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Upgrading to VFD: questions inside.

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  • Upgrading to VFD: questions inside.

    I have a 220vAC 1hp 1phase motor on my benchtop mill. I want to go to VFD.

    Breakout board is a PMDX 131 and I know I'll need the PMDX-106 driver. This will control the VFD drive and subsequently, the motor.

    When I size my motor, should I stay with 1hp or is there a difference between 1 and 3 phase as far as power/torque requirements.

    I'm also thinking of going with belt drive since the gears I have are noisy.

    Any insight would be great.

    Also, the motor mounts with the spindle facing down..what do you call this type of mount? Will I need a specific motor type to achieve this orientation? Most I've seen have the mounts on the side, this will not work.

    Once again, thanks for all your help,


  • #2
    VFD's made now can often be run single phase. The motor HP is a factor of speed and torque and 1 HP is 1 HP. If the speed on the motor you now have and the speed of the motor you intend to run at three phase is the same you'll be all set as far as the motor is concerened. What you may want to consider is the size of the drive you choose if you are running it with a single phase power source. The drive should be double the capacity of the motor if this is in fact the case. Inverters make a large dc supply and remanufacture the three phase with this. The main job of these devices is to bring the voltage and the frequency up and down proportionetly to give you the speed contol it has to offer. When the three phase go into the drive it firsts see a three phase rectifier to make the bulk dc supply. The the filter capacitors act as real short term batteries to keep the dc available while the ac dips below it's peak voltage. When you run these single phase this time the capacitors need to source the power is lenghtened and a 1 HP drive is unable to supply the needed power. By multiplying the drive size by two, there is enough to carry it through. (technically 1.73 is the multiplyer) the square root of three. Good luck and I hope this is of use to you.



    • #3
      Lots of good info.

      THanks Hoof,
      Unfortunately I cannot find a single-phase VFD above 1.5hp rating. According to your data, I need a 1.73hp minimum, so I'm back to looking at a single -phase in three-phase out 2hp VFD with a 1 hp motor 3 phase motor. Is this correct?

      Thanks again,


      • #4
        How about this one?

        Or this?

        Or this?
        Last edited by DR; 10-26-2007, 09:45 AM.


        • #5
          I'd suggest a sensorless vector drive for the superior performance at lower RPM, it's really pretty close in torque to a DC drive. I have a Hitachi SJ100 on my Lagun and it's got great performance, I leave the belt on the step sheaves about midpoint and the VFD display programmed to display the spindle RPM so I can simply dial up the spindle as I like.


          • #6
            I'll second "rkepler" on the sensorless vector drive. I've got one on my 10EE, and it has great performance. I did have to add an external bank of braking resistors to stop the spindle in under 2 seconds.


            • #7
              Hi, I do not mean to steal Jimno2506's post, but can some one explain the difference between VFD and Sensorless Vector Drive? I have VFD on my mill and torque at the lower speeds is rather pitiful. I was contemplating adding pulleys to the current situation to keep most of my operations near 100%.

              Thanks, Jay
              "Just build it and be done"


              • #8
                I didn't stay at the Holiday Inn last night but I've got an e-mail buddy who's an Industrial controls engineer. He explained it to me once and lets see if I remember...

                All motors lose rpm under load. It's called slip? In the past if you needed a motor to run at a steady rpm regardless of load you had to install a sensor on the shaft. That info was used to correct (vector?) the rpm.

                These modern VFD's sense the slip from harmonics on the power line or some sh*t, and correct without needing a sensor. Hence the term, "sensorless vectoring".

                And that's about all I think I know about that!



                • #9
                  The motor mount you need will be a face mount,56c will be the most common in the US for 2hp and under,don't know what the metric mount equivilent would be.IIRC the 56c will have a 5/8 x 1-7/8 long shaft.
                  I just need one more tool,just one!


                  • #10
                    I'm not am electronics expert or anything close to being one, but let's see if this makes sense.
                    There are 3 types of VFD's, and I'm listing in order of increasing costs; the regular VFD, Sensorless Vector Drive, and Flux Vector Drive.. The costs difference between the first 2 is not much, but the FVD is about 1-1/2 - 2 times the cost of the SVD, and you generally need a tachometer feedback in addtion.
                    The regular VFD gives you control of the motor down to about 10 Hertz(translate this into RPM based upon 1750 RPM [motor base RPM = 60 Hertz]), the SVD down to about 1 Hertz and the FVD down to about .1 Hertz.
                    In addition you can also control the motor over its base RPM. Torgue becomes an issue at lower RPM's and this is where the advantage of the VFD's are, as far as I'm concerned.
                    VFD's are a way around changing belts, mechanical variable speeds and DC drives, with excellent results.
                    As an example let me cite the case of the Monarch 10EE;
                    As originally shipped from the factory the EE had/has a DC drive that is either motor-generator drive, WIAD drive(DC drive with tubes and electronics), modular(DC drive with tubes and electronics, an updated WIAD), and all solid state DC drive. DC drives are very strong especially in the lower RPM's and I'm referring to torgue at RPM's around 100, or less. As it so happens these DC drives are getting old and problematic and the tubes are costly, as a rule, and if you have to buy parts from Monarch, can be quite costly, if Monarch has the parts.
                    In the case of my 1st EE, the original drive had been corrupted, trashed, whatever you want to call it. There was/is a DC workaround to this situation, but it's not very effective. I installed a SVD, at the suggestion of one of the Monarch posters on PM, and the performance of the lathe comes very close, I seriously doubt if you could tell the difference, to matching the performance of the DC drives in torgue down to about 150 RPM, in direct drive. I can go into backgear for better torgue and speed control for lower RPM's.


                    • #11
                      Oh, but Beckley?? You dont have the oh so perrty purple glow... Guess you could install some neon tubes for effect... JRouche
                      My old yahoo group. Bridgeport Mill Group



                      • #12
                        I've got another EE that I'm currently working, that does have an intact DC drive. I may yet get the pretty purple glow.


                        • #13
                          Originally posted by beckley23
                          I've got another EE that I'm currently working, that does have an intact DC drive. I may yet get the pretty purple glow.
                          Yeah, but you'll have to take the headstock covers off to see it. Kind of ruins the ambiance.

                          I think DC has more torque at low speeds than sensorless vector VFD, but with a back gear it likely doesn't really matter. On my mill I have the SJ100 and use it to power tap at 10 rpm with the tap in a drill chuck with no problems in power tapping crappy A36 up to 3/8. Never tried anything bigger.

                          The nice thing with the VFD is that I don't have to move the belt in the step head. Ever. I just left it in the second to the top position and controll the speed with the remote panel. The front of the VFD is programmed to display the spindle RPM in open belt.