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Thread: Balancing rotary phase converter to run three phase VFD.

  1. #1
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    Balancing rotary phase converter to run three phase VFD.

    I need to hook up a small CNC router table. I was hoping the spindle VFD could be run off single phase but it's a three phase only input. So I decided I'd use a small RPC I picked up to a while back. It's a small ARCO Roto-Phase model M. It's rated to start 3 HP max and a combined load of 9 HP, according to the nameplate. It should work. Everything appears to run as expected. It idles at 3 amps on L1 & L2. My capacitor bank consists of three caps and measures 13 amps. This all matches the manual.

    http://www.arco-electric.com/PDFs/IN...pdf?2021-04-17

    Does anyone have experience running a VFD off a RPC? How balanced do the voltages need to be?

    Unloadeed voltages between legs are:
    T1 & T2 247V
    T1 & T3 260V
    T2 & T3 275V

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    Re: Balancing rotary phase converter to run three phase VFD.

    Cool thread - I'll be watching it to learn stuff
    Dave J.

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    Re: Balancing rotary phase converter to run three phase VFD.

    The Arco use a 3 phase motor to generate rather third leg.
    If look close at one end the cut off the shaft. 40 years ago the would buy a a bell to cover up the cut shaft.

    They also add oil fill capacitors to increase the power but this make voltage unstable on third leg witch you see.

    Unloadeed voltages between legs are:
    T1 & T2 247V
    T1 & T3 260V
    T2 & T3 275V
    If you have a wiring diagram I can help you next step.

    Dave

    Quote Originally Posted by forhire View Post
    I need to hook up a small CNC router table. I was hoping the spindle VFD could be run off single phase but it's a three phase only input. So I decided I'd use a small RPC I picked up to a while back. It's a small ARCO Roto-Phase model M. It's rated to start 3 HP max and a combined load of 9 HP, according to the nameplate. It should work. Everything appears to run as expected. It idles at 3 amps on L1 & L2. My capacitor bank consists of three caps and measures 13 amps. This all matches the manual.

    http://www.arco-electric.com/PDFs/IN...pdf?2021-04-17

    Does anyone have experience running a VFD off a RPC? How balanced do the voltages need to be?

    Unloadeed voltages between legs are:
    T1 & T2 247V
    T1 & T3 260V
    T2 & T3 275V

  5. #4
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    Re: Balancing rotary phase converter to run three phase VFD.

    I emailed Arco about a schematic and they this was the reply: "Because of the age of this unit, there is no internal schematic available. Pretty basic connection...T1 & T2 are the 1PH input to power the phase converter. T3 is the manufactured phase. Capacitors are wired and connected in parallel on the T2 & T3 connections."

    I have three 40 MFD caps in parallel with T2 and T3. No start cap. No balance caps between T1 and T3.

    I'm thinking I need some caps between T1 and T3 to balance all three legs. I really need to know how balanced the VFD is expecting the legs to be.

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  6. #5
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    Re: Balancing rotary phase converter to run three phase VFD.

    They are using the oil capacitors for starting.
    After the motor starts just turn off one or two capacitors the voltage will be right .
    If need more power later just turn on capacitor.

    Note You need all the capacitors to start the rotor phase . But do not need the capacitors after Starting.

    You can buy Starting relay witch is easier.
    I have diagram on this part.

    Dave

    Quote Originally Posted by forhire View Post
    I emailed Arco about a schematic and they this was the reply: "Because of the age of this unit, there is no internal schematic available. Pretty basic connection...T1 & T2 are the 1PH input to power the phase converter. T3 is the manufactured phase. Capacitors are wired and connected in parallel on the T2 & T3 connections."

    I have three 40 MFD caps in parallel with T2 and T3. No start cap. No balance caps between T1 and T3.

    I'm thinking I need some caps between T1 and T3 to balance all three legs. I really need to know how balanced the VFD is expecting the legs to be.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Quote Originally Posted by smithdoor View Post
    They are using the oil capacitors for starting.
    After the motor starts just turn off one or two capacitors the voltage will be right .
    If need more power later just turn on capacitor.

    Note You need all the capacitors to start the rotor phase . But do not need the capacitors after Starting.

    You can buy Starting relay witch is easier.
    I have diagram on this part.

    Dave
    I added the jumper with the blue crimp connectors between T3 side of the lowest cap and the rest of the caps. The jumper was broken when I got it. I think this is an accurate schematic. Obviously a potential relay would be ideal for unload the start caps. I'd be interested in your schematic with the relay.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Later I goto computer log on and send diagram

    Dave

    Quote Originally Posted by forhire View Post
    I added the jumper with the blue crimp connectors between T3 side of the lowest cap and the rest of the caps. The jumper was broken when I got it. I think this is an accurate schematic. Obviously a potential relay would be ideal for unload the start caps. I'd be interested in your schematic with the relay.

