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Thread: Inverter + Phase-Converter = What?

  1. #1
    Join Date
    Dec 2011
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    Inverter + Phase-Converter = What?

    Phase converter topics have been discussed at length in the archives, but I didn't see a clear-cut answer to the question:

    Will an inverter welding power supply perform well w/ 3-phase current supplied by a:

    i) rotary phase converter (RPC), or

    ii) VFD

    If the answer to both these questions is No, then the follow on questions about the wisdom of using a converter, how to set up the system, etc are moot.

    Here're the power choices I've got:

    i) 220v 50A single phase

    ii) 15hp Frequol VFD, rated 46A out (when supplied by 3-phase)

    iii) 10hp RPC (nameplate full load amps on Baldor 3-phase motor, 24 @ 230v)

    And here's what my PowCon 400SMT power supply is claimed to be capable of:

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    Supposing that either converter would be capable of supplying 25A @ 230v 3-phase, It looks like there'd be welding amps to be gained by using one of the phase converters. Is that your take as well, gents?

    BTW, both the RPC and VFD are sitting on a shelf, so cost isn't really an issue.

    Thanks very much.

  2. #2
    Join Date
    Jan 2012
    Leander, TX
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    Re: Inverter + Phase-Converter = What?

    Hmmm, In truth, switching to three phase gives you no more true power from the wall (power in has gotta be equal to power out). In fact, you will actually lose some power in the process.

    I suspect the boost you get from the welder is because the three phase input allows less stress on each input phase of the welder (current is shared by three phases), rather than all the current coming in on one phase.

    It may also be because the three phase input would have less incoming ripple than the single phase, which would allow less supply droop between charging cycles, so you could actually get more current out of the welder with the same input current since the phases were split up.

    I'm not confident you'll get more out of the welder, though, unless you are going to run it at max amps. The output versus input current curves for the two operating modes might be darn similar until you get towards the maximum, where the three phase keeps increasing while the single phase tops out..

    I would think a VFD would run it fine, actually, since most inverter welders have PFC that would keep the VFD very happy (versus a high horsepower, very inductive AC motor). I'd be nervous about using a rotary phase converter (or VFD for that matter) at close to its full load. You want some margin in there.

  3. #3
    Join Date
    Oct 2009
    Palmer, Alaska
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    Re: Inverter + Phase-Converter = What?

    I have seen 110v electronics in 3 phase machines not like "dirty" vfd power and have to be run on a different line from a regular outlet.
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  4. #4
    Join Date
    Feb 2012
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    Re: Inverter + Phase-Converter = What?

    The manual for my budget 5 HP VFD says it is for motors only.

    I would be very comfortable running the welder on a rotary phase converter. The bigger the better. No sensitive chips to leak magic smoke.

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