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Can i install a vfd on my mill

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  • Can i install a vfd on my mill

    I have a grizzley milling machine with a single phase motor. Can I install a vfd on this machine? Has anyone out there done it? Does any one out there have a good source for parts? Thank you.

  • #2
    If you have a single phase motor the VFD will not work.


    • #3
      Originally posted by squirrel
      If you have a single phase motor the VFD will not work.
      Almost surely true........ BUT a slim chance it could, IF your motor is a "PSC" type.

      Almost certainly it is not, but there are single phase VFDs made to work with PSC motors, which are motors with a single small motor run capacitor. Often found as fan motors or gearmotors. Rarely found on machinery, but it is possible, since they are very smooth, unlike the usual sort of single phase motor which is very "pulsy".

      Keep eye on ball.
      Hashim Khan


      • #4
        AS the others said, almost certainly not. The starting circuit of a typical single-phase machine motor does not like it when the motor slows down. A 3-phase motor doesn't need a starting circuit.
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie


        • #5
          Single phase motor speed controlers do exist.
          However...the only ones I have seen have all been 220 volt.
          I would look for one from one of the european suppliers.
          I found one on ebay a few years ago. They are indeed rare.

          A "google" turned this up ....
          (they surely ain't cheap)
          Last edited by johnnyd; 02-24-2011, 07:33 AM.


          • #6
            i had a conversation with a vfd suplier this week and he said he was able to set up the vfd to drive the singlephase motor on my drillpress. the main question probably is, how much torque you loose when you slow the motor down. at 150 $ i just might give it a try.


            • #7
              Convert the device over to a 3ph motor and not lose anything... 3ph surplus motors are CHEAP.


              • #8
                Johhyd and dian.........

                The Invertek (UK) drives sold by Anacon are to drive only the type of motor I described above, the "PSC". They will also drive a shaded pole motor, but those are normally not candidates for machine tool usage, and I am disregarding them.

                From the Invertek datasheet (download from Anacon website, or from Invertek):

                "Designed to be cost effective and easy to use, the Optidrive E2 Single
                Phase is for use with PSC (Permanent Split Capacitor) or Shaded-
                Pole Single-Phase induction motors."

                I happen to know quite a bit about those drives, since the company I work for is associated closely with the US representative for Invertek, who sells to Anacon and others.

                As a rule, they, or other VFD type motor drives, will NOT work with split-phase motors having start circuits.

                For one thing, the speed range is small before the start switch cuts in as you slow down, making the "VF" part of very limited use. For another, the start current is quite high, requiring a very "over-built" drive to start them.

                A PSC type already has a high start current, the regular so-called "split phase" motor is typically worse.

                Not only that, but in order to get decent start torque, all split phase (capacitor or resistance types) AND PSC etc, rely on a phase shift at 50/60 Hz. VFDs normally like to start at low speed and accelerate, but at low frequency, there is no phase shifted start winding current. So a single phase drive must start at or near 60 hz and then shift to the speed wanted, just in order to get starting torque to start the motor turning. So your load needs to be able to accept that.

                One MIGHT be able to over-size a drive to run a regular split-phase motor, but as mentioned the speed range is smaller, and the start requirements are a potential issue. And you will have to start with a larger VFD.

                Keep eye on ball.
                Hashim Khan


                • #9
                  i addmit i dont know much about this. was relying on the info i got. your statement will make me investigate further. thanks.

                  what exactly do you mean by "the start switch will cut in"?


                  • #10
                    Thanks for the education.
                    I knew that I was in over my head,...but I felt the need to help.

                    At least I learned something.
                    (at my age,...that's significant)


                    • #11
                      "the start switch will cut in"

                      Typical machine tool single phase motors have a centrifugal
                      switch in the end bell that cuts the start coil/capacitor out
                      of the AC line when the motor rpm gets up into the low
                      hundreds rpm. The start coil/cap combo provides the initial
                      phase shift needed to kick the motor into motion. It is not
                      designed to carry line voltage and will over heat if not cut
                      out by the centrifugal switch and removed from the power
                      feed. Typically it is 'on' for tens of milliseconds. If you listen
                      when the motor is cut off you will hear the click of the
                      switch closing as the motor slows to a stop. Cheap chinese
                      motors are well known for failures of these switches, which
                      in well made motors last years to decades.


                      • #12

                        And the switch typically opens once the motor is "up to" a speed where it has good enough characteristics running single phase that it will finish accelerating to full speed.

                        However it is a "dumb" switch, it only understands speed. If you slow down the motor below the point where the switch operates, it may close again, applying a huge start current load to the source (mains direct, or VFD).

                        The speed at which the switch operates is typically somewhere above half speed, and isn't super-precise anyway. There is a tolerance, so the range of possible slowing is limited before there is a danger of the switch closing (cutting in) and loading the source heavily.

                        The load on the source at the start may be very heavy. I had a problem getting an air compressor to start once, with a longer-than-desirable extension cord. The air compressor as I recall, normally drew about 8 amperes. With the extension cord, it would spin, but not come up to speed (yes the unloader was good). The centrifugal start switch would not open, it was still too slow for that.

                        I observed the 8A motor to draw over 75 amperes, as measured with a clamp-on meter, and the current was still increasing when I shut it off. VFDs which will supply a starting load of 75A are not common. Most can produce very short term currents of perhaps 2x normal motor current.
                        Last edited by J Tiers; 02-24-2011, 10:33 PM.

                        Keep eye on ball.
                        Hashim Khan


                        • #13
                          o.k., i got it cocerning the switch. i talked to to technician again, and what he said, as i suspected, is that torque will drop off rapidly, when you slow down the motor. if you slow it down by 50%, you get 50% torque (or even less). but you can overdrive the motor as a 3 phase. so that gives you a operating range of 50% - 200% (or even 300% for a short time) from a regular motor, assuming you dont need all your motors torque. i consider this as usefull and just ordered a 1.1 kw unit for roughly 160$. if it doesnt work out, i just use it on some 3 phase motor.


                          • #14
                            Originally posted by dian
                            o.k., i got it cocerning the switch. i talked to to technician again, and what he said, as i suspected, is that torque will drop off rapidly, when you slow down the motor. if you slow it down by 50%, you get 50% torque (or even less).

                            NO...... that guy has it wrong, that's bad information as far as three-phase. For single phase it may be slightly more accurate, but still not really true in the general sense.

                            Motor TORQUE stays about the same, it is POWER that is reduced.

                            Torque is dependent on motor CURRENT. That doesn't change if a VFD slows a motor. (single phase motors don't have smooth torque, which can result in a slightly different result)

                            POWER is dependent on torque AND speed. When you cut speed, you cut power, even though torque remains the same.

                            This is easily provable by physics..... "power" (watts) is the rate of doing "work". Work, or energy, is proportional to force x distance it acts through. Distance here is in revolutions (circumference).

                            So if the torque, which is the force, is the same, but the speed in revolutions per minute is less, then the same force acts through less distance per second, less total work is done every second , and the rate of doing work is less...... i.e. the power is lower in proportion to speed.

                            Keep eye on ball.
                            Hashim Khan


                            • #15
                              sorry, i didnt make it clear, i was talking about the 1 phase application. for some reason the torque drops off rapidly, apparently the motor only starts to turn at 10 - 15 hz. anyways, in a week or so i will find out how it is.