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  1. #1
    Join Date
    Jan 2006
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    Default 2hp phase converter up and running!

    Hello all,

    I have been mucking around with phase circuits in the shed this morning, and thought I would share my prototype phase converter.
    The pic below is of a 2hp delta wired 3 phase motor which I start with 100uf capacitors with a 15amp momentory switch. The balance capacitors give me 237v, 231v and 228v from phase to phase, which I am very happy with. The motor starts instantly and runs quietly. Anyway, this setup is just so that I could help myself to get my head around the circuitry. I'll pull it apart after breaky, and get started on the main project further below.....






    The grand plan.....


    I plan to get this 10hp motor going with a single phase pony motor, to keep the starting current low, and then power my shop from that. This motor is new/never used, and I picked it up at auction for $10.00
    I have a 1hp 1~ motor laying around somewhere, so I figure I should be able to get the whole shop wired with motor protection etc etc for the 3~ circuit for under $200.00.





    I will then fit the 2hp 3~ motor to my lathe and use a VFD that I have
    laying around.



    Anyway, that's my Sunday project.

  2. #2
    Join Date
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    Default

    Fossil, nice work on the prototype. That big motor worries me a bit though...I'm not sure that a delta wound motor works as a phase converter. I haven't made one that size, mine have been star-wound 5 hp versions, and only recently heard that star winding is required. I haven't done research into the bigger sized motor conversions, but I can point you to some links.

    The other thing is to use two smaller rpc motors on two separate circuits, but I know that's not what you want.

    I'm getting a new 7.5 hp Leeson motor tomorrow, but I have to pay closer to retail...nearly $60.00, or 10%, in my case

    Greg

    BTW, what is that lathe you are running? Looks the goods..
    Last edited by Greg Q; 8th Jul 2007 at 12:59 PM. Reason: senior moment

  3. #3
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    Default

    Hi Greg,

    Thanks for the comments. I have been looking at these things for a few years now, printing off the U.S based info for quiet reading in my bathroom down time.

    I have been quite confused at times, trying to get my head around the theory, especially as it applies to our Aus power with active 240v and neutral, as apposed to the US 120 + 120v split or dual phase active supply. I wired delta because I don't want the expense of a step-up transformer to get 415v for star wound motors. If I am correct, delta wound RPC will give me close to 240v between phases, which means that I have 138v from delta point to neutral. 3x 138v giving 414v. Most of the 3~ motors that I have are the dual voltage wye/delta type, so I figured I would just wire them all delta, and dispense with the transformer.
    Anyway..... perhaps I have just disclosed my ignorance, so if you can set me straight, that would be appreciated.
    I have 60amps single phase to my workshop at the moment, so I was hoping to get the 10hp started with the pony motor, and then the 10hp will have enough enertia to start the smaller 3~ motors without too much of a current spike.

    The lathe is an old IXL Invicta. I restored it a few years ago, but haven't got around to finishing the stand and chip tray etc. It has back gears, and a powered cross slide as well as power londitudinal feed. I am looking for more change gears for it though. I am severely limited in my thread cutting capabilities with the few gears that I have.

    Thanks again for the reply. Mabey when you get your new motor we can share building progress ideas??

  4. #4
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    Default

    I have been re-reading a lot of the information lately too. Wireless means I don't have to print out to use the library

    I was reviewing the articles that I have...I think that I may have formed the impression about the delta wound motors from a line in John Hanrahan's paper-but it only mentions that the test data he provides is applicable to wye (star) motors. One knowledge base article claims that delta is better, but I don't trust internet information unless corroborated by a trusted source.

    My next converter is going to be a two-phase input (because I have 2 separate phases in my panel). My sparky is going to run a disconnect to separate 30A breakers, 6mm wire conductors to the rpc control box. Real overkill stuff. I have to do more research now, as this is breaking new ground, and I'm only going this route because I can't seem to find a big 240/415v transformer to step-up a true single phase 240v A + N input.

