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Need advice on 3 phase converter

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  • Need advice on 3 phase converter

    An Excello 602 Mill followed me home today. This thing is HUGE!

    Motor says...

    General Electric Triclad
    2 HP
    Volts 220/440
    Amps 6.4/3.2
    RPM 1715

    I'm beyond tapped out due to the mill so if I want to use it anytime soon I must find a very low priced phase converter, at least for the time being. I see a lot of options out there. Static, VFD, Rotary, etc. A lot of info to paw through. I have 220v 1-phase to feed it. How about these $130 chinese VFD's that I seem to be tripping over every place I look? The price is good but I don't want something that will cause damage, advise? I don't feel like trying to build one from a 3 phase motor right now.

    I think I read you lose 1/3 power (or was it torque?) when phase converting? VFD's seem to be the cats pajamas from what I am finding in other threads. Is there a reason I don't want to just use the vari-speed head on my mill instead of using a VFD? Then go with a sub $100 static phase converter?

    School me please!

  • #2
    I think many of the static converters are already over $100.

    A rotary converter will cost you just a 3HP 3 phase motor and some parts. Hopefully a used motor, even a clean junkyard motor that doesn't smell burnt might be OK if cheap.

    A VFD.... I would not buy a Huanyang cheapie... it can be money down the drain because some basically blow up in your face early on. Look on Dealer's Electric, and a couple other sites for cheap prices on brand name VFDs... cheap due to being overstock etc.

    A static converter DOES lose you around half the power.... might not be a problem, so long as you do not push the thing to its limits. You would have to push a 1.5HP cut to really have a chance at a problem.

    A rotary converter loses little or nothing, figure at least 85% of full power even with poor balance, more likely 90%.

    A VFD is good 100% power, and adds variable speed, which is a good advantage. For a 2HP unit, prices can still be cheap, although the sweet spot is usually 1HP for the overstock sites. Downside is that VFDs CAN (but do not have to) overstress the insulation on some motors. If the motor on the machine is an older, expensive, hard to get motor, slapping a VFD on might not be so good. You might need to add some sort of inductor on the motor side of the VFD to cut down the spikes.

    The good news is that older motors had more care taken to get the insulation in the right place, so it might balance out.

    A "VFD rated" motor has usually got better cooling, so it can be run at 1/10 speed and not be cooked. Sometimes better wire, also, although that isn't often hugely important. When you get about 5 or 10 turns in on the coil, the spikes are not much of a factor.

    Generally if there will be an issue, it will be related to poor cooling at slow running speeds, or breakdown on end turns, and once in a while bearing pitting from capacitive currents.
    CNC machines only go through the motions


    • #3
      A static converter, really a starter, will be the cheapest but the motor will only make 2/3 of it's rated power. The next choices would be a VFD or an RPC. Quality versions of either will be much better, but more expensive. An RPC is typically more robust and less likely to fail, but a VFD allows for varying the motor speed.

      I would prefer to have a commercial RPC, but that will be more expensive than a quality VFD.


      • #4
        A quality used/surplus drive is probably a better choice than the Chinese units. I've been watching some drives on eBay and here are some that should do the job: Yaskawa Saftronics CIMR J7AU2P07 (2 HP 2 kVA 230V 0-400Hz $138 w/shipping) Fuji FVR K7S FVR022K7S 2AX (230V 0-120Hz 11 amp 4.2kVA $150 + $20 shipping)

        You might be able to connect a motor run capacitor to the third leg just to run the machine and for very light work. Something like 50-100 uF.
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030


        • #5
          What J Tiers said is dead on.
          Keep in mind that to use a VFD , you need to upsize it 50 % , so a 3HP unit is needed unless it specifically says for single phase input.
          The cheapest "3 phase static convertor" is a capacitor wired to the third leg of the motor from either 240 V power lead.
          Put a push button in series with the cap, and hold it down when you start the motor and release it when it gets to speed.
          The normal rating is 100 Microfarads per HP at 220 volts . These are normally called motor caps and are available at Grainger's
          A 180 to 250 cap should work .

          Green Bay, WI


          • #6
            Originally posted by SirLesPatterson View Post
            An Excello 602 Mill followed me home today. This thing is HUGE!

            I'm beyond tapped out due to the mill so if I want to use it anytime soon I must find a very low priced phase converter, at least for the time being
            I have a 601 that I have been running on a static converter for about 16 years. I have only used it in a home shop environment, so it has not been pushed hard, and have never has a power problem. I have also built 4 rotary converters for myself and others. If it was me I would use a rope start rotary untill I decided what I wanted and had the funds to get it.


            • #7
              I've used the same static converter on my 1.5 hp BP clone for more than 20 years without any problems.
              I have never ran into a situation where my machine was lacking power!!!
              Get a static converter and start making chips.

              That said, everything else, 24" American lathe, 16" South Bend and a Bridgeport run off a home made rotary converter which uses a 5 hp 3 ph. motor, started with a 5 hp Phasamatic static converter, as their power source. The reason the clone is still being run with a static converter is that I have never needed to make that change.

              THANX RICH
              People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!


