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Rotary Phase convertor on a budget...my first tech week tech!!

Discussion in 'The Hokey Ass Message Board' started by 333 Half Evil, Apr 15, 2010.

  1. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    Ok, I'm not much of a typer, speller, nor am I an electrician, but I'll do my best to walk you guys through the building of a low budget rotary phase convertor. I've seen a lot of posts on several board about phase convertors...and swapping motors on equipment to single phase so one doesn't have to spend money on a phase convertor. I've built a few of these over the years after working in a machine shop that was in a garage behind my bosses house that was using a rotarty phase convertor in it. That shop had 3 lathes, 2 of then were small/medium size lathes with 2hp motors, and big LeBlonde 5hp lathe and 4 bridgeports, 3 2hp ones and one 1 1/2hp. This entire shop was run with a 10hp torary phase convertor built exactly as the one I built here in the following pics.

    A little input about the rotary phase convertors. The rotary phase convertors can run 90% or more of the convertor motors hp rating. This is to say that a 10hp rotary phase convertor can run 9hp worth of load or even more, but I use 90% so I know I'm under the actual load. A rotary phase convertor can "start" only 75-80% of the convertor motors hp rating, meaning that a 10hp rotary phase convertor can start a 7 1/2-8 hp single load. I always use 75% starting ability to be on the safe side as well. If you have a piece of equipment that has a 2hp motor on it, a 3hp rotary phase convertor will work fine for you. You can also be running a load on the convertor and still start another load if you need. I do not know exactly how much load can be running and how much you can start, all I know from experience is that the shop mentioned above had a 10hp rotary phase convertor and we could have three of the bridgeports running when the 5hp LeBlonde lathe was started. That would be 6hp running and 5hp starting on a 10hp rotary phase convertor.

    So, now onto the building of your budget rotary phase convertor. The following is a list of what you need:

    1) a used 3 phase motor for the convertor(voltage and hp rating of your need) You can use a multi-voltage motor 208-230/460 if that is what you find. You cannot use a 460 only if you do not have 460 volts to supply it.

    2) a smaller electric motor for a "starter". The one in the pics is a 110 volt 1hp, but I've used a 110 volt 1/2hp on a 10hp rotary phase convertor.

    3) a belt to connect the starter motor to the convertor motor.

    4) Electrical shot-off box. It is up to you on how you want to fuse your unit. If you only want to rely on the breakers in your main electrical box, that works, or you can get a fused cut-off(on/off) box.

    5) Wire. You will need a line of single phase 230 volts to feed the 3ph convertor motor and you will need wire to carry the 3ph power from the convertor to your shop or equipment.

    6) something to mount the two motors on...board, steel plate, channel iron, cart. Whatever you want!!!

    NOTES: You can use new motors if you want, but being a budget deal I use used motors that I've bought cheap at auction sales. The 7 1/2hp multi-voltage 3ph motor used on the convertor in the pics was $68.00 The 1hp 110 volt motor used as a starter was $15.00 both bought on a auction sale. I've got less that $100. total in the phase convertor in the pics. The cart it is on, was an old welder cart that the guy had from his first, small wire welder.

    The starter motor has to be able to spin the convertor motor as fast as the rpm rating of the convertor motor. If the convertor motor is 3450, then the starter motor has to be 3450, but if it is slower, you can use pulleys to change to "ratio" of the two so it will spin fast enough. It is not a problem if the convertor is spinning faster, but it has to spin at least as fast as the rated rpms. If the convertor motor is not spun fast enough, when you turn the supply power on to it it will just stall and make a buzzing sound!!! Been there done that!!!


    The starter motor is needed to get the convertor motor up to speed BEFORE power is supplied to it. This is important. You have to have the convertor motor at speed before you put power into it or it will stall. The rotary phase convertors that you see for sale, and are kinda costly use capacitors/coils to "jump" the 3rd leg of the convertor motor so it will start on it's own. That is most of the reason for the cost involved with those. Once they capacitors/coils have the motor started, they drop out of the circuit and the phase convertor continues to run on its own. The phase convertor I'm showing you how to build uses a small starter motor to get the convertor motor up to speed, then power is supplied to the convertor motor and it will now run. Once the convertor is up to speed, power is supllied to it, you can turn off the starter motor and the convertor will continue to run on its own, creating the conversion from single to 3 phase power. I usually remove the belt from the convertor motor and starter motor, but you do not have to.

    Depending on the color of wire you use, I kind of made my own code to label the wires to make it easy to follow. My 230 volt wire that I used to supply the phase convertor was 3 wire that had black, white, and green wires. The black and white are hot(110 volt legs) and the green is common/ground. Some people call it common some call it ground...

    The "code" I use for these wires are as follows:
    Black is I1
    White is I2
    Green is I3

    For the 3phase power coming out of the phase convertor I used a four wire coard that had black, white, red, and green. Black, red, and white ALL carry power, they are the hot "legs" from the convertor. The green is common/ground.

