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Odd questions that cross my mind. Can you run a VFD off a generator?

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  • Odd questions that cross my mind. Can you run a VFD off a generator?

    I have no intentions on doing so (yet), but can a guy run a VFD off a 220v single phase generator? Like I said, I have no intentions of doing it but it is just something that crossed my mind and would be nice to know. In case there is a storm, the power is out, and a guy just has to mill something right now.
    Andy

  • #2
    You could probably run a VFD of a 220v DC source
    because they rectify AC to DC anyways.

    -D
    DZER

    Comment


    • #3
      I can't see why not, the commonest use of a VFD is from single phase AC domestic mains supply and the input of the VFD only has to have the same input voltage. The generator output would normally match domestic so that your normal electric tools and appliances can work ok.

      Comment


      • #4
        If you think where your domestic supply comes from...
        Mike
        WI/IL border, USA

        Comment


        • #5
          Yes. You can. It’s a good way to handle startup loads since you can use it as a soft start.

          Comment


          • #6
            Originally posted by MichaelP View Post
            If you think where your domestic supply comes from...
            It comes from the government, right ?

            KIDDING kidding KIDDING...! ! !

            -D
            DZER

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            • #7
              Originally posted by Doozer View Post
              You could probably run a VFD of a 220v DC source
              because they rectify AC to DC anyways.

              -D
              Not. They are called VFD because they vary the output frequency & voltage which is AC. He said 220 volt single phase AC generator which he owned as the source.
              Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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              • #8
                Originally posted by wmgeorge View Post

                Not. They are called VFD because they vary the output frequency & voltage which is AC. He said 220 volt single phase AC generator which he owned as the source.

                Doozer is right actually. The VFDs rectify AC to DC, then generate a simulated waveform with pulsed output pulled from the DC bus. Not sure how they would work with DC input though, I'd need to think about that one for a minute. Maybe if you tied the DC in after the rectifier. But you'd need more than 220VDC to equal what you'd get out of the rectifier from 220VAC. How about it Jerry?

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                • #9
                  I ran a 1.5 HP 460 VAC 4 pole 3 phase motor using a 7.5 HP VFD connected to the DC outputs of two automotive inverters and some 12V SLA batteries. I added a connection directly to the DC bus link, but it would work just as well with connecting through the bridge rectifier. The voltage from the (240 VAC) inverters was about 150 VDC each. I bypassed the "modified sine wave" section.

                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

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                  • #10
                    I have a constant pressure well pump that is a 240vac in and three phase out to the pump motor. I have run it off of a generator. So to answer your question, Yes you can. And also as said above it is a soft start so the generator does not have to supply a big inrush current to start the motor.

                    lg
                    no nea sig line
                    near Salem OR

                    Comment


                    • #11
                      The question was...Can he run off his 220 volt Single phase AC generator... the correct answer is Yes. How and the heck did DC get into the equation?
                      Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

                      Comment


                      • #12
                        First, yes you probably can run a VFD on generator power. Small generators usually produce a sine wave, just like the generators at the power plants and that should work just fine with almost every VFD. Of course, there could be the odd one that has a problem, but it would probably be hard to find that problematic one. I would totally expect it to work as long as the Voltage and available current are suitable for the VFD.

                        But run a VFD from DC? It may sound OK as the power path in a VFD does first use a conversion from AC to DC. So far, so good.

                        BUT, and I did capitalize that word for emphasis, there is also control circuitry in almost every VFD and that control circuitry almost certainly runs on a LOW Voltage DC which is also generated by converting the incoming AC into DC. The key word here is "LOW". The higher Voltage DC which will be used to generate the output AC waveforms is way too high to power things like ICs which are used in these control circuits. So a transformer or a separate winding on a common transformer is used to produce that low Voltage AC which is then rectified to generate the low Voltage DC (around 5 to 12 Volts) which then powers the control circuitry.

                        So just placing DC on the input power cord of a VFD or even connecting it to the appropriate place inside the VFD will not allow for that conversion of the expected AC input current into the low Voltage DC that is needed to actually operate the VFD.

                        In short and at best, with a DC power input, the VFD will probably just sit there and do nothing. In a worst case scenario, using DC to power a VFD could allow excessive current to flow in any transformers in the circuit and overheat those transformers, burning them out.

                        It is possible for the VFC to generate that low DC Voltage without a transformer, but I can not say that any particular model does or does not do this. So, I do not recommend trying this.



                        Originally posted by Doozer View Post
                        You could probably run a VFD of a 220v DC source
                        because they rectify AC to DC anyways.

                        -D
                        Paul A.
                        SE Texas

                        And if you look REAL close at an analog signal,
                        You will find that it has discrete steps.

                        Comment


                        • #13
                          Originally posted by wmgeorge View Post
                          The question was...Can he run off his 220 volt Single phase AC generator... the correct answer is Yes. How and the heck did DC get into the equation?
                          Nowhere in the OP is AC mentioned. It is presumed from the term single phase since a generator is a rotating DC source and an alternator is a rotating AC source.

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                          • #14
                            The term 220 volt single phase should give you a clue that its an AC generator, yes it should be called Alternator. Yes there are also DC generators that use an Inverter to make the AC.
                            Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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                            • #15
                              It is probably a rarity to find a fairly modern VFD that uses transformers on the line side to produce low voltage DC for logic circuitry, fans, etc.
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

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