    One other aspect of the rpc to remember is that you only need maybe 1.4 X the rated power of your largest load motor...after it's running you can add load to at least twice your rpc's nominal rating. For my woodworking gear, that's 4 + 3 + 3 hp (saw+dusty+compressor) concurrently on a single 5 hp rpc. (240v). Luckily all of my existing 3 phase load motors are dual voltage.

    I'm was thinking about a vfd for a lathe, but now I don't need the variable speed, so a small rpc will be all I need for a metalworking machine circuit. If/when I get a mill it's motor voltage will probably be 415v, so I expect that will be the limiting factor.

    Greg

  5. #5
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    Default

    Oh, btw...I bought all of my three phase power points and plugs on ebay, paid on average $25.00 each pair. I think they retail for $120 for the power point alone. Three phase stuff seems to always go for pennies on the dollar, doesn't it?

    Greg

  6. #6
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    Default Ok Coming in really late here - could you tell me about this project of yours?

    Hello Fossil

    Tom's the name & I'm new to forums in general & certainly new to this thread.
    What is an RPC? I'm thinking the last two letters stand for Phase convertor.
    Also what the hell is a phase convertor & what does it do?

    I'm a Fitter & machinist & I guess I'm on here wanting to pick someone's brains about welding in general & specifically Tig welding.
    Being a tradesman I've worked in idustry since I left school & have used a fair range of industrial machinery.
    By the looks of things Fossil I haven't been around as long as you, I'm 33.
    But hopefully I have something to contribute that may help yourself or someone else at some stage.

    I was hoping some of you might know where I can find a tutorial on the web regarding Tig welding basics.

    I found a good Stick Welding tutorial at www.aussieweld.com.au if that's of any help to someone else.

    Thanks

  7. #7
    woodcutta Guest

    Default

    Fossil

    The voltage from phase to phase is not by addition. The reason is the 120 degree phase shift between windings. To calculate p/p it is the phase to neutral voltage X square root of 3 (1.73 close enough) Therefore a phase to neutral voltage of 138 volts will give you 239 volts phase to phase

    woodcutta

  8. #8
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    Woodcutta, if you have another look at what Fossil wrote, you'll see that you and he agree on the p-p and p-n voltages.

    For the benefit of other readers, Fossil is going to be making 240v three phase, but since all of his load motors are dual wound he'll be ok with that-just needs to connect terminals accordingly.

    Many motors that we see on machines that will fit in our sheds can run on 240volts. I happen to be getting a machine that needs 415 volts, and a motor swap might not be possible, hence my own next rpc project may be higher voltage.

  9. #9
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    Dodgy brother

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    Default

    Gday Tom, & welcome.

    Probably best starting a new thread with your welding questions, you will catch a wider audience.

    Just open the Metalwork Forum main page, and click on the New Thread button & follow yer nose.


    Cheers..................Sean


    The beatings will continue until morale improves.

  10. #10
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    Quote Originally Posted by tomhowell View Post
    Hello Fossil


    What is an RPC? I'm thinking the last two letters stand for Phase convertor.
    Also what the hell is a phase converter & what does it do?

    Thanks
    Hi tom, and welcome. RPC stands for Rotary Phase Converter. It uses a three phase motor as a kind of generator. Starting the three phase motor with just a single phase input is accomplished by either wiring in a bank of start and run capacitors, or spinning the motor with another, smaller motor.

    Leads are connected to the rpc windings, as induced current in the non-powered phases will provide three phase power. Nothing is quite that simple of course, and there are many refinements possible to balance the voltages produced, and to time the start cap cycle. (Since a three phase motor is used as the basis of the rpc, there are no built-in speed sensitive switches to control start/run caps like there are in a single phase motor, for example)

    There's a couple of weeks worth of reading on the net, much of it useful;-)

  11. #11
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    Default

    Thanks for answering Toms question Greg. I have been busy on a job today, and have only just got home.... Rained out.

