Needing slightly more help on Phase converter.
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  1. #1
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    Default Needing slightly more help on Phase converter.

    So I watched a good Youtube video on building phase converters. Which helped me significantly figure this out.

    So I am currently at 120 micro farad between L1 and ghost leg, as well as 120 micro farad between L2 and ghost.

    Numbers are off right now still. Im at 258 L1 and ghost and 253 between L2 and ghost, 248 between L1 and L2 So should I continue to lower the capacitance to bring the legs down?


    It currently runs with those numbers. Which is a huge step for me from where I was a month ago.

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    I just dropped capacitance from each side to 90 micro farads, and I am now 148 between L1 amd L2 and 150 and 151 between both and the ghost leg.

    The motor is a 20hp 3450rpm does this sound right to anyone? Just seems low.. bu I will try my 15hp planer and see what happens.

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    Well it didnt start the planer. And now for some reason my laser tach meter doesnt want to work, so I cant tell what speed the motor is running at either

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    i assume those voltages are typos in your second post.

    at no load, 258 volts isn't a problem if you're trying to get a 20hp idler to start a 15hp planer.

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    Cool, I bumped it back up to 120 micro farads and it started the planer. Should I run the planer and check voltage? Maybe I will need to bump the capacitance up a little more.

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    Also when starting the planer, it bogged down the idle motor a lot as well. Took a few seconds for them both to jump up to speed

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    Quote Originally Posted by MetalArtistCandy View Post
    I just dropped capacitance from each side to 90 micro farads, and I am now 148 between L1 amd L2 and 150 and 151 between both and the ghost leg.

    The motor is a 20hp 3450rpm does this sound right to anyone? Just seems low.. bu I will try my 15hp planer and see what happens.
    Motor speed is not important, actually that motor will run at 3600RPM with no load. The name plate speed is what the motor speed will be at 20HP load. Nor does the RPC motor speed have to be near your planer motor speed. A 900RPM motor will run a 3600RPM motor. Motor speed no load is a function of line frequency and rated speed is what the RPM will result when under name plate load due to slip. Furthermore I found that slower higher pole motors make better RPCs than the faster ones! In addition unless you fully understand the functions of the capacitors and not how to set them up to get optimum performance your better off simply using one to start the RPC and disconnect it after the RPC is up to speed. I have seen more problems created by improper capacitor connection than issues running without them.

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    The voltages that you quote are referred to as "high leg three phase". your planer will work fine. Chasing precise voltages from the converter is a waste of time. regards, Clark

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    I think the mfd value is 12 - 16 mfd per phase per hp.. I built a 5hp 3600 rpm unit with a static starter once and used for quite awhile in my shop until I got three phase from the power company...I had a 60 mfd across one line and the generated leg and 80 mfd across the other line and generated leg.. I think I used 440 volt start caps...Worked well and the idling amps dropped from 12 on 240 single phase to 4 on the same line....

    I then got a T30 Ingersoll compressor with 5hp 3 phase motor and it would not start if there was much pressure in the tank usually even though the unloader was working properly..The next motor in size was a 3 hp Westinghouse 3 phase on my Kearney and Trecker mill and it started fine but it does have a clutch..

    The high voltage on the generated leg was never a problem with any of my machines.. I think the generated leg was around 255 volts as I recall....
    Cheers; Ramsay 1

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    What are your voltage readings when the planer is running under load?

  11. #11
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    Got all 450 micro farads split between L1 and ghost and L2 and ghost. When I pulled a amp draw before I turn on the planer, I get 20 amp, on L1 and L2, and when I turn the planer on, the amps drop to 14amps on each leg.. that does not seem right. Curious why the amps drop when I turn the planer on.


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