              • #8
                First of all I have never done this, just heard how to do it. Back in the old days my Dad ran his shop with a 3 phase motor. In the area of MPLS that didn't have 3 phase yet.
                He would said to double the HP, so go out and look for a 4 or 5 HP motor. Run the 2 single phase wires in and connect it to 1 & 7 & 1 lead of the 3 phase motor to it. Then 2 & 8 of single phase to another 3 phase wire and wire then 3 & 9 of the 1 phase together with the other 3 phase motor lead. Then hook 4,5,6 Together by themselves Tape them up good. He had 2 switches one on the single phase and another on the 3 phase going out. He started it s simple with a lawn mower rope. The 3 phase motor has a 4" pulley on it and he cut a notch to put the knot at the end of the rope into. He would wrap the rope around the pulley flip on the single phase and pull the rope and then flip on the other switch and away they went. Call up some scrap dealers or look on CL and get a used one. Some guys hook up a 110 v motor on it to turn the pulley, I suppose it is a lot safer too. Rich


                • #9
                  Originally posted by Rich Carlstedt View Post
                  Keep in mind that to use a VFD , you need to upsize it 50 % , so a 3HP unit is needed unless it specifically says for single phase input.
                  No, no, no, NO! This is a myth that keeps getting propagated and it is only true in a specific circumstance, that being the VFD was designed for 3 phase input only. Almost all sub 5hp VFDs are now made for single or three phase input and will run motors up to their rated capacity with no derating. And even then a lot of VFDs are rated to run down to less than 200v @ 50hz for Japanese mains operation so the chances of you getting an under voltage condition under full load are very slim. I run a lot of "3 phase only" drives and have never had an undervolt error.

                  Patterson, do yourself a favor and just buy a good Hitachi, Toshiba, Cerus (LG), or one of the many other name brand drives and you will be happy.

                  Edit, argh. Didn't read that right. Doh.

                  But the part after my stupidity still stands.
                  Last edited by macona; 04-06-2014, 11:35 PM.


                  • #10
                    I think the main reason why VFDs are rated at lower power on single phase is the size of the DC bus link capacitors and ripple. For single phase, especially at lower line voltages (208V), there must be enough capacitance to hold the voltage above the cutout point (usually 200V). The peak rectified DC voltage from a 220 VAC supply is about 310 VDC, and 2HP is about 1500W or 4.8 amps. There is about 5 mSec between peaks where the voltage drops below 200V, so what is needed is 1500W * 5mSec = 7.5 Watt-Seconds (Joules). The necessary capacitance is about

                    C = 2*7.5/250^2 = 240 uF

                    A 3HP VFD that I recently tried to repair/salvage had 2300 uF of 400V capacitors, so that is more than enough to work on single phase (which was how it was being used, and rated).

                    In that case, the power limit may depend more on the power factor of the VFD and the line current on the 220 VAC supply. For 2HP, the current for a perfect 1.0 PF would be 6.8A, but it could easily be two or three times that at full load.
                    Last edited by PStechPaul; 04-07-2014, 01:45 AM. Reason: PF limitation
                    Paul , P S Technology, Inc. and MrTibbs
                    USA Maryland 21030


                    • #11
                      With most drives you are good for about a 10% range outside their specced range, in the case of most Japanese drives, the rated range is usually 200 to 240v. +/-10% on that gives you down to 180v input so you would have to get the bus voltage down to that point. Even with not-so-great buss filtering you will probably not drop below that level on most drives. Possibly some real old ones.


                      • #12
                        The derate is a serious consideration.... Still....

                        The causes are two-fold. First, the diode rating... That is fairly easy to fix, for the manufacturer of the power module, but many modules still use smaller diodes. Second, the ripple current rating of the capacitors must be suitable for single phase.

                        Drives are going two different directions these days.

                        1) low power drives may be rated for single phase, with larger filter capacitors, both to hold up voltage, AND to carry the high ripple currents (charge and discharge current) inherent to single phase input. BUT they may not be also....

                        2) Drives of all sizes are being designed with minimal filtering, often just a medium sized film capacitor of perhaps 50 uF. The film caps are now much cheaper than they used to be, and also are smaller. 50uF at 400V is about the size of 2 or 3 pocket-sized matchboxes. That size capacitor may be rated for 40+ amps of ripple current. The design is possible because 3 phase voltage never drops below 86% of peak (single phase voltage drops to zero twice per cycle).

                        Obviously, if you have a smaller drive with a proper single phase rating, you are OK.

                        However, the film capacitor will not hold up voltage, even if it can take the ripple current. You won't get a good output from the drive, and it will probably fault on low bus voltage.

                        For a drive with regular capacitors but no single phase rating, the life may be short if you draw rated power, because the capacitors will fail from overheating. They will probably open the pressure vents and leak corrosive electrolyte onto the innards of the drive.

                        Read the specs before purchase.
                        CNC machines only go through the motions


                        • #13
                          The advice to use a static assumes you have a junk box or access to a junk box with a bunch of start/run caps for motors of various sizes, a suitable metal box to put them in and switches.
                          Many HSM used to have these or were associated with industrial facilities that had such or had HVAC friends with such. This is still true for many of us, but less than 20+ years ago. If you buy
                          caps, where they used to be $3-5 now they are $10-20, even at Surplus Center. That assumes you know what cap size/voltage you want. A decent static converter has built in relays for
                          automatic start and shifting from start to run caps. A rotary converter is a static convertor connected to a 3ph motor at least twice the size of your mill motor and uses the 3ph motor as a
                          generator to create a 3ph electrical supply that is then used to run your mill. Again a "surplus" 3ph motor that is a freebie or nominal cost is assumed. If you have to buy and build some
                          part of this then, you are way ahead just going with a name brand VFD. A 2hp 220v 1ph input rated quality VFD is in the $180-250 range, depending on source, new.

                          If you buy a static convertor it will be at least $100, rotary convertors commercially supplied are $300 and up. Maybe you can rummage around and come up with the parts for free, if so
                          then a rotary will certainly do the job. But the speed control ease of a vector VFD is certainly attractive.
                          Last edited by sch; 04-07-2014, 09:59 AM.


                          • #14
                            Thanks for all the info. Pondering.


                            • #15
                              Originally posted by sch View Post
                              But the speed control ease of a vector VFD is certainly attractive.
                              And dynamic braking too.