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    Re: Balancing rotary phase converter to run three phase VFD.

    I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.

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    Re: Balancing rotary phase converter to run three phase VFD.

    That about what should be if capacitors are balanced.
    No load should balanced with out any capacitor.
    Sound like yours has a start relay too.

    They run real big AC by balancing the capacitors at load using 3 phase on single phase.

    Dave

    Quote Originally Posted by M J D View Post
    I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Quote Originally Posted by M J D View Post
    I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.
    As originally configured, without the missing jumper, on just one 40 MFD capacitor, my unit ran fairly balanced. I added the jumper after Arco told me all three capacitors should be parallel to T2 and T3. It's quite possible the additional two caps would only be required to maintain balance under higher loads. The unit started and ran fine with one cap. With all three caps hooked up the amp measurement is 13 amps, the same value listed in the manual.

    Is it possible that there would have been a switch to enable the additional capacitors for startup in place of the jumper I made? There was a broken jumper in the enclosure. Of course I bought it from a guy that never used it so I'm thin on details.

    I would really prefer to get the voltages within 5 or 10 volts. I think it's definitely doable. I think I'll play around with the configuration and see if I can get it dialed in.

    I found this schematic that suggests using caps on each leg. I'll need to read through the whole page to wrap my head around the math later tonight. Is there a reason most schematics only show caps on T2 & T3?
    http://www.waterfront-woods.com/Arti...econverter.htm

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    Re: Balancing rotary phase converter to run three phase VFD.

    Log on to my laptop
    This is a simple way for three phase.
    I could not upload to book it is to big.
    note there are two page one is PDF file zip

    Dave


    Quote Originally Posted by forhire View Post
    As originally configured, without the missing jumper, on just one 40 MFD capacitor, my unit ran fairly balanced. I added the jumper after Arco told me all three capacitors should be parallel to T2 and T3. It's quite possible the additional two caps would only be required to maintain balance under higher loads. The unit started and ran fine with one cap. With all three caps hooked up the amp measurement is 13 amps, the same value listed in the manual.

    Is it possible that there would have been a switch to enable the additional capacitors for startup in place of the jumper I made? There was a broken jumper in the enclosure. Of course I bought it from a guy that never used it so I'm thin on details.

    I would really prefer to get the voltages within 5 or 10 volts. I think it's definitely doable. I think I'll play around with the configuration and see if I can get it dialed in.

    I found this schematic that suggests using caps on each leg. I'll need to read through the whole page to wrap my head around the math later tonight. Is there a reason most schematics only show caps on T2 & T3?
    http://www.waterfront-woods.com/Arti...econverter.htm

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    Re: Balancing rotary phase converter to run three phase VFD.

    I saw a series of good videos on YouTube about using different capacitors, adding more, etc. to even out the legs. The guys channel went by the name " sbirdranch". 3 parts I believe, where it shows how he did it. After watching I came to the conclusion that it's was way easier and probably in the long run cheaper, to simply buy an existing proven unit.

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    Re: Balancing rotary phase converter to run three phase VFD.

    It might be easier, but not as much fun, to change the VFD to one that is 1 ph in 3ph out.
    ---Meltedmetal

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    Re: Balancing rotary phase converter to run three phase VFD.

    Quote Originally Posted by Meltedmetal View Post
    It might be easier, but not as much fun, to change the VFD to one that is 1 ph in 3ph out.
    I totally agree with this,,
    I have two VFD's, one on a drill, the other on a lathe.



    The way they "sense" voltages, and amperages, excess loads, etc,,, I doubt that a converter could ever satisfy its input needs.

    More than likely the 3-in, 3-out VFD will shut down when the voltage variations are seen coming from the in-house created 3 phase electricity.

    Those single to 3 phase converters are designed to get a 3 phase motor to rotate, in an EVER SO CRUDE method, not feed an electronic device.
    The three phase motor will rotate, and simulate operation,, it in NO WAY comes close to an accurate operation.

    The motor will drill holes, or allow a cutter to make a pass on a lathe.
    The inverter would never produce an oscilloscope accurate 3 phase output.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Quote Originally Posted by Meltedmetal View Post
    It might be easier, but not as much fun, to change the VFD to one that is 1 ph in 3ph out.
    I suspect you are correct.

    Quote Originally Posted by SweetMK View Post
    I totally agree with this,,
    I have two VFD's, one on a drill, the other on a lathe.

    The way they "sense" voltages, and amperages, excess loads, etc,,, I doubt that a converter could ever satisfy its input needs.