    The "code" I use for these are as follows"
    Black O1
    Red O2
    White O3
    Green/ground O4

    The supply power is routed into a cut-off(on/off box) to be able to stop/start the phase convertor. From this box it will go to the 3ph convertor motor. The 3ph motor should have a wiring tag on it that shows what wires are needed to be connected together. If it is a multi voltage motor like the one I am using it will have a Low voltage(208/230) diagram as well as a high voltage(460) diagram. Use the one that fits your voltage supply. I'm using 230 volts as most of you will have too. The tag shows low voltage wiring to be as follows:

    The wires on the motor will be numbered 1 through 9.

    4,5,6 get connected together

    3,9 together

    2,8 together

    1,7 together

    Now, the supply power gets connected as follows:

    Black I1 to 3,9
    White I2 to 2,8
    Green I3 to the ground screw.

    Now the 3phase output wires are connected as follows:

    Black O1 to 3,9,I1
    Red O2 to 2,8,I2
    White O3 to 1,7
    Green O4 to ground screw

    All the wires in the box on the convertor motor will now be as follows:

    4,5,6 together
    3,9,I1,O1 together
    2,8,I2,O2 together
    1,7,O3 together

    You now run the 3 phase power from the convertor to you equipment. You can either "hard wire" it for a permanent type wiring or you can use plugs on the coards to make a "mobile" type. The one in the pics is a "mobile" unit because the guy has two buildings with only 1 piece of equipment in the one, and a mill and lathe in the other. He is the only one using it, so he doesn't need to have it hard wired. He just plugs the supply coard into his welder outlet, plugs in the piece in the piece of equipment he is going to use and away he goes.

    When you have your convertor finished, and you go to use it, if the piece of equipment runs backwards, all you have to do is revearse ANY TWO wires of the 3 phase outputs. This meaning, on you equipment the wires you connect to the black,red, and white output wires just take any two of them and revearse them. It can be swapping the black and red, the black and white, or the red and white and now your equipment will run the correct direction.

    For the starter motor, most guys just have the starter motor on a cord and they just plug it in to get the convertor motor up to speed, then unplug it once they switch power on to the convertor motor. On the convertor in the pics, I just used one "leg" of the 230 volt supply power for the supply to the starter motor. I pulled the power from the "in" side of the cut off switch, that way I have power for the starter motor before the power is on to the convertor. It is run through a on/off light switch. Once the guy plugs in the convertor(with the cut-off(on/off) box OFF, he just turns the starter motor on by using the light switch, once it is up to speed he then switches the cut-off(on/off) box ON and the convertor is mow running. Now he just turns off the power to the starter motor and he has 230 3phase power to run whatever piece of equpment he needs.

    I normally do not leave the belt on...no need for the starter motor to just be free wheeling while the phase convertor is on. You do not have to do this, it is just something I do. I make it easy to remove the belt be having the starter motor on a hinge so I can pivot it up to loosen and remove/install the belt. The weight of the motor is enough to keep the belt tight as all it has to do is turn the convertor motor over to speed. If you notice, there is no pulley on the shaft of the convertor motr as it really does not need one as all it does is free spool until up to speed. The starter motor we used on this one was actually from a belt sander, and we could not get the flat rubber pulley off, so I just ground a notch in it so the belt has a groove to ride in. Any normal pulley will be fine!!! If you are going to leave the belt on all the time, then maybe you should run pulleys on both motors.
     

    Attached Files:

    Last edited: Apr 15, 2010
  2. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    Hey guys, I cannot figure out how to get my pics in with my writing. So, I attached pics afterwards. I'm going to try and do some more pics to go along with it. Maybe I'll post a couple pics, and write what the pics are showing so it might make more sence. Like I said, I'm not much on how to post things, but I know this tech should help a lot of guys who want or need 3phase power and have a limited budget to work with. This phase convertor can be done usually cheaper than swapping motors on the equipment from 3 phase to single pahse. I'll try and get the pics figured out.
     
  3. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    BTW you could (if so desired) get rid of the starter motor by replacing it with START caps on the converter motor. A 3 phase motor will not START with only "2 hots" feeding it, but it will run (once spinning) with just those 2 legs. The Start Caps are used to MOMENTARILY "FLASH" that 3rd leg making the motor "think" it's seeing actual 3 phase for the startup. Once up to speed you can drop the caps out of the circuit. In addition you can also (somewhat) "balance" your outputs by adding RUN CAPS from L1 to L3 and L2 to L3 (L3 being the "generated" leg). There are some benefits to this, but it's NOT a show stopper if you don't want to do it.

    BTW - if you want to go BARE BONES - loose the start motor - loose the Start Caps and merely wind a rope around your converter motor (via a pulley of course) and give the rope a good YANK and after it's SPINNING apply the single phase power - it WILL RUN and generate (albeit a tad weak) that third leg. Personally I am too lazy for this method, but it will work!!!

    Nice Tech - BTW!!!
     
