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Thread: Can someone tell me the differance between...on 3phase?

  1. #1
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    Can someone tell me the differance between...on 3phase?

    Can someone tell me the difference between a rotary phase converter and a static phase converter? Is one better than the other?

    I can not get 3phase to my house because "it's against our principle" according to the power company what ever that means.

    I would be running an 8hp 3phase motor and possibly a 5hp motor (not at the same time). Also, would I need one for every piece of equipment (ie 2 3phase tools) or could I wire it into a branch off the electrical box?


    Thanks!

    Brian
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  2. #2
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    a static phase converter does not make a true sign wave but uses transitors to replicate three phase power. A rotory phase converter is actually is a 1 phase motor that drives a 3 phase generator. the 3 phase produced from it is realy a true sinasoidle power. the static is cheaper and usually limited to smaller load while the rotory is used on larger loads. you would run either one off of your 1 phase panel and provide branch circuit protection to each load.
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  3. #3
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    Didn't Jeff build a converter a while back? I think he said it was easy, you just had to get a few simple things right. Or was that something else?

  4. #4
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    There are some new static phase converters out that are supported to be better than rotary phase converters. I will try to find the link if I can.

    (edit)
    Well no luck I thought I had it bookmarked but seem to have lost it.
    Last edited by Jay Caughron; 04-16-2011 at 02:11 AM.
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  5. #5
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    In my shop I have a 20 HP rotary converter which eeds a 3phase panel and then the 3 phase machines are wired to that panel. It works great.

  6. #6
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    I haven't personally built one, but had this conversation before. This is a general sense of what I learned talking with some guys that ran a little machine shop and made their own:

    If you are making your own, there is an art to "balancing the load" I was just told get someone that knows what they're doing to do the initial setup for you off the taps. I think it's balancing the voltage from phase to phase based off the tap locations on the motor.
    A lot of static types are rated on operating loads, not startup. Some requrie you to oversize the static converters by about 1/3 larger than the motor you are running.
    Make sure you have enough power to run the thing. It takes a lot of amps to run 8hp motors from a 220 panel.
    Last edited by Jeb Taylor; 04-16-2011 at 04:37 PM.

  7. #7
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    Quote Originally Posted by Bill Lantry View Post
    Didn't Jeff build a converter a while back? I think he said it was easy, you just had to get a few simple things right. Or was that something else?
    If you mean me, yes I built one a while back from plans a buddy of mine designed. His are Cadillac models. Took me a while to scrounge up the parts (EBay mainly) and lucked up on the motor.

    Brian, basically 3 phase is 3 hot wires going to the motor as opposed to 2 for 110/220. You can run a 3 phase motor on 2 legs once you get it running. Static convertors typically just temporarily generate 3 legs long enough to start the motor and it runs on 2 legs and your getting about 2/3's it HP.

    A rotary fires up 3 phase motor, then it runs that motor on 2 legs and uses the 3rd as a generator. That creates the 3rd electric leg for your machine while your 220 service provides the other 2 legs. So you get full rated HP of the motor.

    Keep in mind there are a lot of cheap made Rotaries out there. That is why I built mine. It wasn't that hard but I find this kind of stuff fairly easy. But it did take me a while to wrap my head around the schematics and to understand how to assemble all the parts.

    PS You would probably need at least a 10 hp motor on your rotary to start that big motor. A lot depends on how well the unit is built and how efficient it is. A cheap one might have to be 15 hp rotary motor. Running more than one at a time usually isn't a problem, it actually make then run better. It's just getting the biggest one started that could be an issue.
    Last edited by Jeff Horton; 04-16-2011 at 03:03 AM.
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  8. #8
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    Quote Originally Posted by Al killian View Post
    In my shop I have a 20 HP rotary converter which eeds a 3phase panel and then the 3 phase machines are wired to that panel. It works great.
    Wow, what feeds that 20 HP motor? Is it a single phase 230V supply? That would be at least 70 amps, maybe 80 at full load. And where do you find a single phase 20 HP motor? That must be about the biggest single phase motor they build.

    Mike
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  9. #9
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    Great explanation Jeff, Thanks for that!
    not that I needed the info, but now I'll know when I read or hear about it...
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  10. #10
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    Quote Originally Posted by Mike Henderson View Post
    Wow, what feeds that 20 HP motor? Is it a single phase 230V supply? That would be at least 70 amps, maybe 80 at full load. And where do you find a single phase 20 HP motor? That must be about the biggest single phase motor they build.

    Mike
    Don't you use a 3 phase motor to build these? But yeah I bet it pulls some serious power.

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