    More than likely the 3-in, 3-out VFD will shut down when the voltage variations are seen coming from the in-house created 3 phase electricity.

    Those single to 3 phase converters are designed to get a 3 phase motor to rotate, in an EVER SO CRUDE method, not feed an electronic device.
    The three phase motor will rotate, and simulate operation,, it in NO WAY comes close to an accurate operation.

    The motor will drill holes, or allow a cutter to make a pass on a lathe.
    The inverter would never produce an oscilloscope accurate 3 phase output.
    The voltage sense on the VFD is really my concern. I know my Allen-Bradley VFDs cut out at 275V. I'd really like experience of someone running a CNC machine with a VFD driven spindle from a RPC. In my reading when running a CNC from a RPC they oversize the idler. It's quite possible that this RPC is simply too small and crude to maintain balance across phases and to minimize phase shift. Everything in the CNC control is single phase aside from the VFD. I know that I could change the VFD, and I still may do that, but I was hoping to run it with junk I had laying around. It might be fun to look at the output with the oscilloscope.

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    Re: Balancing rotary phase converter to run three phase VFD.

    The best converter is a motor generator type. It no more than a single phase motor driving a 3 phase motor.

    It is basically a direct couple together motors the 3 phase is connected t1 and t2 to 240 single phase. The generator only needs to generate the third leg.

    Dave

    Quote Originally Posted by forhire View Post
    I suspect you are correct.



    The voltage sense on the VFD is really my concern. I know my Allen-Bradley VFDs cut out at 275V. I'd really like experience of someone running a CNC machine with a VFD driven spindle from a RPC. In my reading when running a CNC from a RPC they oversize the idler. It's quite possible that this RPC is simply too small and crude to maintain balance across phases and to minimize phase shift. Everything in the CNC control is single phase aside from the VFD. I know that I could change the VFD, and I still may do that, but I was hoping to run it with junk I had laying around. It might be fun to look at the output with the oscilloscope.

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    Re: Balancing rotary phase converter to run three phase VFD.

    It is in the book I have.
    My self I used both types capacitor start and motor generator. The motor generator give better stable power .
    I have put both on a oscilloscope under load.
    Just like 3 phase from the power company.

    Dave

    Quote Originally Posted by forhire View Post
    I suspect you are correct.



    The voltage sense on the VFD is really my concern. I know my Allen-Bradley VFDs cut out at 275V. I'd really like experience of someone running a CNC machine with a VFD driven spindle from a RPC. In my reading when running a CNC from a RPC they oversize the idler. It's quite possible that this RPC is simply too small and crude to maintain balance across phases and to minimize phase shift. Everything in the CNC control is single phase aside from the VFD. I know that I could change the VFD, and I still may do that, but I was hoping to run it with junk I had laying around. It might be fun to look at the output with the oscilloscope.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Run capacitors should be 12 to 16 uf per HP.

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    Re: Balancing rotary phase converter to run three phase VFD.

    The rotor phase converter company is using the oil capacitors for starting too.

    Great for make the converter hum

    Dave

    Quote Originally Posted by arcflash View Post
    Run capacitors should be 12 to 16 uf per HP.

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    Re: Balancing rotary phase converter to run three phase VFD.

    I made my own 10hp 240v 3ph rotary converter using that same type of diagram with a potental relay too. 10 hp baldor motor and a 2ft by 18in cabinet with the starters and caps in it. I used it to run my MCV550E leadwell cnc VMC. The leadwell has a FR-se drive for the 7.5hp spindle motor and 4 TRA41 axis drives for the axis's. Had no problems at all running it. I balanced it by adding and subtracting capacitors from between the 3 phases. I sold it a long time ago as i moved and installed real 3 phase. I think i had around 246, 243, and 238 for balance. It needs to be balanced while running the machine too as loads will change the phases around. The VMC has a transformer in it too that acts like a line reactor to smooth out spikes and dips a little bit. I had 4 converters total for my machines and balancing them always reminded me of the college days doing vector diagrams and lead lag stuff.

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    Re: Balancing rotary phase converter to run three phase VFD.

