To VFD or Rotary Phase converter

General Discussion

  1. Blind Squirrel

    Blind Squirrel Well-Known Member

    Messages:
    1,124
    Likes Received:
    1096
    Joined:
    Oct 1, 2015
    Location:
    Pacific NW
    Local Time:
    6:09 AM
    I've been running my Bridgeport mill with a VFD for years and never a problem. I recently acquired a larger lathe to replace my bench lathe. This is also 220v 3 phase machine like the Bridgeport but a little larger motor. Also operates on 220v 3 phase. I could go with another larger VFD for the lathe or just switch everything over to a rotary phase converter set up. Any experience out there to help me lean one way over the other?

    If I go VFD I have to go larger anyway or it will push the operating limits of the one I have. The one I have is only rated to 2hp which the mill is (but never pushed that hard). Also, it's a one person operation and only one machine is in use at a time.
     
  2. Keystone

    Keystone Well-Known Member

    Messages:
    223
    Likes Received:
    289
    Joined:
    Dec 16, 2016
    Location:
    Central PA
    Local Time:
    7:09 AM
    I've never used the rotary phase converter setup, so I can't comment on that. I put a VFD on the mill I bought a few years ago and it's worked beautifully. They've become very inexpensive and just seems like the easiest way to go.

    If I'm understanding right, you're considering paralleling both motors off one drive? Technically that's okay (think some sort of machine tool that runs two identical motors for some operation, where they always run together and at the same speed) but in your case you'll have to install a disconnect between the drive and each motor, and then remember to jockey them on and off depending on which tool you want to run. I guess if you accidentally leave one on and try to start the other tool the drive would detect the overload condition and fault out. Still it's kind of a hokey setup.
    As cheap as they are now, why not just buy a second VFD for your lathe? I went with KB Electronics for my mill. They have a 240V single phase input at 2HP for $238

    KBDF-27D - KB Electronics - AC Drives | Galco Industrial Electronics

    I put mine in a small enclosure and added a pilot light so I'd know if I had the power on:
    20190808_163128.jpg

    drive box.PNG
     
  3. DesertRat

    DesertRat Well-Known Member

    Messages:
    3,144
    Likes Received:
    2803
    Joined:
    Jan 22, 2005
    Location:
    Moses Lake, Washington
    Local Time:
    4:09 AM
    I deal with VFDs as part of my job. Yaskawa has a nice converter/VFD combination that may be a solution for you. If you don't need the variable speed of a VFD a straight phase converter would be the better choice.
     
  4. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

    Messages:
    51,586
    Likes Received:
    20598
    Joined:
    Oct 14, 2010
    Location:
    Idaho
    Local Time:
    4:09 AM
    Why "switch both?"

    VFD's can be expensive, you can find used rotary converters the same way you find used machinery. Run one off the VFD the other off a rotary
     
  5. Dfr360cuda

    Dfr360cuda Diagnosis... Plum Crazy.

    Messages:
    1,866
    Likes Received:
    1245
    Joined:
    Aug 30, 2012
    Location:
    Finleyville, PA
    Local Time:
    7:09 AM
    Where I work, we've put in a lot of VFD's and LED lights lately. The company gets a tax credit.
     
    • Like Like x 1
    • Blind Squirrel

      Blind Squirrel Well-Known Member

      Messages:
      1,124
      Likes Received:
      1096
      Joined:
      Oct 1, 2015
      Location:
      Pacific NW
      Local Time:
      6:09 AM
      So I should further explain. At least some of what I understand. The mill is a manual mill and the VFD really only controls the motor. With the lathe. There are several electronic controls and the coolant pump (also 3 phase) to operate. Which if I infer from the information I've read. Leads to the best choice as being the RPC. But I'm unsure.
       
    • DesertRat

      DesertRat Well-Known Member

      Messages:
      3,144
      Likes Received:
      2803
      Joined:
      Jan 22, 2005
      Location:
      Moses Lake, Washington
      Local Time:
      4:09 AM
      They make RPC's and they make static phase converters as well. You should have no trouble finding the best fit for your needs. You will have to size it for the total load of all the motors on you lathe.
       
