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  1. #1
    RPMWFO is offline Plastic
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    Default Need three phase 440 from single phase 220

    New to the forum. I am looking at a used Bridgeport that has been retrofitted with a Acer E-Mill electronically variable speed head(3HP). The inverter for the machine requires a 440V, three phase power supply. My shop only has 220v single phase power.

    It appears I have two options:

    1. Change the inverter to one that accepts 220V single phase- expensive and potentially complicated(I would imagine).

    2. Use a single phase transformer to convert 220 to 440. Then use a rotary phase converter. Would this work? What size transformer would I need to use(7.5 KVA?)? Is it relatively safe to use used transformers that are available? Commercially new transformers seem to run about $500-600. Is it possible to use a step down transformer in reverse to step up the voltage? How complicated is the wiring going to be on this? Any downsides?

    Let me know what you guys think. I don't want to buy the mill if I can't get the power worked out. Looks like this is already going to set me back $500-1000 for option 2. The mill is in good shape and local. Not a lot of offerings in the area for used BP's.

    Thanks in advance.
    Pat

  2. #2
    peterh5322's Avatar
    peterh5322 is online now Diamond
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    "Use a single phase transformer to convert 220 to 440. Then use a rotary phase converter. Would this work? What size transformer would I need to use(7.5 KVA?)? Is it relatively safe to use used transformers that are available? Commercially new transformers seem to run about $500-600. Is it possible to use a step down transformer in reverse to step up the voltage? How complicated is the wiring going to be on this? Any downsides?"

    This would be my choice.

    A 460-to-230 transformer may be reversed and employed to increase 230 to 460.

    7.5 KVA should cost about $100, but if it is shipped by UPS that could add another $100, so DO try and find one locally.

    These will usually have taps on the high side (the 460 side) and a split secondary for 230 or 120.

    Wire the low side for 230 and 440, 460 or 480 will come out the high side, depending upon which taps are selected.

    An idler wired for 460 would be used for the RPC.

    The usual rules of thumb for calculating the capacitance must be modified as with twice the applied voltage, only one fourth of the usual capacitance is required.

    Also, the caps must be rated for twice the voltage, which is 500 for the starting cap and 740 for the run caps.

    You can use a Steveco 90-66 potential relay in the starting circuit if you place the sensitive coil across one-half of the idler.

    Schematics which describe all of these issues are found in the archives of thus Forum.

  3. #3
    DaveKamp is offline Titanium
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    Quote Originally Posted by RPMWFO View Post
    Change the inverter to one that accepts 220V single phase- expensive and potentially complicated(I would imagine)
    Pat
    Probably not as expensive and complicated as you might think... worst thing you'd run into was packaging... i.e. if the original drive was mechanically built into the head... your replacement might not physically 'fit'... you'd be putting it in a conventional exterior enclosure.

    There's three motor leads from the drive to motor windings. If the original drive used an encoder or tach input, there'd be two, three, or four small wires there... you'll have a start/stop and direction control (mebbie five small wires total).

    There's one other possibility...
    What IF... the internal inverter was capable of operating under single-phase power as-is? Might be hard to get manufacturer's data to support it, but some careful experimentation MIGHT prove it suitable to your needs on single-phase only. Running a (reversed) transformer MIGHT be all you need to try. Of course, a derating will likely be necessary, BUT, that may still be suitable, without the added complexity.

  4. #4
    k3vyl is offline Hot Rolled
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    Default transformer

    You could also use three 2.5 kva control transformers downstream of your converter.They are easier to handle and obtain.I know a fella that ran his 460V hardinge lathe off that setup.It may even be a good thing because of isolating the load from the neutral of the single phase supply.

  5. #5
    motion guru's Avatar
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    Another option would be to use a 230V rotary phase converter and then step up from there with a 3 phase 460:230 VAC transformer wired backwards.

    One advantage of this is that most transformers have adjustable taps and this allows you to balance phases a little easier. And it seems these transformers are available as surplus for less cost. We have picked up 3 transformers like this ranging from 7.5kVA to 30kVA in the last 2 months from $100 - $200 each

  6. #6
    Mike C. is online now Diamond
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    Yup, converter run through a step-up is the simple way. Been running that way for three years.

