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Static phase converter for running two motors?

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  • Static phase converter for running two motors?

    I am finally finished with what I would call the first phase of restoring/facelifting this Reid 2B surface grinder. I got all the black grease and grinding dust out of nearly everywhere- certainly everywhere that matters. It's put back together, painted, re-lubricated, rotting cables are replaced and I fixed the part I broke

    I made the mistake, however, of testing the motors with the same VFD. This machine has power cross feed operated by a separate motor that Reid instructs you to switch on only after the spindle motor is on. The manual says if the table moves the wrong way at first to switch any two wires of the crossfeed's motor ( both motors are 3 phase). It was going the wrong way at first, so I switched L1 and L2. now the crossfeed motor only hums when powered and a multimeter test gives me no continuity between L1 and the other two phases. L2 and L3 passed the test. I will take the motor in to be rewound.

    Going forward though, I figure I ought to not try powering this machine with a VFD- because of the whole business of starting the power feed motor only after the spindle motor is going. I have to start the spindle when the frequency on the VFD is around 17Hz. Too low and the magnetic starter won't make contact, too high and the VFD will over current and shut off. Of course, once it's running I dial it up to 60 Hz.
    I don't have 3 phase in my shop, although I do have 240v. Am I better off going with a static Phase converter instead? I think a rotary phase converter is too expensive so long as there are other options.
    Attached Files

  • #2
    My mistake, thought I read static converter....
    Last edited by reggie_obe; 06-23-2022, 09:48 AM.

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    • #3
      It's a bit confusing with what you are saying , or i don't understand the setup
      You say you must be over 17 hertz to get the contactor to engage... STOP !
      You don't want contactors after a VFD , They must be before !
      And if the VFD drops out, it is too small for the setup.
      Yes, A static Phase convertor can run two motors by having the running caps on the motor and using the starting cap in the front of the circut
      Rich
      Green Bay, WI

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      • #4
        I am running both my lathe and mill on a WNY static converter. The converter is configured for the 2 hp mill. When I want to run the 1 hp lathe, I disengage the spindle on the mill and turn it on. It then functions as an RPC for the lathe. Been running that way for over 4 years.

        https://phaseconverterusa.com/Static...rter_c_11.html
        It's all mind over matter.
        If you don't mind, it don't matter.

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        • #5
          Thanks rich, maybe i am calling something a magnetic contactor when it's something else, I 'all put a picture up. The same setup is how i run the motor on my mill. In fact i borrowed the vfd from my mill to test the grinder. I have the cable that would normally go to a 3 phase outlet go to the vfd instead. That way i can still use the machine's original switches. I get the frenqency up to about 17, hit the start button and then turn. The vfd's frequency up to 60. I figure this is how it should be done but maybe the more knowledgeable of you here can point me in the right direction.
          Moreover, i looked again at prices on the controller only on rotary phase converters and it's not as bad as I thought. I might get a controller and used 3 phase motor. but is running a 3 phase motor on single phase ( like a static phase converter does) damage the motor after a while?

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          • #6
            There's the picture of what I think are the magnetic contactors.
            Attached Files

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            • #7
              Tillie, do one of the following:
              1. Get/build a RPC.
              2. Oversize the VFD by a lot. (Can't recommend in good faith though it works and dad's been doing this for years.)
              3. Ditch the contactor for the the spindle motor, ramp that with the VFD, then hard start the table motor. (Can't recommend in good faith though it works and dad's been doing this for years.)
              4. Separate VFDs.

              Please don't use "static" boxes for anything, ever, other than starting an RPC motor.

              Remember that VDFs weren't originally built as phase converters. They were devices to provide solid-state one-off, soft start, and speed control. It just so happens that by design of the DC conversion, some can tolerate single phase input. Therefore the VFD was designed to replace all switching and circuitry downstream of it.
              Last edited by The Metal Butcher; 06-23-2022, 02:29 PM.
              21" Royersford Excelsior CamelBack Drillpress Restoration
              1943 Sidney 16x54 Lathe Restoration

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              • #8
                Yes I'm leaning toward a RPC the more I think about it.

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                • #9
                  Change the Line leads around. The control doesn’t like being powered by the false leg.

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                  • #10
                    Originally posted by no704 View Post
                    Change the Line leads around. The control doesn’t like being powered by the false leg.
                    There is no false legs on a VFD.
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

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                    • #11
                      And they are not "false" on an RPC.... It's the "generated" leg, or "manufactured" leg. Just as real as any other, but not as much power behind it as the straight through legs.
                      CNC machines only go through the motions

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