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

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  • #31
    A 480 VAC sine wave will have peak voltage of about 679 volts, so a conventional PWM algorithm would need at least that much, plus a few volts for the voltage drop in the IGBTs, and a bit more to avoid distortion from ripple on the DC bus link (if the supply is AC). But there is a way to "overdrive" the PWM to get a higher than expected AC output. This is known as "overmodulation" and is a result of "space vector control" and "field oriented control".

    https://microchipdeveloper.com/motorvermodulation

    https://microchipdeveloper.com/motor...ulation-viewer

    http://ijssbt.org/volume1.1/pdf/16%2...hree-Phase.pdf

    https://training.ti.com/teaching-old...xis-decoupling

    (Too much information?)

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

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    • #32
      Yes, a VFD will run off any AC source that provides the correct AC peak voltage, and some reasonable waveform similar to a sine. If peak is lower than a sine wave peak, the VFD may not reach full power.

      Most small generators produce a sorta crappy sine wave, some are better than others.

      As for the DC question, yes, VFDs will run just fine off DC. In fact, many "system VFDs" are made with no rectifiers at all in the individual drives, for machines with many motors. One rectifying front end unit supplies many VFDs in the machine. In some cases, the front end is bidirectional, it can rectify, and it can also send out AC to dump excess energy from the DC supply that may occur during braking of a number of motors at once. Usually, motors that are slowing just supply their excess energy to the other motors that are running.

      There is no "magic", DC is DC, and if it is at the right voltage, and stable, the VFDs can run off it just fine. Any VFD can, as long as you have terminals to apply the DC to.

      I do not know of any modern VFD in the class "we" would use, that still uses an iron transformer for control voltage.... that's been old tech for 20 years or more.
      2730

      Keep eye on ball.
      Hashim Khan

      Everything not impossible is compulsory

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      • #33
        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?
        This just says that, most (not all) VFD's can even be run of a bank of batteries with enough voltage/current.
        Helder Ferreira
        Setubal, Portugal

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        • #34
          Originally posted by J Tiers View Post
          Yes, a VFD will run off any AC source that provides the correct AC peak voltage, and some reasonable waveform similar to a sine. If peak is lower than a sine wave peak, the VFD may not reach full power.

          Most small generators produce a sorta crappy sine wave, some are better than others.

          As for the DC question, yes, VFDs will run just fine off DC. In fact, many "system VFDs" are made with no rectifiers at all in the individual drives, for machines with many motors. One rectifying front end unit supplies many VFDs in the machine. In some cases, the front end is bidirectional, it can rectify, and it can also send out AC to dump excess energy from the DC supply that may occur during braking of a number of motors at once. Usually, motors that are slowing just supply their excess energy to the other motors that are running.

          There is no "magic", DC is DC, and if it is at the right voltage, and stable, the VFDs can run off it just fine. Any VFD can, as long as you have terminals to apply the DC to.

          I do not know of any modern VFD in the class "we" would use, that still uses an iron transformer for control voltage.... that's been old tech for 20 years or more.
          So Jerry without tearing the VFD apart do you just connect the DC to the input terminals of a off the shelf unit? Can you post the source and model numbers of those DC input VFD's?
          Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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          • #35
            Originally posted by wmgeorge View Post

            So Jerry without tearing the VFD apart do you just connect the DC to the input terminals of a off the shelf unit? Can you post the source and model numbers of those DC input VFD's?
            Most decent VFD's have terminals that expose the DC bus, connect to that.

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            • #36
              Originally posted by Paul Alciatore View Post
              The term generator applies to both AC and DC generation devices. The term alternator is applied to generators that produce AC. The term dynamo is applied to generators that produce pulsating DC.

              Both alternators and dynamos fall under the more general term, generator.




              Dr Boyd who taught me electrical machines would disagree with you

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              • #37
                Originally posted by Bmyers View Post

                Most decent VFD's have terminals that expose the DC bus, connect to that.
                So there are terminals for direct connection of wires on the DC buss accessible without taking the device apart?
                Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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                • #38
                  If you want to bypass the input diodes to save the voltage drop,
                  the DC buss is always on the electrolytic caps, so just connect
                  to them.

                  -D
                  DZER

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                  • #39
                    Originally posted by Doozer View Post
                    If you want to bypass the input diodes to save the voltage drop,
                    the DC buss is always on the electrolytic caps, so just connect
                    to them.

                    -D
                    So there are terminals for direct connection of wires on the DC buss accessible without taking the device apart?
                    Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

                    Comment


                    • #40
                      Many VFDs DO have terminals available, but they won't be on the cheap VFDs most hobbyists buy.

                      Originally posted by Bmyers View Post

                      Dr Boyd who taught me electrical machines would disagree with you
                      OK you DO realize there is zero difference between a DC and AC generator as far as the generation of power, right? BOTH a "DC generator" and an "AC generator" make ("GENERATE") AC.

                      The difference comes after that part. A "DC generator" often has a "mechanical rectifier" (the commutator and brushes), but if not, has rectifiers. Those are extra added parts which are not involved with the "generating" process.


                      2730

                      Keep eye on ball.
                      Hashim Khan

                      Everything not impossible is compulsory

                      Comment


                      • #41
                        Is taking a device apart an impediment, should it be necessary ?

                        -D
                        DZER

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                        • #42
                          Originally posted by wmgeorge View Post

                          So there are terminals for direct connection of wires on the DC buss accessible without taking the device apart?
                          Of course. They are becoming much more common in industry now too.
                          I worked on some of these Parker common buss units at least 8 years ago now and I see them quite frequently now a days.
                          https://www.parker.com/Literature/El...2020190124.pdf
                          Cheers,
                          Jon

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                          • #43
                            Something no one has so far mentioned.
                            What happens when someone uses a small generator, barely up to the job, with the usual poor governors, couples it up to their vfd, gets her running with no load and then begins to actually work the machine they are powering.?
                            I have absolutely no experience with this, but I do have some experience with a very large lathe driven by an Hydraulic motor, initially powered by a gas engine with a rough governor driving a pump
                            . Everything rolling round nicely, engage feed, tool begins to cut, chuck slows down, after a couple of seconds delay governor opens wide, old lathe takes off like a bat out of hell, sure made screwcutting big threads fun !
                            We later put a 20 hp electric motor to drive the pump, That was much better.
                            Regards David Powell.

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                            • #44
                              Originally posted by Jon Heron View Post

                              Of course. They are becoming much more common in industry now too.
                              I worked on some of these Parker common buss units at least 8 years ago now and I see them quite frequently now a days.
                              https://www.parker.com/Literature/El...2020190124.pdf
                              Cheers,
                              Jon
                              But not the sizes used on equipment The Home Shop folks are likely to see or use. Frankly with all the wind and solar DC generated its seems wasteful to change it all to AC when the commercial / industrial market can use as is.
                              Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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                              • #45
                                Ya got to get it there first.
                                Edison's solution was steam districts.
                                George W's solution was a transformer.
                                Guess which one caught on?

                                -D
                                DZER

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