Rotary phase converter

Discussion in 'General Electronics Chat' started by Brad Buchanan, Mar 9, 2014.

  1. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Hey folks.

    This is an update on my project to build a rotary phase converter.

    I bought a 36" bandsaw at an auction and it needs 550volt 3 phase power. I bought a 5hp 575 volt motor and a transformer to boost my 240volt line power to 570 volts.

    I assembled my main panel with start and run capacitors (red and blue tags), 600 volt contactors and the hookups.

    My first attempt to start the idler failed as I had the start caps wired to T1 and T2 instead of T1 and T3.

    After that was fixed I threw the main switch which powers the transformer, the 110 volt switch that closed the contactor powering T1 and T2 at 570 volts and the monentary switch that brought the start caps online.

    The 5hp idler motor started in less than a second and ran smoothly.

    Unfortunately the run caps were not in the circuit when I tested.

    Voltages on the 3-phase output were:

    T1 to T2 554
    T1 to T3 460
    T2 to T3 466

    Amperage Draws were:

    Line to transformer (240v) 6.6
    High side (570v) 2.3

    I patched in the bandsaw and it started without drama and ran smoothly. I cut some hardwood with it and it worked perfectly however I noted some slight noise from the motor when ripping some 2 by.

    With the saw idling the line in was drawing 23 amps and the high side 9.6 amps.

    Qoustion: Can I balance the voltages better with the start caps?

    Also I was under the impression that the caps did not store energy (at least much) when operating on AC power. This misconception was dispelled when I touched my finger to a terminal accidentally. I touched the terminals with leads from a 100watt spotlight I had handy to drain the caps down and it smoked the bulb instantly and I had a fat, blue spark when I touched the lead to the terminal.

    Sorry for the long post but I am pleased and excited that I can see progress in this project.

    As always comments pro and con are welcomed.

    Brad
     
  2. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    previous should have said "balance the voltages with RUN caps.
     
  3. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Yes you can balance the phase to phase voltages better by changing the run capacitor values.

    I have a number of direct drive converters that with a good motors I can usually get within +- 10% of the line phase voltage or better.
     
  4. AfdhalAtiffTan

    Active Member

    Nov 20, 2010
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    11
    The cat is priceless... :)
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    He's the supervisor. :)
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a friend working with these found that the modern "high efficency" motors dont make good convertors. the older motors are better, they have better magnetic properties.
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Yea I've ran across that a few times as well where no matter what I did a specific motor would just not work properly in a converter application.

    I was never sure whether it was the motors designs or if I just had weak motors with a partially shorted winding or other defect being all of my converters are built with used motors.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    I would have thought that just for 5HP a better, smoother and maybe even cheaper solution would have been a 5HP 220v motor and a VFD, recoup some by the sale of the 575v motor, although you may have had to list that to Canadian sites.;)
    Also the feature of variable speed!
    Max.
     
    Last edited: Mar 10, 2014
  9. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Hey Max.

    The application is a direct drive 600 rpm motor. Kind of an oddball motor and very expensive to retrofit. The other option was to go with a higher rpm motor and fit a jackshaft and pulley to reduce the rpms.

    I got estimates to rewind the motor for 240 volts and they were in the $2000 range.

    Brad
     
  10. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Hey Tom.

    Thanks for your interest.

    Is what you term 'direct drive different from what I built? I have heard of converters that had a separate motor turning the idler motor but I thought that approach was a bit bulky and complicated.

    Brad
     
  11. tcmtech

    Well-Known Member

    Nov 4, 2013
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