Announcement

Collapse
No announcement yet.

VFD or phase converter?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • VFD or phase converter?

    I know next to nothing about electricity so could someone please explain VFD vs. phase converter and which would be most suitable for running a 3 phase motor?
    TIA
    Len
    Len

  • #2
    Len, this is funny! I was just thumbing through the KBC catalogue looking at the same thing.
    The old universal mill I just got has a 5hp/208/3ph motor on it and I was wondering if I should use a rotary phase converter or one of those little box looking Phase-A-Matic type converters.
    The Phase-A-Matics cost about !/4 what a rotary unit costs.
    I know I could build one...if I knew absolutely ANYTHING about 'lectricity!
    Well, I've wired a couple houses but that's not quite the same.
    Russ
    I have tools I don't even know I own...

    Comment


    • #3
      VFD
      True 3 phase
      Variable speed
      Motor protections
      can get over normal speed
      can go from 115 in to 230 out, for some models
      full 3 phase motor power out
      full 3phase benefit of "phonographing reduction"


      Phase converter, Rotary
      can be made from a 3 phase motor.
      not quite "real" 3 phase, but close
      full 3 phase motor power out (almost)
      Single speed only
      most of the 3phase benefit of "phonographing reduction"


      Phase converter, "Static", Phase-A-matic box type
      single phase only
      "3 phase" when starting only (actually 2phase)
      about 1/3 to 2/3 motor power available
      "regular" and heavy-duty" available, difference is in start circuit
      Single speed only
      no "phonographing reduction", same as any single phase motor
      Last edited by J Tiers; 05-14-2006, 01:57 AM.
      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #4
        A VFD is not quite "true" three phase. It's more of a pulsed type power rather than a true sinusodial waveform. Absolutely not CNC friendly at all. They do deliver a nice, balanced output which is nice. Downsides are whatever motor is being driven must be started by the VFD, NOT the machine switch. This can be a problem if the machine has multiple motors, like a spindle motor and a power feed motor, or spindle and coolant.

        Rotary's can deliver very balanced three phase but they must be matched to your application to see full potential. Advantages are you can run multiple machines within the current limits, and operate the machines normally by their own controls. So you can use a machines on/off switch, turn on pumps and accessories and such as you would on a real 3phase line.

        As for the little "Phase-A-Matic" boxes; generally not advised. They do not deliver three phase, just a "fake" leg to start the motor, but the motor actually runs on single phase. Serious reduction in power and increase in motor heat. They are OK for very light duty work but you'll never be able to even approch the machines full potential.

        Comment


        • #5
          The "true" part on the VFD is correct phasing, which is only for one power draw on a rotary, and not applicable on static.

          Some VFDs are now starting to appear with a more sinusoidal output even than teh six step type.... theoretically it would be possible to provide a good sinewave output, and some may now do that.

          Phase perfect claims the third phase is done with an inverter on their device, and that it is true sine.
          1601

          Keep eye on ball.
          Hashim Khan

          Comment


          • #6
            If you do a google search on rotary 3ph convertors you will find a couple of good essays on how to build these very simple devices. Static convertors are even simpler, but as J Tiers says produce severe reductions in motor power. Aggregating the necessary pieces for a good rotary convertor is a bit trying for those not familiar. A lot of stuff is available in surplus markets but you have to have some understanding of how this stuff works to select the most appropriate pieces for your application. Depending on your sources, rotary can be dirt cheap or very expensive to make. Cheap or free 5-15hp 3ph motors are the basis of most of these. If you have to buy one then a VFD becomes more attractive. Right now the price leader on VFD for small motors <3hp is www.factorymation.com Their prices on TECO FM50/100 are very good, $50-75 less than I paid 2yrs ago.
            Steve
            Steve

            Comment


            • #7
              Thanks guys! I knew it wouldn't be as easy as buying a cheap box and start making chips but was hoping.
              I USED to be pretty ballsy with electrical stuff but got electrocuted pretty good once while rebuilding an old house. Grabbed a hidden wire that someone had cut off and just left it laying on the top of a heating duct. Now I'm scared sh--less of the stuff
              Oh well, I'm a ways away from even thinking of starting the motor, have to get the rest of the mill home first.
              Be lots of time for studying up on it.
              Russ
              I have tools I don't even know I own...

              Comment


              • #8
                A RPC is like having 3 phase service to your shop,add a breaker box or some other means of distributing it and given a big enough RPC you could power
                all your machines running at once,with out modifacation to controls and auxiliary motors.



                A VFD in general will service one motor.You might have to rework the controls as any contactors will not work with VFD.
                I like the vfd ,as i have set it to slowly accelerate to full power and can see in that few seconds if i have left the clutch in , or if there is going to be a disaster i can shut down.apparently they are very economical on power.

                although i have a RPC for big stuff , I am putting vfds on my small motors as funds permit as i like there advantages.



                search this forum for vfd, also the PM site - I know this came up a few weeks agohere.

                there is a very good article in HSM or MW by Forrest Addy,alsoon PM and I think copied here.

                Comment


                • #9
                  Originally posted by torker
                  I ...got electrocuted pretty good once while rebuilding an old house.
                  If you did, you wouldn't be here telling us about it. You just got shocked. I know the feeling, by the way -- it does tend to make one a bit more cautious!

                  Comment


                  • #10
                    A Phase Perfect from http://www.phasetechnologies.com/ is an easy, but not inexpensive, solution to getting 3 phase power when you only have single phase available.

                    cheers,
                    Michael

                    Comment


                    • #11
                      Almost "phased" off my chair when I read the prices.

                      Whole darn lathe isn't worth that much!
                      Len

                      Comment


                      • #12
                        Originally posted by pstephens
                        If you did, you wouldn't be here telling us about it. You just got shocked. I know the feeling, by the way -- it does tend to make one a bit more cautious!
                        Hahaha...you're right! I only got killed a little bit Wouldn't have been so bad if I hadn't fell off the ladder to boot. Probably helped though, the step ladder peeled out from under me and I fell breaking the contact. Got a nice burn on both hands.
                        Lesson learned! Keep one hand in your pocket!
                        I have tools I don't even know I own...

                        Comment


                        • #13
                          I said it wasn't inexpensive.

                          On the other hand, the PP isn't a permanent installation (move it with you everytime you move), and it doesn't care what you switch on/off downstream from it. You can plug a bunch of small 3 phase loads into it, or one big one, so it is pretty versatile that way. If you've got several devices that need 3 phase and have to buy and configure a good-sized VFD for each one that won't be terribly cheap.

                          It isn't something that fits everyone's budget, but if you are looking for clean and stable 3 phase it seems to be an option that should be considered. People who have a PP seem to uniformly be happy with them.

                          cheers,
                          Michael

                          Comment


                          • #14
                            Originally posted by thistle
                            A RPC is like having 3 phase service to your shop,add a breaker box or some other means of distributing it and given a big enough RPC you could power
                            all your machines running at once,with out modifacation to controls and auxiliary motors.
                            This is what I plan to do - I would suggest putting a switch between the single phase source, and the RPC. No sense running it when you ain't using it. I would also suggest using twist lock connectors between the two panels and the RPC, this way upgrading the converter is very straight forward, just unplug one, and plug in another. This is most helpful when you plan to upgrade to a larger phase converter in the near future.


                            HTRN
                            EGO partum , proinde EGO sum

                            Comment


                            • #15
                              Phase perfect is only one of many, and is over-rated and way too expensive to boot (but works)

                              Ronk, Phase-A-matic and others make RPCs also, around $400 or so at cheapest.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment

                              Working...
                              X