    Quote Originally Posted by ferrret3238 View Post
    I made my own 10hp 240v 3ph rotary converter using that same type of diagram with a potental relay too. 10 hp baldor motor and a 2ft by 18in cabinet with the starters and caps in it. I used it to run my MCV550E leadwell cnc VMC. The leadwell has a FR-se drive for the 7.5hp spindle motor and 4 TRA41 axis drives for the axis's. Had no problems at all running it. I balanced it by adding and subtracting capacitors from between the 3 phases. I sold it a long time ago as i moved and installed real 3 phase. I think i had around 246, 243, and 238 for balance. It needs to be balanced while running the machine too as loads will change the phases around. The VMC has a transformer in it too that acts like a line reactor to smooth out spikes and dips a little bit. I had 4 converters total for my machines and balancing them always reminded me of the college days doing vector diagrams and lead lag stuff.
    Thanks. The machine has a large transformer and a line reactor. I have the machine running off the RPC and it appears fairly balanced. After a fair amount of messing around this afternoon, including loading it with a fair sized motor, I decided the only thing I could really do is simply try it. The VFD should complain if it was too unbalanced. The control was booted on single phase simply to make sure it all lit up. After clearing the typical e-stops and such I hooked up the RPC. The VFD does show the voltage fluctuating a few volts, but it appeared to tolerate it. The machine homed and jogged as expected. I warmed up the spindle for about an hour. Spindle motor runs cool as does the RPC idler. Draw on the single phase input is around 5 amps. Draw on the machine side is measuring around 2 amps per leg. It appears to be fairly happy. I'll need to take some measurements while cutting. The true test will be to see how reliable it is in operation.

    The machine is an old Multicam CNC router with a 25"x25" travel. My neighbor picked it up a few years ago. We've been talking about getting it hooked up ever since he moved in. I offered to roll out an extension cord so we could at minimum test it. He's pretty excited to see it run.

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    Re: Balancing rotary phase converter to run three phase VFD.

    It's all buttoned up. We put it on a manual starter and tucked the idler under the router. The table is off the blocks and leveled. It's working great. We ran it through its paces most of the day and it worked flawlessly. We still need to sort a mount for the control interface and hookup a PC.

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  26. #23
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    Re: Balancing rotary phase converter to run three phase VFD.

    Yours is buttoned up (good Job) Mine is just starting.. I have 15 rotary, and 5hp in my mill, but need to get around a 30 hp total.. Just just to add as needed to my 15 rotary. Maybe build a use a mag starter extra run caps to balance the load amps/volts if way out.. Here is my project.. $250 welder, and these are very modern 3 phase transformer units.. I have no issue running 30 amps of 3 phase to my three phase only cutmaster 60i but this thing doubles it's draw..

    I just need to run over to Springfield Oregon and see my buddy there. He has extra motors out in his yard.. Also runs totally on Solar with about 25 guys in his shop at certain times.. Many big linchpin 3 phase units like this Esab.. Quite a setup really.

    These Esab are plastic case models so pretty late model stuff..Don't worry it has a hook in top to move so it's still the real deal..
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  27. #24
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    Re: Balancing rotary phase converter to run three phase VFD.

    All solar in Spingfield is pretty impressive.

    I have three phase here at the shop. Years ago, before installing three phase, I picked up a Lagun FT1 mill, that had been converted to CNC, from a guy that had it in his garage without three phase. He figured he'd run it off an RPC but never got around to it. As a result, I picked it up cheap. After I bought it I was thumbing through the VFD manual and realized I could run it off single phase. I ran it that way for a couple years before installing a new three phase service in the shop.

    I have a 10 HP motor I've been planning on using for a RPC at the farm shop. I rebuilt the motor about 10 years ago and still haven't gotten around to finishing it. I've been looking looking at on the the pre-made controllers.

    Dave sent me a manual... I might build my own controller once I digest all the information.

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    Re: Balancing rotary phase converter to run three phase VFD.

    I bought my box from a guy on Ebay.. I ordered it for a 10hp I thought I was getting, but it turned out to be a 15hp motor.. I run my Cincinnati #2 and three other inverter welders for different reasons. My Lorch/Esab for extra output when ran on three phase. Seems to work fine, and the Lorch won't turn on if it sees something it does not like in the power input. The mill has three motors. one is a smaller pump motor, but the knee is 2 hp, and the spindle is 5hp.. Just made a switch to run just the main 5 hp, and just tunes the large pulley when stitched over for rotary work.. Still not enough for the Esab CV-353 . I bit a 10, and a 15 would make it function for my needs.. I have a feeling the 15 hp setup would fire off a pretty decent motor being unloaded.. 100 line limits my little shop, but I could get 200 amps to it if needed. I just want it reasonable to run the Esab, and going over a 100 amps to run the thing is really where I rather be.. I have inverters to have inverters anything I really need to weld with, but just interested in the older stuff to get it to work. I just want a 3 phase transformer mig unit, that will be with me forever..

    I local guy i traded my Cutmaster 60i I had run his monster cnc lathe off of his 25hp rotary .3 phase is right there too I got my cool slotter from him in trade.

    Anyway, the guy is in Gaston, Oregon, I just drove out, and picked up the box by paying a bit of different in price for the higher powered control box setup.. Balanced out nice.. He has good support too..They have went up a bit, but maybe direct dealing might get it down a bit?

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