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  • VFD instead of rotary?

    Hi guys, need to draw on the experience of the group once again.

    I have a Bridgeport Interact I CNC mill that currently uses a rotary phase convertor to convert my 220V single to 3 phase. My experience and what I've learned on line says the control is very sensitive to the 3 phase power it receives.

    I would love to get rid of my hot, noisy, power hungry rotary and go with a VFD like below:

    http://dealerselectric.com/item.asp?PID=4541

    Would something like this VFD create clean enough 3 phase and allow me to replace my RPC?

    Thanks!
    Andy

  • #2
    Won't work unless........

    A VFD is intended to run only one motor at a time with no motor controls down stream from the VFD

    If you are only running the spindle motor off your rotary you will be okay. And, the control and servos, etc can run off a 110V wall plug. Many CNC's are this way.

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    • #3
      Andy, you don't say how comfortable you are doing your own wiring ?

      What can be done is to rewire the input (220V) so that the "control" and "servo drive" portions run on single phase, which they do anyway.
      That moves the sensitive portion of the mill into your normal smooth electrical service.
      Then rewire the motor contactors ( F & R) to be the low power switches for the VFD.
      That puts the spindle motor (only) under VFD control , a far smoother operation.

      I am not a fan of Teco's, even though I have one on my Bridgeport manual mill...too much noise !
      I prefer Hatachi's..great units.

      Rich
      Last edited by Rich Carlstedt; 11-29-2012, 10:14 AM.

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      • #4
        DR brings up a good point. Your control system may only need 120 volts.
        The problem then however is the need for two switches (220 & 110 )- depends on your power panel

        Rich

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        • #5
          I'm fairly comfortable with wiring but at that point it's probably easier to just keep running with the rotary.

          I keep waiting for the control to die but it keep chugging along.

          Someday I imagine I'll have to do a retrofit but for now it keeps working so I keep using it.

          Thanks for the info guys.

          Andy

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          • #6
            Originally posted by DR View Post
            A VFD is intended to run only one motor at a time with no motor controls down stream from the VFD.
            That used to be true with the older VFDs. Many of the modern designs can be used with multiple loads.

            Have a look at this article from automation.com (linked from the Yaskawa site); http://www.yaskawa.com/site/dmdrive.nsf/536df907f9fe9d5586256c4e0056b851/86256ec30069e4328625787e00546dd9/$FILE/PR.AC.02.pdf

            The control may very well be fed from a single 110/220 phase, but the Servo supply is nearly always three phase as it's quite a large load and rectified 3 phase only has 33% ripple prior to smoothing compared to 100% for single phase. That doesn't mean you cant build a single phase servo supply, or even feed the existing supply from a second VFD.
            Paul Compton
            www.morini-mania.co.uk
            http://www.youtube.com/user/EVguru

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            • #7
              Originally posted by hitnmiss View Post
              I have a Bridgeport Interact I CNC mill that currently uses a rotary phase convertor to convert my 220V single to 3 phase. My experience and what I've learned on line says the control is very sensitive to the 3 phase power it receives.
              With a RPC your control should be on the two single phase (240v) legs, these are passed through without any change by the RPC.
              It is when you use one and the generated leg there is a problem.
              But I also say the VFD is the way to go!.
              Max.

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              • #8
                Just a point about your question - a VFD will generate much more balanced 3 phase than a rotary. I would just get one rated to handle multiple loads and switching.

                Comment


                • #9
                  You should still still isolate all the non-motor stuff from the vfd. No matter what a vfd "can" handle, it's designed for direct connection to A motor. Multiple motors can be handled on some vfd but there are many contraints. And if you want to run multiple motors forget using sensorless vector, braking etc. etc.

                  One dedicated vfd for the spindle using adjustable frequency and with braking; run the rest from single phase if applicable (often is). My Anilam 3 axis Millpwr BP is set up this way. The servos do not use 3 phase.

                  If you're really serious about good 3 phase power, buy the likes of a Phase Perfect. I have a 10hp (30 amp 240v) model for general 3 phase power. A vfd is not a replacement for an RPC. A Phase Perfect type system is an rpc replacement.
                  Last edited by lakeside53; 11-29-2012, 04:32 PM.

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                  • #10
                    Originally posted by EVguru View Post
                    That used to be true with the older VFDs. Many of the modern designs can be used with multiple loads.

                    Have a look at this article from automation.com (linked from the Yaskawa site); http://www.yaskawa.com/site/dmdrive.nsf/536df907f9fe9d5586256c4e0056b851/86256ec30069e4328625787e00546dd9/$FILE/PR.AC.02.pdf

                    The control may very well be fed from a single 110/220 phase, but the Servo supply is nearly always three phase as it's quite a large load and rectified 3 phase only has 33% ripple prior to smoothing compared to 100% for single phase. That doesn't mean you cant build a single phase servo supply, or even feed the existing supply from a second VFD.
                    Paul,

                    I have three CNC machines, all factory made, with 120V single phase servo supplies. The largest one has 40 in/lb servos and it can run all three at the same time. I was surprised by this. I thought the supply voltage would be at least 230V 1 phase.

                    I have no experience with machines with larger servos, and would expect their power needs would exceed the 120V supplies on my machines.

                    I do have an Austrian CNC lathe running off 380V three phase. I've never had need to study the servo supply there, it's much more integrated than the distinct supplies on the other machines and it may well use three phase. But, the axis motors are smaller than my others.

                    Comment


                    • #11
                      That article says:

                      Multiple conditions must be met when applying one VFD for control of multiple motors. First, each motor must have the same desired operating speed. With one VFD per motor, each motor can be controlled separately and run at a different speed. This is not so when running multiple motors from one VFD.

                      Which doesn't sound very practical for the application under discussion, or for machine tools in general.

                      Phil

                      Originally posted by EVguru View Post
                      That used to be true with the older VFDs. Many of the modern designs can be used with multiple loads.

                      Have a look at this article from automation.com (linked from the Yaskawa site); http://www.yaskawa.com/site/dmdrive.nsf/536df907f9fe9d5586256c4e0056b851/86256ec30069e4328625787e00546dd9/$FILE/PR.AC.02.pdf

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