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  • #31
    If you change motors I'd like to buy your 3 phase. Please let me know as soon as you decide. Thanks! Eric

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    • #32
      Originally posted by PixMan
      What do you mean by this?

      A Phase Perfect Digital Phase Converter is no laughing matter in price or performance. Full power, perfectly balanced phase and voltage, and dead quiet. They are anything but cheap but if you're trying to power-up a 1990's vintage CNC mill or lathe such as I anticipate doing, a Phase Perfect DPC is the closest thing to incoming 3-phase, and probably cleaner.

      http://www.phaseperfect.com/

      Do you mean you have purchased and installed one of their products? If you have one of these, why spend even more money on 3-phase VFD's? I can see where some speed control on some machines would be nice, but it sounds like you'll be spending beaucoup bucks on power supply stuff. I try to spend it on tooling and machines.


      yes, I just purchased and installed one (blue box to the left). 10hp unit for $1500 from CL - about half price. It currently runs my lathe and compressor, and a few extra outlets for whatever.






      VFD's offer much more than three phase conversion. Soft start, rated motor starter (over current protection) etc etc. and... single phase vfds over 3 hp get expensive. 3 phase means I can buy cheap surplus vfds. Industry seldom buys used vfds; homeshops rarely have 3 phase


      I'm about to intall a 240->480- transformer to take advantage of even cheaper vfd's
      Last edited by lakeside53; 08-21-2011, 10:26 PM.

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      • #33
        Originally posted by MichaelP
        You'll need a separate one for each machine. Sorry!

        Lakeside53,

        Thank you for the very interesting link.

        Now, some measurements and calculations demonstrate that my 3-phase RPC-based line, when fully unloaded, is 3.4% unbalanced. This is only slightly above the recommended 3% max. for the utility lines, but well below the 5% max. permitted by Nema MG-1 for motors.

        As soon as I turn on one of my machines, the unbalance drops to 1.8-2%. Based on the table presented in the article, I can derate my motor to about 95-97% of its full capacity to be very safe. And it's not because the motor loses power, but in order to keep it at specs at full power (in terms of heat). Anything to avoid an extra 10% of temperature rise if I decide to take the motor to its limit.

        How often, if ever, we operate our motors at their full capacity is, really, a rhetorical question.

        You are one of the lucky owners then; good, you can sleep at night You can even run cnc from that. Most rpcs I measure are far from balanced, and the owners are safely oblivious. In addition, most equipment I see in the home ship doesn't have over current protection for the motors, so I guess that they don't know won't hurt them Must be true, because few homeshops actually burn out motors.
        Last edited by lakeside53; 08-21-2011, 10:27 PM.

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        • #34
          My electrical skills and understanding could fit on the head of a very small pin, But after seeing what a 3 phase motor VFD combination can do on my mill I'd never go back to single phase. Smoothness of opereration, Soft start, Programable ramp up/down, Variable speeds ect. In fact I plan to change my single phase lathe motor over to a 3 phase VFD set up. Forrest's point about not getting too far away from the motors normal operating range is of course 100% correct. Everyones needs and wants are different, But for 99% of us here I think that a VFD is the way to go.

          Pete

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