Announcement

Collapse
No announcement yet.

VFD question..single phase input into a VFD ment for 3phase....

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

  • VFD question..single phase input into a VFD ment for 3phase....

    I have been poking around with google searches and such, and I have come accross this tidbit 2x...

    If you have a VFD that is designed for 3 phase input, you can use it to power a 3phase motor from 1 phase input, but de-rate the VFD by 50%.......

    Is this true?... any negative impacts?

  • #2
    Not with mine. My vfd is rated at 2HP and I'm running a 1HP motor. Single phase in, 3-phase out.

    Many of the Allen-Bradley VFD manuals are available on line as PDF files if you'd like to explore further. They do a great job of describing the features and deratings.

    Comment


    • #3
      It entirely depends on the drive. No fixed rules, although the 50% is "reasonable".

      The main limits are the diode rectifiers, which get hit harder with current peaks on single phase, and the filter capacitors, which must carry a lot more current with single phase. The latter is because the filtering requirement on 3 phase is light, 3 phase rectifies to a decent raw DC with NO filtering, so the capacitors tend to be small, and the voltage variation with single phase is larger.

      The manufacturer will probably either give a rating, or disallow use on single phase altogether. Sometimes you have to connect L2 and L3 together to fool the phase loss protection.

      Even if the manufacturer does not rate the unit, you may still be able to run single phase input, but you might be on your own.

      If the drive has + and - DC input terminals, as some do, you can supply your own rectifier and filters, and run at full rated power, assuming you can get it from the mains.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

      Comment


      • #4
        Many VFD's up to 3 hp allow use with single phase input power with no de-rating, over 3 hp most recommend a de-rating factor of 50% as mentioned above. In any event they do make dandy phase converters for single motors!

        Dave

        Comment


        • #5
          Low speed via VFD

          Originally posted by dp
          Not with mine. My vfd is rated at 2HP and I'm running a 1HP motor. Single phase in, 3-phase out.

          Many of the Allen-Bradley VFD manuals are available on line as PDF files if you'd like to explore further. They do a great job of describing the features and deratings.
          Thanks Dennis.

          That post was right on the money as the timing could not have been better so far as I am concerned.

          I think that out lathes are identical.

          I have just ordered a 2HP VFD and I was wondering what the specs are for the 3-phase motor you used are.

          Was it a straight changer-over or did you have to modify the lathe or motor?

          Can you post some pics and the specifications, details, type of mounting (plate?) and any mods needed please.

          So far as I can see, there are quite a few here in Canada that have the same lathe from Busy-Bee that might be interested.

          My need is not due to the gear-box etc. as other than low speed, it is quite OK so far as I am concerned.

          The low 116RPM is higher than I like for screw-cutting, form-tooling and machine reaming etc.

          What is the lowest practical speed on your lathe now that you have the VFD fitted to it please?

          Comment


          • #6
            I'm running a 1/2 hp motor using my 2 hp VFD off of 220v 1p. The front cover of the manual says if I ran mine off 120v 1p it would supply 1 hp 3p.

            Comment


            • #7
              it may be worthwhile mentioning a few power and speed facts about VFDs. Power is proportional to the product of torque and speed. Power is what cuts metal.

              In a range of middle speeds around and below nominal motor speed, the full motor HP is available,.

              At nominal speed, the torque and speed combine to produce full HP per the motor nameplate, it is essentially the same as plugging into the wall (very slight voltage reduction).

              Over a range below nominal speed, while the speed is lower, and power would normally be lower, the V/F characteristic allows a higher voltage (and higher current, meaning higher torque) to be supplied (depending on drive type), so that normal, or near-normal power may be still supplied.

              at lower speeds, the torque is limited because the current is limited, so power drops with speed. This is why the VFD (constant torque) is not a good substitute for a gearbox/back gear (constant power).

              At higher than nominal speeds, the power SHOULD go up, but available voltage may not be able to drive the current through the windings at the higher frequency, so again there is a limit. This tends to be a more constant HP area.

              if the voltage were available to produce it, a 1 HP motor would develop 2 HP at double normal speed (and same motor current).
              CNC machines only go through the motions.

              Ideas expressed may be mine, or from anyone else in the universe.
              Not responsible for clerical errors. Or those made by lay people either.
              Number formats and units may be chosen at random depending on what day it is.
              I reserve the right to use a number system with any integer base without prior notice.
              Generalizations are understood to be "often" true, but not true in every case.

              Comment


              • #8
                You know there are also a WIDE range of VFD's designed for single phase input (up to 3hp at least) for the hobbiest/light industral market?
                http://www.tools4cheap.net/products.php?cat=46 is an example of abunch..
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                Comment


                • #9
                  Some Telemechanique vfd's are dual rated up to 7.5hp (10hp name plate on 3ph). It's not as odd as some might expect. It's certainly not limited to 3hp.

