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  1. #1
    Join Date
    May 2018
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    Cairns, Qld.
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    Default Single phase to three phase motor replacement - Motor Size?

    Gentlemen:- Regarding replacement of an existing single-phase electric motor with a VFD & three-phase unit, I recall reading on this forum that it may be a good idea to go up one size on the new motor; can any of the resident electrical gurus comment on the why & wherefore of this, please?

    I'm considering changing the standard 2hp/1.5Kw drive motor on my AL-300 lathe in this way; thus possibly going up to a 2.2Kw rating on the 3 ph. replacement.

    Regards,
    Halifax

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Perth
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    Default

    In this thread you will see a PDF "VFDs for Newbies" - read this for a detailed explanation - saves me reinventing the wheel.

    https://www.woodworkforums.com/f271/vfds-newbies-232742

  3. #3
    Join Date
    Sep 2010
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    Lebrina
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    Default

    I might well be wrong, but part of the answer will possibly relate to the reasons why you want to replace the single phase with 3 phase and a VFD. I'm guessing that if speed control is the reason or at least part of the reason for the change, then a larger motor could only be a good thing provided it fitted the given hole.

  4. #4
    Join Date
    Jul 2006
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    Athelstone, SA 5076
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    4,255

    Default

    going up in hp/kw capacity may also result in motor frame size difference...meaning a new mount and pulley maybe required.

    if you do go 3ph make sure the the VFD is suitable..ie is the motor going to be 3ph star or 3ph 240v delta. The VFD will need to match.

  5. #5
    Join Date
    Nov 2016
    Location
    Gulfview Heights, Adelaide
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    83

    Default

    Brand new motors can generally can be wired either star or delta, however you will need to check this before purchase.

    Looking at my 4 pole motor chart, it is very likely you will go up a frame and shaft size. If so, you will need a larger pulley bore.

    regards,
    paul

  6. #6
    Join Date
    Jul 2011
    Location
    Adelaide
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    837

    Default

    Quote Originally Posted by paul33 View Post
    Brand new motors can generally can be wired either star or delta, however you will need to check this before purchase.

    Looking at my 4 pole motor chart, it is very likely you will go up a frame and shaft size. If so, you will need a larger pulley bore.

    regards,
    paul
    The star/delta thing is true of IEC frame motors but current NEMA frame motors from Crompton Greaves are wired star internally.

  7. #7
    Join Date
    May 2018
    Location
    Cairns, Qld.
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    70

    Default

    Thank you gentlemen for all the replies.
    H614

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