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three phase converters

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  • three phase converters

    my neighbor just got a converter for his three phase lathe to run it on single phase. of course it has variable speed control and shows a number in the display area. this thing is pretty small, in fact it would fit easily in a shoe box with spare space. . . . so i looked it up on the net / ebay and it was under 200 bucks american, but it sez in the posting that it will only give you 2/3 of the power of the three phase motor and its not to be used with a lathe without a clutch.

    question i would ask this group is: how do you handle the 2/3 output and what about the "clutch" issue? are either of these situations a real problem or are the manufactures just doing a CYA thing? ? ? ? ?

  • #2
    You're looking at two different devices.

    The one that only gives 2/3rds power is a Static Phase Converter, and basically just runs the motor on two of it's three phases. The benefit is that they're dirt-cheap, if cost is an issue and the power loss isn't.

    The device with the digital readout, however, is a VFD, a Variable Frequency Drive. This is a much better unit, giving true 3-phase power to the motor, and providing a wide range of additional features, such as infinitely variable speed, soft-start, instant reversing, and so forth.

    The drawback is they cost a bit more, and take a bit more work to wire in (you aren't supposed to have switches between the VFD and the motor, so you have to wire the machine's controls to operate the VFD controls. It's not that difficult.)

    In my opinion, the only reason you might want a static converter is if the entire project absolutely has to be done dirt cheap, and it's for a simple, basic motor like a bench grinder or a coolant pump.

    For virtually anything else, get a VFD- especially if you're trying to run a mill or lathe. The features of a VFD become almost indispensible, particularly if you're refitting a lathe (for example) that didn't already have a built-in reverse, or a spindle brake, or had a limited range of speeds.

    Doc's Machine. (Probably not what you expect.)


    • #3
      If it has variable speed control it should be a Variable Frequency Drive (VFD). It is my understanding that there is none to minimal power loss; so that one third loss doesn't make sense. A static phase converter normally gives you a 1/3 loss, but does not provide variable speed. I would investigate a little more.
      My advise would be to stay away from the static converter and go with either the VFD or a rotary phase converter. The choice on those would depend on your needs and your budget.

      Do yourself a favor and see if your TV carrier has America One News Network (AONN). 208 on Uverse. It is good old fashion news, unlike the networks, with no hype, bias or other BS.


      • #4
        You should be more specific about the model you are looking at.

        There are three ways used to convert single to 3 phase
        • VFD = Variable Frequency Drive - can vary speed
        • Static phase converter
        • Rotary phase converter

        Here are a couple VFD vendors.

        2/3 power and clutch issues may be someone getting confused about the difference between VFDs (which can vary speed) and static phase converters (which are junk).


        • #5
          i built a rotary for my lathe. its a single speed motor with a mechanical variable speed head. it works great. my buddy has an identical sized lathe but with a 2 speed motor,built in coolant pump, and brake. his electrician (a licensed master ) talked him into buying a VFD and could not make it work. this lathe has 6,i think, contactors with 115V coils and a transformer. the VFD mfg said it would not work with all those contactors. i built him a rotary and hes happy. the VFD could have been made to work by bypassing all the lathes original controls and wiring direct to the motor. as soon as we find the appropriate 3-phase motor for his change belt,chinese mill/drill,the VFD will go on it. wny supply sells kits to build a rotary. easy and cheap to do.


          • #6
            A static phase converter work very well and the loss of power (you have approx. 77%) is no problem. The problem comes in if you need to reverse quickly like if you are threading or tapping. You need to bring the machine to a full stop first. That is why a lathe with a brake is best. Same thing on a Bridgeport. If you just put the machine in reverse without coming to a full stop-it will continue to run forward and you could have an accident. A static phase converter creates a third phase for only a few second - enough to get you started in the right direction. Also - if you exceed the available power the machine may go into reverse on its own. I had one for over 10 years and it has served me well.


            • #7
              As far as I am concerned static "converters" suck rocks and are a waste of time and money. Actually, they aren't converters at all.

              Consider this:

              1-4 hp static "converter" - $179 and you lose at least 33% of your motor's HP and place your motor at risk.

              3 hp VFD - $185 and you get 100% power and variable speed too.

              Viewed another way, If you upgrade from a static to a VFD, you will gain 50% more power over a static and also have variable speed. What a deal for $10.00
              Last edited by Richard-TX; 10-12-2010, 02:27 AM.


              • #8
                Nobody has hit on the REAL problem with static converters..... (other than special cases).

                "Static converters" run your motor on single phase, and FEED IT single phase..... So it RUNS AS A SINGLE PHASE MOTOR. (it does not run on "two of the three phases", it runs on "two of the three WIRES". Big difference.

                If you had any idea of getting the chatter and finish improvements available with the smooth flow of power in three phase, you can FORGET THEM..... with the static converter, none of that happens.

                A crummy and not well balanced rotary converter is miles ahead, because input torque never goes to "zero".

                A good one, or a VFD, gives you at least all the benefits of 3 phase, or more.

                If all you want is for the thing to "spin", then you are welcome to spend as much or more for a crappy solution as you would for a good one.

                Keep eye on ball.
                Hashim Khan


                • #9
                  I have two invertors with speed control,one for my mill and the other for two of my bigger wood lathes which I use ( needless to say) one at a time.
                  I have a nice big rotary convertor which I had to buy (with help from mark Jones) who was also a great help to me,as the others both static and invertors wouldn't work my lathe as it has variable speed built in.
                  Anyway I did notice a big difference between my rotary convertor and my static which I have since bought a big three phase motor and converteed with a lot of help from my good pal sir John and also the company which makes the static were very helpful TRANSWAVE .I ended up since it was tripping the board all the time having to buy and fit a new complete consumer board with different trip switches as the ones I had were no good for working with rotary devices like electric motors.These things are important if converting a static from static to rotary.I learned a lot about how these work and I wish you well .Alistair
                  Please excuse my typing as I have a form of parkinsons disease


                  • #10
                    so i did it. . .

                    3 hp VFD - $185 and you get 100% power and variable speed too.

                    ok, i ordered one of these. no stock, but within two weeks. i will try it on my "pullmax" hammer as the magnetic starter crapped the bed. if it works as well as i think it will, another might be in the works for my lathe that already has a 4 speed transmission and hi-lo plus reverse in all 8 speeds. . . .

                    thanks for all the input.