    Last edited: Apr 15, 2010
  4. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    This is just a quick drawing of how a rotary phase convertor would be if mounted flat on a board, plate, piece of channel iron, etc. It also has a drawing of wiring.
     

    Attached Files:


  5. Thanks for the post! a keeper for sure
     
  6. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    Here is a drawing of the wiring schematic. Please forgive the poor writing and drawing on my part. And the pictures suck too...I know.
     

    Attached Files:

  7. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    Hey HemiRambler, I know about adding the caps, but around my area I never see them on auctions, and the price of new ones is kinda high. So I go the cheaper route of a small used motor to get it started/spinning. You are right, a rope wound round the pully/shaft and pull does work, my first one was that way...takes one hell of a yank on that rope...and I too am just to lazy anymore for that. Thanks for your added input, it is always appreciated.
     
  8. noboD
    Joined: Jan 29, 2004
    Posts: 8,458

    noboD
    Member

    333, a neighbor/friend built my first converter just like that, worked great. Good tech post. I think he said the 3 phase motor has to be a Delta motor, not a WHY or Y. Is that right?
     
  9. HemiRambler
    Joined: Aug 26, 2005
    Posts: 4,208

    HemiRambler
    Member

    Half Evil, Just some thoughts from the Peanut Gallery!!!;-) I agree those caps can add up pretty quick $ wise - so I buy them CHEAP at the electronics surplus place. Rule of thumb here is: IF they are ROUND they are generally START CAPS - if they are OVAL they are genrally RUN caps. I always avoid the PCB ones - the good ones are usually marked "no pcb's" - also it's not problem using ones with a HIGHER rated voltage - so I grab what ever I can get my hands on and then adjust the value by hooking them up in parallel or series - but the value does "add" wierd depending on how you do it (I won't even attempt to explain that - I just follow the examples on the web).

    Another food for thought comment - getting a 3600 rpm "idler" motor is better if you are starting 3600 rpm LOAD motors - ask me how I know!!!!!
     
  10. 333 Half Evil
    Joined: Oct 16, 2006
    Posts: 1,440

    333 Half Evil
    Member

    noboD,
    Good question. Honest answer = I do not know! I am in no way an electrician. To be honest, whenever I've done any of these, I either have the guy find a 3ph motor that fits his requirements or I'd look for one. Whenever I've bought any I just looked at the tag and made sure it was at least a 230 volt or a multi voltage 208-230/460 and made sure the it had a mounting base and a shaft to run a belt or pulley on.
    If that is a true statement, about the delta and not a WHY or Y motor, I have been very lucky and never run into a motor that would not work. I hope if somebody knows for sure that they will chime in and comment. Thanks for the tip/question.

    EDIT: a quick google search showed the WHY/Y to be WYE or Y. More when I find it....

    EDIT #2: The specific voltages and their relationships with ground or a possible fourth "neutral" wire depend on the exact type of transformer arrangement that supplies your home or business. In the standard "Delta" arrangement (which you can find discussed at sites dealing with power distribution), the voltage differences between any pair of the three phases is typically 240 VAC. In the standard "Wye" arrangement, the typical voltage difference between any pair of phases is 208 VAC and the voltage difference between any single phase and ground is 120 VAC. And in the "Center-Tapped Grounded Delta" arrangement, the voltage difference between any pair of phases is 240 VAC and the voltage difference between a single phase and neutral is 120, 120, and 208 VAC respectively (yes, the three phases behave differently in this third arrangement).

    If you run a single-phase 220 VAC motor from two wires of a Delta arrangement power outlet, that motor will receive a little more voltage (240 VAC) than it was designed for and if you run it from two wires of a Wye arrangement outlet, it will receive a little less voltage (208 VAC) than appropriate. Still, the motor will probably run adequately and it's unlikely that you'll ever notice the difference.

    Not sure if it makes a difference.
     
    Last edited: Apr 15, 2010
  11. the other me
    Joined: Jun 21, 2007
    Posts: 387

    the other me
    Member

    Yo Evil...how ya been man. I've been absent for a few years. Glad you are still hangin out. Man, if you even figure out how to do writeups like these, man you'll have some sweet posts for sure!!! Just givin ya sum sheite dood. You know me!!!! Anyhow, that old phase convertor ya made for me is still swingin along man. Guys, this shit works. I've got mine hardwired into the shop, so I've got several outs for 3ph and running a couple mils, lathe, and a 3ph welder. Evil helped me out with mine some 10 years ago or so...was an old 10hp motor a buddy that works maintenance at a assembly plant had changed out due to it having many hours use. It still was a working motor, but had to have it changed out due to age i guess. I got it for nuttin, Evil gave me ahand, and we just put it and the 1/2hp starter motor on a piece of 6" channel bout 2ft long. I have it located behing the wall in the compressor room. Just gotta thro the light switch for the starter motor, was a couple secs., thro the big 3ph box on turn of starter and shop is up n runnin. Good on ya fer posting a tech deal Evil...don't be shy man post up some more!!! Lateron dude!!!
     

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