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Dynasty 200 Rotary Phase Converter question

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  • #16
    New to the forums here and trying to get some advice re: replacing welders I lost in a fire, but, while I'm hanging around I might as well try to be useful:

    Rotary phase converters are, or at least can be, trivially easy to build. The simplest is just a 3 phase motor with your single/split-phase 240 hooked up to 2 of the 3 power connections, wiring for your 3-phase output hooked up to all 3 power connections on the motor, and a lawn-mower pull-start cord wrapped around the shaft.

    Also requiring essentially no work, if you want a push-button starting rotary and don't feel like cobbling together the electronics, you can purchase one of those "static" phase converters, and hook it up to a spare 3 phase motor. The "static" converters are nothing more than the start circuitry from a rotary converter, and when you use one on a piece of equipment, you're essentially turning that piece of equipment into a rotary converter. Instead of hooking it up to equipment, hook it up to a spare, larger-HP motor sitting in the corner, and voila, rotary converter.

    That being said, don't bother hooking up an inverter-powered welder like the dynasty to a phase converter. They don't need 3-phase input, and other than conceptually /maybe/ being able to pull slightly more power from your single-phase supply if you use an RPC to feed their third input, an inverter power supply isn't going to function any differently on single phase 240, than on 3 phase from an RPC.

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    • #17
      Good advice. I have little doubt that I will at least make an attempt to build my own from fabber-cobbled parts I can salvage from who knows where. It's a project off in the near future at the earliest though. Seems simple enough in theory. I also understand the current to not be nearly as smooth as true 3-phase, but apparently there are things to help smooth it out a skosh. But the time I get to it, I'll be more versed.

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      • #18
        http://www.surpluscenter.com/shop.ax...hase+converter
        This may help.

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        • #19
          I have a used phase converter, a 7.5 I paid 400. It is for motor loads. If you want to use second hand machines, a phase converter makes sense. If buying new, buy single phase.

          Three phase power is sometimes 240 phase to phase with two phases to center tap being 120 volts, the third phase to center tap is 208. This is called center tapped delta.

          Another configuration is Wye with neutral. Phase to phase is commonly 208, any phase to neutral is 120.

          In both configurations the middle tap is grounded.

          I prefer Delta 240 because motors are usually built for 230 volts, and will tolerate 10% high or low. The low side being 207 leaves little wiggle room for voltage loss. Motors make more internal heat, and less torque on low voltage.

          Dynasty is equally happy on single phase as it is on three.

          Three phase motors make three phase power. If your phase converter is big enough for your biggest motor, you can use numerous smaller motors on it. It works best to start smaller motors first, then the biggest. Those smaller motors help the phase converter.

          Primitive phase converters were homemade using a combination of small motors. The first needs a means to start it spinning. A rope wound around the shaft like an old fashioned lawn mower works. The first motor will be weak. supplemental motors come on line improving quality of three phase power.

          Willie

          Dynasty 280DX
          Bobcat 250
          MM252
          Spool gun
          Twentieth Century 295
          Twentieth Century 295 AC
          Marquette spot welder
          Smith torches

          Comment


          • #20
            Originally posted by WillieB View Post
            I have a used phase converter, a 7.5 I paid 400. It is for motor loads. If you want to use second hand machines, a phase converter makes sense. If buying new, buy single phase.

            Three phase power is sometimes 240 phase to phase with two phases to center tap being 120 volts, the third phase to center tap is 208. This is called center tapped delta.

            Another configuration is Wye with neutral. Phase to phase is commonly 208, any phase to neutral is 120.

            In both configurations the middle tap is grounded.

            I prefer Delta 240 because motors are usually built for 230 volts, and will tolerate 10% high or low. The low side being 207 leaves little wiggle room for voltage loss. Motors make more internal heat, and less torque on low voltage.

            Dynasty is equally happy on single phase as it is on three.

            Three phase motors make three phase power. If your phase converter is big enough for your biggest motor, you can use numerous smaller motors on it. It works best to start smaller motors first, then the biggest. Those smaller motors help the phase converter.

            Primitive phase converters were homemade using a combination of small motors. The first needs a means to start it spinning. A rope wound around the shaft like an old fashioned lawn mower works. The first motor will be weak. supplemental motors come on line improving quality of three phase power.

            Willie
            I read somewhere a long time ago if a home made rotary converter is not balanced properly, it will send it's dirty power down the line to their neighbors. Is that true?
            Last edited by tackit; 02-08-2017, 07:52 AM.

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            • #21
              Originally posted by tackit View Post

              I read somewhere a long time ago if a home made rotary converter is not balanced properly, it will send it's dirty power down the line to their neighbors. Is that true?
              I guess harmonics could affect neighbor's power. I'd sure be surprised if it was in any sense significant. Your single phase transformer has only a magnetic connection to the primary line. You connect transformer secondary to 1 phase of the first motor, make it spin. Windings in the other phases become a three phase alternator. Again, their connection to the first phase is limited to what the magnetic field induces. I'd say especially if your neighbor is supplied by a different transformer, issues would be negligible. These homemade multi motor devices are notorious power wasters, and don't offer the torque better designs do. I've never seen one operate. An old electrician showed me one he had built. It wasn't connected at the time. I'm repeating information he gave me.

              Willie
              Dynasty 280DX
              Bobcat 250
              MM252
              Spool gun
              Twentieth Century 295
              Twentieth Century 295 AC
              Marquette spot welder
              Smith torches

              Comment


              • #22
                Originally posted by WillieB View Post

                I guess harmonics could affect neighbor's power. I'd sure be surprised if it was in any sense significant. Your single phase transformer has only a magnetic connection to the primary line. You connect transformer secondary to 1 phase of the first motor, make it spin. Windings in the other phases become a three phase alternator. Again, their connection to the first phase is limited to what the magnetic field induces. I'd say especially if your neighbor is supplied by a different transformer, issues would be negligible. These homemade multi motor devices are notorious power wasters, and don't offer the torque better designs do. I've never seen one operate. An old electrician showed me one he had built. It wasn't connected at the time. I'm repeating information he gave me.

                Willie
                Thanks Willie for the info.

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