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Thread: How to Build a Rotary Phase Converter

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    Supporting Member bobneumann's Avatar
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    bobneumann's Tools

    How to Build a Rotary Phase Converter

    Part 1: Theory, initial testing, and proof of concept


    Part 2: Assembly, balancing and final testing



    Plans and schematics:How to Build a Rotary Phase Converter-20hp-schematic.pngHow to Build a Rotary Phase Converter-fitchwcon.gifHow to Build a Rotary Phase Converter-fitcht01.jpgHow to Build a Rotary Phase Converter-fitcht02.jpgHow to Build a Rotary Phase Converter-fitcht03.jpgHow to Build a Rotary Phase Converter-fitcht04.jpgHow to Build a Rotary Phase Converter-fitcht05.jpg
    Last edited by bobneumann; 12-01-2019 at 05:29 AM.

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    Crusty (12-01-2019), EnginePaul (11-30-2019), Frank S (11-29-2019), Hans Pearson (11-30-2019), Jon (11-28-2019)

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    Wow, looks like you have discovered the elusive magnetic monoplole in your description of how a motor works. Better patent that pretty quick

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    Supporting Member bobneumann's Avatar
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    bobneumann's Tools
    Quote Originally Posted by Junker2 View Post
    Wow, looks like you have discovered the elusive magnetic monoplole in your description of how a motor works. Better patent that pretty quick
    I told you physics nerds and engineers to plug your ears. Which one are you?

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    Supporting Member mr herb's Avatar
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    mr herb's Tools
    The bearings in your 20hp motor sound rather tired. Are you going to put it outside your shop? I wouldn't want to have to listen to it all day.

    While safety should be important, 47 years ago I built my first rotary converter, and never had all that complexity.

    A delta wound motor works better than a star wound motor.

    I have seen installations where the initial run up was provided by a rope wound around a pulley--like in an old lawnmower

    I prefer a one half hp motor to do the spin up, then it can be disconnected, or just left running.. It wont draw that much.

    Balancing the phases with no load connected wont do much, as any change in the load that your "floater" motor sees would require different capacitors. Better to balance with your largest tool motor running.

    If your wall power goes off, and you have enough sense to turn off your lathe, I would hope that you have enough sense to turn off your converter motor also. If not maybe you should take up gardening.--Not you Bob, the you is directed to a reader

    Bob, I'm not trying to criticize what you you did, you built a beautiful unit. I just afraid that you will scare off some fellows that want to convert single to three phase, but will get worried that it is too complicated. There are those that have enough sense enough not to stick their fingers on live terminals. There are a lot that don't have that sense, and realize it. This is not for them.

    mr herb
    Last edited by mr herb; 12-02-2019 at 06:16 PM. Reason: more comment

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    Supporting Member bobneumann's Avatar
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    bobneumann's Tools
    I appreciate any honest feedback. Positive or not.

    I don't have much frame of reference for how the bearings ought to sound. it's really not terribly loud in reality I wonder if maybe the microphone picked it up more than it should.

    I'm no real expert on the engineering of it. The write up I was following recommended the balancing to be done under no load and give the generated leg 1.08x the voltage of the other legs. It seems legit enough to me. But I can't really say for sure how it will act under heavy load. I know that with the unit running and powering a 5 horse motor that the generated leg voltage dropped from 153 down to about 148. So it seems like under the unit's full load it's going to be in the vicinity of 140. Which is really all we're shooting for right?
    In any case, I don't have any three phase motors big enough to really test it under its full load. But it's going to be used to power a 15 horse screw compressor. So I guess we'll find out just how efficient it is.

    I sure hope that I haven't scared anybody off. My whole point of the video was to show that anybody with some basic electrical savvy can just step through the process one piece at a time and come out with a working unit.

    But thanks again. And I appreciate your compliment.

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    Supporting Member Frank S's Avatar
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    Frank S's Tools
    Bob you should be able to get some indication of how well it will respond to balance loading if you have a way to use additive resistance loading to any 2 of the output legs. Spin up load L1 & L2 take a reading of voltage for both legs and amperage draw then connect L1 & L3 the false leg to the same load take readings then repeat for L2 & L3 By the time you have completed the balancing you may find that you will even have capacitors across L1 & L2 to balance the incoming line voltages due to imbalanced loading elsewhere through out your supply IE the refrigerator starting up or someone using a Hair dryer.
    I'm waiting for the 3rd educational video the first 2 were very explanatory as long as you said not viewing them from a physics or engineer nerd's eyes
    Never try to tell me it can't be done
    When I have to paint I use http://kbs.justoldtrucks.com/

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    Thanks bobneumann! We've added your Rotary Phase Converter to our Electrical category,
    as well as to your builder page: bobneumann's Homemade Tools. Your receipt:





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