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VFD (Variable Frequency Driver) for 3-phase motors.

Discussion in 'General Electronics Discussion' started by Robo_Pi, Feb 12, 2019.

  1. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    Has anyone built a VFD, or know of any schematics or other information on how to build one?

    I have an old 3-phase, 220volt, 1-1/2 HP, 4.2 AMP motor. I would like to build a VFD to run it.

    I know that I can just run out and buy a VFD, but that's not the point. The whole idea here is to learn how to build a VFD.

    So can anyone point me in the right direction for information on how to do this?

    Thanks.
     
  2. Minder

    Minder

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    Apr 24, 2015
  3. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    Ok, I found the following schematic. It seems fairly straight-forward.

    [​IMG]

    What I'm not clear on is how to hook up the 230 VAC at the input of the bridge. This schematic appears to assume a single-line 230 volt 1 phase. But what I would like to do is use a standard residence 220 VAC. That comes in as two 110 VAC lines that are of opposite phase with respect to a common neutral. Is that right?

    I don't know how to hook that up at the input of the bridge to get the 220 VDC at the output. Would I hook up a 110v line to the switch and the other 110v line to where it says 230 volts on the schematic? And if so then what about the neural line?

    I guess what I'm really asking is how to build a 220 VDC power supply using a standard residence electric service. Once I get a suitable 220 VDC power supply the rest of the schematic is pretty simple. Most of the magic will be in the PWM programmed into the MCU. That part I know how to do.
     
  4. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    Another question:

    I would like to start out building a low-voltage prototype. Where would I find a 12 or 24 volt 3 phase motor to test with? Do they make such a thing? I can't seem to find one. Everything I search for in 3 phase seems to be 220 volts.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Think you will find the circuit shown would be a much simplified version drawn up for the purpose of understanding basically how it works.
    There will be a lot more to it including the uC requirements and programming.
    I would not imagine a standard pwm generator programming would be sufficient to duplicate sine waves or the phase timing.

    Low voltage motors ( brushless) are essentially 3 phase motors and will work with mostly voltages from 2s lipo upwards perhaps to 50 volt.
     
  6. Minder

    Minder

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    Apr 24, 2015
    I assumed you are asking for a induction motor VFD?
    For N.A. 220/240 you ignore the centre taped neutral and use the L1-L2 legs for 240vac.
    The typical induction motor VFD not only creates a 3 phase sine wave but modulates it with PWM for energy content of the 3phase.
    M.
     
  7. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    Do they actually have 3 wires for the three phases?

    I'd definitely like to experiment building a low-voltage VFD before moving up to a full-blow 220 volt version.
     
  8. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    I can do that. I can create nice sine waves with something as simple as a 555 timer IC. And then PWM those using an Arduino. So I don't see where there should be a problem producing perfect sine waves. Using three sine wave generators I can phase those three sine waves relative to each other however I want. So I'm not real worried about that end of the circuit. There are probably even better chips to use for generating precise sine waves. I'm from the old school so a 555 IC is the first thing I grab. :D

    In any case, here's the motor I ultimately would like to drive. Don't be discouraged by the appearance. It actually turns as smooth as a Swiss watch.

    Motor (1).JPG

    Here's the tag on it. It's 1-1/2 HP, 220 volts, 4.2 amps.
    Motor (4).JPG

    I just want to do this as a learning experience.

    It doesn't matter if I burn this motor up, or blow up the VFD. :eek:

    And I know better than to touch any high voltage parts. I have great respect for electricity. I do all my own house wiring by the way, so it's not like I haven't worked with 110 and 220. I work with them all the time.

    I would just like to learn how to build a dependable VFD..

    Just for the record (in case you might be curious), I am hoping to purchase a few machines this summer. A lathe, a milling machine, and a surface grinder. These are all old and rusty (kind of in the same shape as the motor in the photo above). But they will all come with 220v 3-phase motors on them.

    I could swap the motors out for single phase motors. In fact, I was going to do that originally. But the guys on the machine shop forums tell me that the 3-phase motors are much better and smoother running with more control.

    I could also run out and buy a brand new VFD for each machine, but hey, if I can build my own why not? Not only will I save money, but I'll also learn a lot about them, and I'll be able to repair or customize them as needed. I might also be buying more 3-phase machines in the future as well.

    So anyway, that's the story.

    I'm willing to take things slowly. As I've said, I would really like to experiment with some low-voltage 3-phase motors first to perfect the design. Like 12 or 24 volt 3-phase motors. Only after I get that down pat will I move up to trying the 220 volt real thing.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is this what you're after?
     
    Robo_Pi likes this.
  10. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    That might work. It says it's for motors up to 2 HP including 3-phase motors.

    I'll look into it. Thanks.
     
  11. Bluejets

    Bluejets

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    Last time I looked, yes.
     
  12. Robo_Pi

    Robo_Pi

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    Yes, I just looked into it and was able to download the article. It's exactly what I was looking for. This article tells you precisely how to build a 220 volt VFD step-by-step, and it will handle motors up to 2 HP. They even offer kits that have the circuit board, components and enclosure. Strangely the kits cost more than you can by a VFD for. But I don't need the kit. All I need are the plans and schematic. And that's all in the article. I can build my own PC Board.

    So thank you Steve! This is what I wanted. Can't beat an article that takes you though the entire build step-by-step.

    This is perfect! And I would have never found that article on my own. Or at least if I did it would have been after searching through a jungle of junk I don't want. So thank you, thank you, thank you!
     
  13. Minder

    Minder

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    Apr 24, 2015
    You may have quite a hard time finding 3phase induction motors for 12v/24v .
    There are many P.M. field 3ph motors but they require a different controller to a induction motor.
    If experimenting with the old 220v motor, it would be wise to ensure it is totally free of moisture internally, before applying H.F. pulses.
    M.
     
  14. Robo_Pi

    Robo_Pi

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    Oct 5, 2015
    I thought there would be a catch. Thanks for pointing that out.

    Yes, I won't be using the motor in the photo as-is. I'm going to completely disassemble it, give it a really good inspection and cleaning inside and out, paint the case, and then reassemble it. I'm getting into a new hobby of rebuilding old (often antique) metal working machines like lathe's, vertical mills, surface grinders, etc. The one's I'll be buying will all have old 3-phase motors on them in about a similar condition to the one in the photo. So restoring these old motors is just one aspect of this hobby. And I still haven't even made a solid commitment to go this route. I might end up just selling all the 3 phase motors and replacing them with single phase motors.

    So this whole deal is just in the idea stage at this point in time. It will all depend on how easily and dependably I can make my own VFDs and how well they work. I'm a hobbyist, so it's all in fun. If I were in business I'd just either go with converting them all to single phase motors, or equipping them all with factory made VFDs, But as a hobby the idea is to experiment and learn new things.

    There's also the profound joy of accomplishment when a goal like this has been conquered. Or the agony of defeat should I fail.

    This is one reason I'd like to start with low-voltage 3-phase induction motors. Less agony if I fail. :D

    But even failing at something like this still results in a lot of learning. So there's always some good that will come out of it.
     
  15. Minder

    Minder

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    Apr 24, 2015
    There are not many of those old 3ph motors out there that are solely 220v, you may also find that some of that vintage are repulsion-induction motors and have a wound rotor and a commutator for the repulsion start. They look like the one posted but are 1ph however.
    Good luck with the VFD.
    M.
     
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