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  • Vfd or rotary phase converter

    I am wanting to hook up my monarch lathe equipped with a 7 1/2 hp motor. My Bridgeport is equipped with a vfd and that works great. I think it would be sweet on the lathe too.
    I have been offered a 20hp rotary phase converter for $750. It would give me room to grow.
    Help me decide.

  • #2
    If all you have for available power is single phase then you're going to have to double the inverter size...mucho shekels! I would grab the rotary at that price...a real steal. You won't get the added fluff that comes with the freq drive so you need to think about what matters the most... saving dough or bells & whistles.

    Stuart

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    • #3
      About 50% bigger on the VFD. He should be able to get away with a 10HP unit. Accel speeds can be adjusted if it trips any alarms.

      I would jump on a VFD over a RPC any day. VFDs run smoother and use a lot less power.

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      • #4
        The first question I have is which Monarch lathe and how are you powering it now? I know that some 10ee lathes were converted by Monarch to a 7.5HP three phase motor with the speed control replaced with a VFD. That combination needs real three phase power.

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        • #5
          It's a 14c, new to my shop so it hasn't been powered up yet. Stuart said a mouthful.

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          • #6
            Get that RPC, that is a good deal.
            Randy
            Do yourself a favor and see if your TV carrier has America One News Network (AONN). 208 on Uverse. It is good old fashion news, unlike the networks, with no hype, bias or other BS.

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            • #7
              Randy
              Check "Tinkering" as one HMSC member has made a static converter for his old motor generator unit.
              JRW

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              • #8
                Rotary draws a lot of amps for the larger sizes. Check that. VFD a good choice if the price works for you. I'd forget the static unit. If you plan on growing, Phase Perfect is the way to go. That's what I use and NO problems. Tough on the budget, but worth it depending on your overall needs.
                Toolznthings

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                • #9
                  Yep, +10 for the Phase perfect. 10hp unit (33 amps per phase) is less then $3k. I have one in my home shop and have never looked back. As it's just "like" utility power, you can run three phase vfds or whatever.
                  Last edited by lakeside53; 04-18-2014, 10:17 PM.

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                  • #10
                    Hands down, a VFD
                    You can buy a 10 HP Hitachi unit for less than 600
                    http://driveswarehouse.com/p-1384-sj200-075hfu.aspx

                    A 20 Rotary wastes too much power
                    Your consumption will be half with a VFD

                    Rich
                    Green Bay, WI

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                    • #11
                      Originally posted by Rich Carlstedt View Post
                      Hands down, a VFD
                      You can buy a 10 HP Hitachi unit for less than 600
                      http://driveswarehouse.com/p-1384-sj200-075hfu.aspx

                      A 20 Rotary wastes too much power
                      Your consumption will be half with a VFD

                      Rich
                      And you get dynamic braking. Just watch that if you have a threaded spindle. Been there, done that and almost had a chuck in my lap.

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                      • #12
                        [QUOTE=Rich Carlstedt;915661]Hands down, a VFD
                        You can buy a 10 HP Hitachi unit for less than 600
                        http://driveswarehouse.com/p-1384-sj200-075hfu.aspx/QUOTE]

                        Whoa Mr....this drive is not a single phase input...need many more shekels for that item. Don't quote me, but I would say a 15 hp unit would be required and they ain't cheeeep!

                        Stuart

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                        • #13
                          You can probably use it on single phase with about 50% derating, but officially only up to 3 HP 240V. Here are the specs:
                          http://driveswarehouse.com/documenta...chi/SJ200M.pdf
                          http://pauleschoen.com/pix/PM08_P76_P54.png
                          Paul , P S Technology, Inc. and MrTibbs
                          USA Maryland 21030

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                          • #14
                            Starting expensive and reducing from there...

                            1) The phase perfect is by far the highest dollar, and has the least benefit per $.... It gives you good 60Hz 3 phase power. End of story.

                            2) The VFD is the best function per $, but a full rated VFD for that power level will be expensive also.

                            Yes, you almost certainly WILL need to derate by about 50% if you want full power output. You can get by with a smaller unit if you program it to pretend it is a smaller unit, so a 7.5 HP programmed to pretend to be a 3.5 or 4HP unit or will limp along at half power. That may not be too bad, as long as you use long accel and decel times. At home, you likely will NOT be making a lot of 7.5HP cuts... could be fine, but might be pushing matters as far as being able to run the unit, since the motor will take most of the amps (but at low power) when just idling. I suspect you'd want at least 5HP worth of VFD, which means a 10HP programmed to be a 5HP.

                            3) The RPC will do for you exactly what the Phase Perfect does, at much less cost. The super duper output balance etc is not a big deal for a regular motor, especially one which won't be pushed hard for max production.

                            The losses in the RPC are not so horrible as to break the bank.... o idle it pulls current, but at a lousy power factor. You don't pay for power factor, just for watts, so that doesn't hurt you. If you feel bad, or want to minimize input current, you can put Power Factor correction capacitors on it.

                            That isn't a bad price.... unless you can find a motor and make your own RPC. There isn't much to them.

                            4) The static converter is the cheapest way in, and could actually work for you, since you have so much more power than you are likely to use. But you get none of the benefits of 3 phase power, other than the fact that the static converter will run your motor on single phase....

                            Actually it will START your motor on single phase... after that it needs to do nothing, as the 3 phase motor will run at reduced power on single phase.
                            CNC machines only go through the motions

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                            • #15
                              You can just put on a 240 volt single phase input vfd; no derating and full output.

                              PC1-75 - about $1000.

                              http://www.polyspede.com/pc1_series.html

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