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Converting Single Phase to 3-phase

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  • Converting Single Phase to 3-phase

    Due to problems with the contact points arcing & sticking on the centrifugal starting circuit switch of the 3hp single phase motor of my lathe, I'm considering converting it and my mill to 3-phase. If only I'd done more research before buying single phase equipment! The lathe still has a year of warrenty left, and the mill is less than a month old, so it's got almost two full years of warrenty coverage. As foolish as it was to buy single phase machines, I feel it'd be even more foolish to screw around switching them over while they're still covered. The lathe is a chicom machine, but the mill was made in Taiwan - maybe its motor will stand up to on/off operation better than the chicom motor has?

    One motor repair shop I talked to recommended a solid state start circuit control unit (made by Sterns?) that has no contact points as a solution - only drawback is that this control retails for around $100. If it works, it still sounds like a cost-effective solution (as opposed to buying two 3-phase motors for the machines, another one for a rotary phase converter, and ???$$$ to re-wire both machines for 3-phase).

    Could anyone give an estimate of how much work it would be to re-wire the lathe & mill for 3-phase, or is it even practical to attempt to do so?

  • #2
    I don't know how much it would cost to rewire to three phase. But Granger has the solid state relays. I purchased three off ebay. The relays I purchased were similar to ebay item number 6026494618 except that I got three for twelve dollars picked up locally.
    Granger has them but a little more expensive.
    This has worked for me on a pump and a couple of rotary converters.
    Herm Williams


    • #3

      It is more than that. As you probably know it involves changing the motors out for 3phase ones, then adding a static or rotary converter to allow running the 3phase motors.

      While the motors might be able to be re-wound, it isn't worth it to do so.

      Cost? Well, 2 motors and at least one converter, plus labor to do it, if you don't do it yourself. Easily $1000+ with new stuff and contract labor. Less from ebay and DIY.


      Keep eye on ball.
      Hashim Khan


      • #4
        From the hillbilly point of view?

        If you got room, go to auctions, buy larger 3phase machines at thier loss.

        When you get what you want, sell your single phase ones and recoup.

        I saw a nice bridgeport with DRO go for less than $600. I didn't have storage room. BUT at the same auction the power hammer went for a crazy price.
        Excuse me, I farted.


        • #5
          Single phase isn't all THAT bad. If your problem is a crappy Chinese single-phase motor, the simplest thing would seem to be to just replace the motor with a better single-phase motor - new or salvaged.

          It might be possible to just replace the centrifugal switch with a better unit salvaged from an old American motor, but making it fit might not be a trivial task (don't know - never tried. But it's not too high-tech - it's just a switch).


          • #6
            If it's under warranty surely the company must put the problem right by law.If they cannot do this ask for your money back that's what we do here.
            David Coffer said
            I saw a nice bridgeport with DRO go for less than $600. I didn't have storage room. BUT at the same auction the power hammer went for a crazy price.
            David I too see good stuff go at auctions second hand stores all the time I always wonder why people are so shy of buying used stuff it aint all bad.Alistair

            Please excuse my typing as I have a form of parkinsons disease


            • #7

              Just look at me, I'm about all used up. But the wife thinks she has gotten a bargain.
              Excuse me, I farted.


              • #8
                Grainger and most motor shops have replacement centifugal switches and flywieghts.

                You might alos see if the motor start capacitors have a bleed down resistor on them,If not a 15-25k ohm 1/4watt resistor across the capacitors contacts will sometimes help.
                I just need one more tool,just one!