                  Comment


                  • #10
                    Dealers Electric always shows up at the NAMES and Cabin Fever Shows
                    They have a huge number of VFD's
                    Rich

                    http://www.dealerselectric.com/?gcli...FQshDQodclyMEw
                    Green Bay, WI

                    Comment


                    • #11
                      As usual the answer is "it depends". If you are running a pump or compressor to the motor's full ratings, then you will have to derate a three phase in VFD by half to ensure the life of the input diodes and filter caps.

                      If the motor is running a machine tool, then you have to take the duty cycle into account. A 5 HP motor only draws 5 HP worth of juice when it fully loaded like pumping water 24/7. If the motor is partly loaded the VFD running the motor supplies only the demand to maintain the mecchanical oower to drive the mechanical load. The typical home shopper seldom runs his machine to capacity therefore he can use a 5 HP three phase in VFD to run a 5 HP motor.

                      A machine tool in a commercial shop may be run to raatings several times a day and if rapid stock removal is essential the VFD should be sized to suit the load.

                      Here's where it gets a little hairy. When you turn down a VFD's freqency you also turn down the duty cycle seen by the inpur diodes etc. It's like a transformer. If you run the motor at full load nameplate Amps at 30 Hz the VFD input diodes see roughly 1/2 the full load current. The VFD acts like a transformer in this respect. This makes sense: a 5 HP 60 Hz motor running at full load at 30 HZ develops 2 1/2 HP but at full motor torque. It's high school physics.

                      If you were to compare your motor's nameplate with the VFD's you would find the Amps may not agree. Most VFD's are rated generously for the motor HP they are intended for. If you consider the motor's full load amps Vs the VFD's and do the math you would find the VFD could be made to deliver the motor's full load Amps somewhere between 33 Hz and 46 Hz and still be within ratings for for the input diodes and the ripple current for the filter caps.

                      All this is intended to illustrate the fact that when it comes to de-rating a three phase VFD to run from sngle phase power, a simple de-rating factor cannot be rationally applied. You have to compare nameplate ratings, service conditions, duty cycle, crunch some number, and maybe look into a crytal ball.

                      Clear as mud? I thought so. My experience is I ran a 5 HP lathe motor on 5 HP three phase input VFD for 6 years and I ran the snot out of it. There were many heavy full HP cuts at max motor Amps. Considering the time between cuts for cranking back the carriage, chip handling, size checks, and part changes I would estimate the max duty cycle was about 60% and that is why the VFD held up. The input diodes were never overloaded for more than a minute or two. That VFD is still running my turret mill.
                      Last edited by Forrest Addy; 03-31-2010, 01:50 AM.

                      Comment


                      • #12
                        Unless you are awaer of teh parts used, you CANNOT make the determination with any reliability........

                        A full HP load can overload the input diodes, but they may take it because the input power factor IMPROVES at heavy load... the "conduction angle" is longer, and current more closely follows the sine wave, which means the diodes run closer to rating.

                        If the filter capacitor is undersize for single phase, that makes it better on the diodes, as they see even longer conduction angle.

                        BUT, that sort of operation is REALLY TOUGH on the capacitor, which may be the real limit on single phase. That stress tends to be cumulative, and depend on heating.... so it is usually not a case of quick failure. But eventual failure is assured, generally with a "boom" and breakers popping.

                        Depending on how the capacitor(s) was selected and rated, the failure may take a very long time, or it may occur in weeks.
                        CNC machines only go through the motions.

                        Ideas expressed may be mine, or from anyone else in the universe.
                        Not responsible for clerical errors. Or those made by lay people either.
                        Number formats and units may be chosen at random depending on what day it is.
                        I reserve the right to use a number system with any integer base without prior notice.
                        Generalizations are understood to be "often" true, but not true in every case.

                        Comment


                        • #13
                          This is how I see it.If you buy a VFD that is rated for single phase input and is stated to yield X amount of HP then the mfg has tested it and the unit is warrantied to fulfill they're claims.

                          Some mfgs will kindly give you the basic information as to what can be expected if a 3~ input unit is ran on single phase,they may or may not cover that in the warranty.

                          Now,all that aside,if you were to come across some used units,or surplus new ones at a cheap price,then the 50% rule may serve as a starting point.At least the VFD has some ability to protect itself so one screwup doesn't mean instant flames.

                          IMHO if the machine is something that you intend to run reliably at a decent duty cycle and you intend to buy new,then it's worth the extra few bucks to get one with a proper rating.
                          I just need one more tool,just one!

                          Comment

                          Working...
                          X