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OT, a little. Need some electrical help

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  • OT, a little. Need some electrical help

    As posted in some previous threads I'm setting up a cnc laser/turret press machine. The facility I hope to install it in has three phase 208v power at 400 Amps. I will need 480v at 120 Amps. Is it a wise idea to try to use an Autotransformer, I have read that after a 2:1 ratio the start to become inefficent. Due to the other options costing a lot more in rent I can handle a "little inefficent" but not at the cost of safety. Has anyone out there tried the 208 to 480 conversion? And is the KVA needs of the transformer just the Volts time Amps or is there an advantage to adding a little extra transformer? I am looking forward to hearing from anyones experience in this matter.


  • #2
    Have the power company upgrade your service, then you dont grow through a hassle when you get your next machine.

    The power company wants you to buy power, let them fix you up.


    • #3
      Oldbikerdude37, I wish that were possible. Talked to the utility co. allready. Unless I could find a way to purchase 1500 dollars of power a month they are unwilling to upgrade. I was fortunate to buy a nice machine very inexpensively and want to use it for hobby work. If I don't find away to power it I will be the proud owner of a 37,000 lb white elephant.


      • #4
        We have 208, and do quite a bit at 480, for grid tie inverter testing etc......

        The 120 at 480 equates to about 275 at 208, so you are OK there. You are looking at about 100kVA actual draw, based on your amp figures.

        I don't know if you will find much useful with autoformers, but regular two-winding units are available, new, and sometimes as surplus.

        Do you need a neutral on the 480 side?

        Your size choices boil down to 112.5 kVA or 150kVA. Wothout knowing the machine I don't know if the 112.5 KVA would do it, or if you might need the 150

        You can get 208 to 480Y, or 208Y to 480 delta, depending on what you need. Shielded or not shielded.

        Federal Pacific Transformer is one source, Hammond is another. hammond is big in so-called "dry type" tramsformers, which you want. You want what is called "600 volt class" transformers.

        The Federal Pacific catalog for 600volt class has sizing and other useful info. Their site is confusing, you need to go to "literature" to download teh catalog.

        No this is NOT the folks who made the bad breaker panels.......... in case anyone is confused by the name.

        Keep eye on ball.
        Hashim Khan


        • #5
          J Tiers, Thanks for the reply, I will be the one throwing the disconnect here witht the transformer. I is a comfort knowing that someone out there has previously done this. The building is very old but most of the electrical service I will be involved with is not too bad looking. I think I may have found what I need at HRG Surplus. (A trip too paradise this weekend?).

          Again thank, Can't wait to upload some pictures of the first cuts thios thing makes. But I'm a few weeks from that.



          • #6
            Originally posted by hoof

            Again thank, Can't wait to upload some pictures of the first cuts this thing makes. But I'm a few weeks from that.

            Yeah that wait is a bitc* isn't it? I have two machines "in process" right now... one needs a board from the manufacturer (on it's way, Fed Ex says tomorrow), and the other needs some "attention" from the manufacturer as someone allowed it to forget it's onboard programming due to a dead battery . That too is in progress, the tech should be here Friday.
            This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
            Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
            Plastic Operators Dot Com