RPC safe/acceptable imbalances?
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    Default RPC safe/acceptable imbalances?

    The single phase leg to leg voltage at my panel is 246V.

    I got my 25HP rotary phase converter (RPC) running. I have a 30KVA transformer hooked up to it to get 400V 3ph to drive my German CNC lathe. I want to use both the low voltage 230V side and the high voltage 400V side.
    At my old place, I was getting about 415V leg to leg or so on the high voltage side. At my house, Iím getting about 430V-440V leg to leg on the HV side, without any load.


    Now, on the low voltage side, I read 265V, 256V and 242V leg to leg, without any load.

    265V and 256V seem a little on the high side for me.
    Iím wondering what an acceptable voltage range would be that wonít hurt my machines (Mighty Comet VMC 10HP spindle, Webb/Whacheon WL-435 lathe 5HP spindle, Boyar-Schultz surface grinder, pedestal grinder, ...)

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    The US standards are +- 10% of nominal. Not sure what the German's use. I take it there are no taps on the transformer to adjust. Therefore, the best solution is to use buck/boost transformers to get where you want to go.

    Tom

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    Default RPC safe/acceptable imbalances?

    Quote Originally Posted by TDegenhart View Post
    The US standards are +- 10% of nominal. Not sure what the German's use. I take it there are no taps on the transformer to adjust. Therefore, the best solution is to use buck/boost transformers to get where you want to go.

    Tom
    Thanks for your response!
    The transformer does have taps, so I can adjust the high voltage side.
    I guess Iím more concerned about the low voltage side.
    Iím probably being a bit of a worry wort.

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    Quote Originally Posted by rpseguin View Post
    Now, on the low voltage side, I read 265V, 256V and 242V leg to leg, without any load.

    265V and 256V seem a little on the high side for me.
    With any load I get as high as 288Vac. But when the load starts the balance is within 2-3 Vac. That's what counts.

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    Quote Originally Posted by rpseguin View Post
    The single phase leg to leg voltage at my panel is 246V.

    I got my 25HP rotary phase converter (RPC) running. I have a 30KVA transformer hooked up to it to get 400V 3ph to drive my German CNC lathe. I want to use both the low voltage 230V side and the high voltage 400V side.
    At my old place, I was getting about 415V leg to leg or so on the high voltage side. At my house, I’m getting about 430V-440V leg to leg on the HV side, without any load.


    Now, on the low voltage side, I read 265V, 256V and 242V leg to leg, without any load.

    265V and 256V seem a little on the high side for me.
    I’m wondering what an acceptable voltage range would be that won’t hurt my machines (Mighty Comet VMC 10HP spindle, Webb/Whacheon WL-435 lathe 5HP spindle, Boyar-Schultz surface grinder, pedestal grinder, ...)
    Resistive dummy loads are easy to hasty-rig as tests, but... won't "tell the truth" vs inductive/motor loads.

    I'd use the 5 HP Wacheon as initial test load, set meters on all legs, it. Leave them there as you run some cuts, eyeball them whilst on power-feed..

    It is almost certainly the ruggedest machine in your shortlist with enough draw to matter.

    Balance the caps, and/or adjust the taps 'til it comes good, THEN try your CNC, also with meters in-place. Cheap ones will do, so long as they and their leads are good for it.

    You aren't fussed over anything more "fine grained" than about +/- 5 Volts difference. steady running, light or heavy.

    Might want to make sure nothing changes significantly if/as/when the load machine does something that presents a dramatic change. As CNC are wont to do - unless specifically commanded to tippy-toe about with extra stealth!



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