    • bcschief

      bcschief Well-Known Member

      Messages:
      1,312
      Likes Received:
      1027
      Joined:
      Feb 23, 2010
      Location:
      Crescent City Florida
      Local Time:
      7:09 AM
    • Keystone

      Keystone Well-Known Member

      Messages:
      223
      Likes Received:
      289
      Joined:
      Dec 16, 2016
      Location:
      Central PA
      Local Time:
      7:09 AM
      Thanks for adding the extra info. Basically what the Variable Frequency Drives are designed to do is run a 3 phase motor of pre-determined size at either a fixed or variable speed. Because they use output transistors to create a synthetic 3 phase power, they can also provide a 3-phase output when powered by single phase input power. That's the upside to them, the downside is that those transistors don't like being energized with no load. In other words, they're NOT like a transformer, where you can have power applied to the primary (input) side and anywhere from full load to absolutely nothing applied to the secondary (output) side.

      So with the additional components that need to be powered, a VFD probably isn't the easiest solution. I'm guessing the lathe's electronic controls will be coming off a transformer which will only need 2 legs of the 3-phase, so that you would wire to the power you're feeding the VFD with and not the output from it. The coolant pump is the tricky part. It will be cycling on and off and will provide an additional load to the drive. It was also designed to work best at 60Hz, which defeats one of the advantages of the VFD, being able to change the frequency and thereby the speed of the motor.

      So the rotary phase convert is likely the best solution in this case. From what I know about them, they're more expensive but they provide the flexibility of powering all your equipment from one source.
       
    • 4spd340Swinger

      4spd340Swinger Well-Known Member

      Messages:
      155
      Likes Received:
      112
      Joined:
      Mar 29, 2019
      Location:
      Cincinnati, OH
      Local Time:
      7:09 AM
      There is a definite increased price for a 3 phase unit V.S. single phase however a small Allen Bradley Powerflex 4 or an ABB drive wont break the bank. I work in a Aviation plant so I install and work on these daily. As stated above you need to look at other items being fed from the source such as the pump.
       
    • gzig5

      gzig5 FABO Gold Member FABO Gold Member

      Messages:
      1,938
      Likes Received:
      2258
      Joined:
      May 3, 2018
      Location:
      Mequon, WI
      Local Time:
      6:09 AM
      I’ve built two rotary converters, a 5hp in garage for the mill and 3 hp in basement for EMCO lathe . I have a total of maybe $100 in both including the motors, relays for starting, and balance/run caps. The lathe had a two speed motor and it wouldn’t work well with a vfd. Vfd is great for speed control but one rotary can run a whole shop.
       
      • Like Like x 1
      • Blind Squirrel

        Blind Squirrel Well-Known Member

        Messages:
        1,124
        Likes Received:
        1096
        Joined:
        Oct 1, 2015
        Location:
        Pacific NW
        Local Time:
        6:09 AM
        Looks like I'll be buying/building a Rotary converter. I completely forgot about the two speed motor. It wasn't the direction I really wanted to go. I have the VFD on the mill and it has worked flawlessly. I would have liked using one on the lathe also but it just doesn't seem to be the best choice. Well, I like new adventures. Thank you everyone for the inputs. Off we go!!!
         
      • gzig5

        gzig5 FABO Gold Member FABO Gold Member

        Messages:
        1,938
        Likes Received:
        2258
        Joined:
        May 3, 2018
        Location:
        Mequon, WI
        Local Time:
        6:09 AM
        You might be able to use the two-speed with a VFD by wiring in only the high speed winding. The way mine is wired to the multi-function switch, that wouldn't have worked too well. If you have any questions on the RPC, let me know. You can go simple with a rope pull start, or a little more complex with push button start and load balance caps.
         
      1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
        By continuing to use this site, you are consenting to our use of cookies.