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IndustryArena Forum > CNC Electronics > Phase Converters > Need help building a 30hp balanced RPC for a CNC
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  1. #1
    Join Date
    Aug 2012
    Posts
    113

    Need help building a 30hp balanced RPC for a CNC

    I picked up a hardinge conquest 42 with a 10hp (7.5kw) spindle. Looks like it requires about 60 amps for 115% full load. The guy I got it from said he ran it off a 50 amp breaker and it ran fine.

    Probably picking up a 30hp motor tomorrow. Anything specific I should be looking for when I get the motor? The plate on the motor said it requires 78 amps. Will this also be the case if I'm just using it as an idler?

    I guess my first question is how do I calculate a rough estimate for how many and how big capacitors I should get.

    Sent from my SM-N920V using Tapatalk

  2. #2
    Join Date
    Dec 2003
    Posts
    24223

    Re: Need help building a 30hp balanced RPC for a CNC

    Do a search for the old Fitch Williams RPC design, it should have the tuning features included.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
    Join Date
    Aug 2012
    Posts
    113

    Re: Need help building a 30hp balanced RPC for a CNC

    I've been doing some reading. Seems like people are recommending about 15uf per 1 hp on the run side. Does that sound about right?

    Sent from my SM-N920V using Tapatalk

  4. #4
    Join Date
    Aug 2012
    Posts
    113

    Re: Need help building a 30hp balanced RPC for a CNC

    Also should I run a separate 220 line for the first 2 phase to the machine from the panel box and use just the rpc for the generated phase?

    Sent from my SM-N920V using Tapatalk

  5. #5
    Join Date
    Jan 2015
    Posts
    138

    Re: Need help building a 30hp balanced RPC for a CNC

    The Fitch converter:
    404 Not Found

    The past two times I edited this post, the URL was magically changed to cnczone. Here it is in words:
    www dot cnczone dot com slash FitchWConverter dot pdf

    No idea why it gets changed.
    -----------------------
    Third attempt. Something is autoediting my post and changing the word "practical machinist" (with NO space) into "cnczone". I have attached the pdf.

  6. #6
    Join Date
    Aug 2012
    Posts
    113

    Re: Need help building a 30hp balanced RPC for a CNC

    I found it and read it thanks.

    Sent from my SM-N920V using Tapatalk

  7. #7
    Join Date
    Aug 2012
    Posts
    113

    Re: Need help building a 30hp balanced RPC for a CNC

    Is trying to run a 30hp with say a pony start a stretch for 100 amp service? The load Motor is 10hp and takes 22 amps. I also have 2 servos which are 7.6 amps.

    Sent from my SM-N920V using Tapatalk

  8. #8
    Join Date
    Jan 2007
    Posts
    229

    Re: Need help building a 30hp balanced RPC for a CNC

    Quote " 15uf per 1 hp on the run side..."

    15 didn't work for ME, but 17 did.

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