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Thread: Single phase transformer for a welder

  1. #1
    Join Date
    Feb 2016
    Location
    mi
    Posts
    62

    Single phase transformer for a welder

    I have to hook a 37500 transformer up for a single phase spot welder tomorrow. It was already hooked up and ran for years but they moved the welder and want the transformer in the air now. I know #4 were run on the high side before, but not what fuses. Mainly just looking for any heads up you can give me, I think it should be pretty straight forward but never done it before.

    Thanks
    Mielectrician

  2. #2
    Join Date
    Feb 2004
    Location
    Shelby Twp. MI, near Detroit
    Posts
    342
    Voltages???

  3. #3
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,083
    170320-1406 EDT

    What is a 37500 transformer? What kind of spotwelder? Capacitor discharge, or low voltage transformer?

    I assume low voltage transformer which means the welding electrodes connect to a transformer with a single turn secondary. What KVA size does that transformer look like?

    What are the input voltage and current ratings to the welding controller?

    What are the primary voltage and VA rating of the 37500 transformer?

    .

  4. #4
    Join Date
    Jul 2005
    Location
    Tennessee
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    15,269
    I may be uninformed but I know of no special considerations for circuits supplying transformers for welders. Assuming 480v primary a #4 would likely be suitable for the primary of a 37.5 kva transformer protected at 1.25%. For a #4 the max OCP would be 90 amp,
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  5. #5
    Join Date
    Jul 2015
    Location
    Colville, WA
    Posts
    347
    Quote Originally Posted by gar View Post
    170320-1406 EDT

    What is a 37500 transformer? What kind of spotwelder? Capacitor discharge, or low voltage transformer?

    I assume low voltage transformer which means the welding electrodes connect to a transformer with a single turn secondary. What KVA size does that transformer look like?

    What are the input voltage and current ratings to the welding controller?

    What are the primary voltage and VA rating of the 37500 transformer?

    .
    37.5 kVA

  6. #6
    Join Date
    Feb 2016
    Location
    mi
    Posts
    62
    It's a 37.5kva. I don't know much about the welder but we're using#4 high side and #1 low side. They must've had it on 80A fuses so that's what we're going with. Thanks for the help and sorry for the rambling question.

    Thanks
    Mi electrician

  7. #7
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,083
    170320-2152 EDT

    MiElectrician:

    Peak inrush current to a transformer is random in magnitude from one application of power to the transformer to another. Do you know how large this can be, even when the transformer secondary is unloaded, and its typical duration? Do you know what the trip-time characteristic of your fuse is?

    You never answered the question of what voltage you were working at. From some of your new information it now appears that the input is 480 and the secondary is 240. The 480 part is fairly clear because you suggested a fuse size. The secondary is more a guess, but indirectly by some of your other information it can be guessed at. Tell me how I might guess at 240 from your information.

    To get useful help you need to provide the nesessary information in your question in sufficient detail that those that may answer don't have to guess about details that you know about.

    .
    Last edited by gar; 03-20-17 at 10:19 PM.

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