1 1/2 hp. It was running at an "idle" when we checked. After we unhooked meter we discussed that we should have planed a board to check under a load but it was getting late at that point. the meter was my friends, it was a new clamp on digital meter he purchased from Sears. I only have a cheaper analog type.

Thanks for any and all help.