    I didn't do any work on the large converter yesterday as planned, but decided to get my drill press going. It has a 3/4hp 3~ motor that is wound wye. I had to do some delicate brain surgery on the motor windings to convert it to delta. I looked around for the 1hp motor that I new was hiding somewhere. I am a bit of a messy bugger, so it took a bit of searching to get my hands on it. Anyway, it's not 1~ but a 1.5hp 3~ so using it as a pony motor is probably not worth the effort. I now intend to use the 1.5 hp 3~ motor that I have for my VFD lathe setup. I will use the 2hp that is shown above, as a pony motor to get the 10hp going. I intend to set up the circuit so that I can use the 2hp as a rotary converter for my smaller motors... (lathe and drill press) and then I won't need the big idler running all the time. I can switch the big idler in when I run my big saw and stroke sander, both of which will be 5hp 3~ when I am finished. I need to turn up a decent disconnect for a large 1 way bearing clutch that I have, which will neatly facilitate phyisical connection/disco of both the converter motors.

    Well.... that's wher I am up to.

    P.S. woodcutta. You are spot on. That is what I was trying to say. I probably didn't word it very well. I was basing my statement on what was in my head, which wasn't trig. When I was trying to work it all out for myself, I drew a delta triangle to exact scale, and physically measured the voltage with a scale rule, from delta point to neutral. So that was the basis for my wording.

    Have a good evening all.

    Fossil

  12. #12
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    Hi guys
    I am very interested in building an rpc as the number of requirements for 3 phase is increasing and the $26K quote for 3 phase was prohibitive. Do you have any good web sites or reference info - I am an old tech trained in electronics and electrical so am comfortable with the technical side of things. 3 phase motors are cheap second hand and so are power points etc if you have a good recycler nearby. Don't know of any cheap supply of big caps though.

    To date I have gone to Honda power for a couple of larger applications - 9HP to 18" thicknesser (very heavy duty type that 3HP single phase would not even budge) and a saw bench for ripping big stuff. Honda's start with one pull nearly always so no real issue except for a bit of noise and shed doors being opened at both ends. I have a big metal lathe running 3HP single phase but would prefer 3 phase for the torque.


    Any help greatly appreciated.

    Bill

  13. #13
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    Hi BB...

    You can start your searching reading the many posts here:

    http://www.practicalmachinist.com/ub...p/forum/3.html

    or any one of the many places that Google will take you. You can get yourself three phase for a couple of hundred if you are very frugal, but don't skimp on any of the safety features that the better designs have. Proper wiring, disconnects, circuit breaker and thermal overload protection all need to be considered as part of a balanced design.

    I sourced all of my three phase distribution equipment and single phase panel breakers on eBay for approx 20% of the new price. That can add up to a $500 savings pretty quickly, but you may have to shoot your sparky an extra hundred or so to keep him happy.

    You can get good three phase motors for scrap value...about $10/h.p. is typical. A 7.5 hp three phase motor may be as big as you'll find for an idler motor. This will then start a 7.5 h.p. max starting load, but you can run a higher total load if its composed of a few smaller motors, started sequentially.

    Have fun reading

  14. #14
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    IMO you are far better off price wise getting your caps from the U.S.

    Just make sure they are rated for a suitably high enough voltage for your application.
    When you have read plenty and have yourself up to speed with most of the variables, I will send you a schematic I drew up of the system I have just installed if you like.
    I have to go away for a few days so won't be able to respond till then.


    As Greg says.... have fun reading.

    Just remembered..... the schematic is on the PM site that Greg gave you. I have the same username there.
    You can substitute the pony motor with start caps if you have a large enough 1~ supply for your application.

  15. #15
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    Default

    Thanks guys

    Caps from US sounds good idea if as you said I can get the voltage rating and with the good exchange rate at present even better. Yes Fossil I have just upgraded my single phase with 16mm cable all the way from feed to the sheds plus a new main board. The sheds have fresh wiring anyway. Whatever I come up with I will have to time share with SWMBO for power as she is into glass slumping, casting etc with an assortment of electric kilns that I have restored. They are wired for only one active at a time but happily running 25A resistive load with minimal voltage drop to the mains.

    Would love to get a copy of your circuit diagram etc when you return.

    Thanks again

    Bill

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