  7. #7
    RPMWFO is offline Plastic
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    Bought the mill. Now I have to figure out how to get it wired up to run.

  8. #8
    RPMWFO is offline Plastic
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    Quote Originally Posted by motion guru View Post
    Another option would be to use a 230V rotary phase converter and then step up from there with a 3 phase 460:230 VAC transformer wired backwards.

    One advantage of this is that most transformers have adjustable taps and this allows you to balance phases a little easier. And it seems these transformers are available as surplus for less cost. We have picked up 3 transformers like this ranging from 7.5kVA to 30kVA in the last 2 months from $100 - $200 each
    Where are you finding these transformers? Local?

  9. #9
    RPMWFO is offline Plastic
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    Quote Originally Posted by k3vyl View Post
    You could also use three 2.5 kva control transformers downstream of your converter.They are easier to handle and obtain.I know a fella that ran his 460V hardinge lathe off that setup.It may even be a good thing because of isolating the load from the neutral of the single phase supply.
    Would these be single phase transformers? What would the step up ratio have to be in this case? What is the best place to look for said transformer(s)?

    Sorry I am little weak electrically. It's been a long time since I had to know anything in depth about electrical theory.....

  10. #10
    Mike C. is online now Diamond
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    My suggsetion would be to build and run a 220 rotary phase converter and then run the output through a three phase stepup/stepdown transformer to get your 440. Reason? Now you have 220 three phase available, as well as 440.

    As for the transformer, there are usually a couple on Ebay al the time. You can check with local industrial electrical companies and surplus equipment dealers. Should be able to pick one up for $100-200. Most can be tapped for a wide range of voltages, so (of course) check the jumpers before hitting the juice.

  11. #11
    dep [INDY] is offline Aluminum
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    Quote Originally Posted by motion guru View Post
    Another option would be to use a 230V rotary phase converter and then step up from there with a 3 phase 460:230 VAC transformer wired backwards.

    One advantage of this is that most transformers have adjustable taps and this allows you to balance phases a little easier. And it seems these transformers are available as surplus for less cost. We have picked up 3 transformers like this ranging from 7.5kVA to 30kVA in the last 2 months from $100 - $200 each
    This thread is interesting. I have a Duke Energy (PSI) single phase 240v rural service, I get 240v 3-phase generated by an RPC, looking at an oven that requires 440v, 48.8 amps (has 1hp blower motor).

    Studying various catalogs I see some 3-phase transformers designed to produce 480v from 240v and others from 480v to 240v.

    Transformers are reversible . . so why are they cataloged separately?
    Thanks

  12. #12
    jackalope is offline Titanium
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    I have done just as has been mentioned here. I have 220v single phase power to my building. I also have a 3/5 dual hp rated WEG motor that is 440v. My rpc is a 30hp unit getting it''s juice from the supplied 220v single phase 50amp breaker. I bought a 30kva dry transformer and wired it backwards. Basically, I ran wire from the RPC, to the transformer, then to the lathe. All works just fine.

    It was mentioned here that having the various taps on the transformer allowed you to dial it in so as to allow all phases to be nearly equal. With my experience in doing this, when I hade them on different taps, it would blow the breaker in short order and the transformer made a loud buzzing/humming sound before tripping???? Not sure if that was just something with MY transformer or what?

  13. #13
    NewTown is offline Plastic
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    Transformers are reversible, however, there is some loss that is accounted for when used for the stated step up or down. When you reverse the transformer, that loss is still accounted for, only in reverse, so a 480V to 240V transformer when supplied with 240V may not give you the full 480V output.

    This thread is interesting. I have a Duke Energy (PSI) single phase 240v rural service, I get 240v 3-phase generated by an RPC, looking at an oven that requires 440v, 48.8 amps (has 1hp blower motor).
    That is an insane oven. You would need a huge RPC to handle 48.8amps @ 440V (Nearly 100amps 240V 3 phase supply which would require even more than that from single phase).

    It was mentioned here that having the various taps on the transformer allowed you to dial it in so as to allow all phases to be nearly equal. With my experience in doing this, when I hade them on different taps, it would blow the breaker in short order and the transformer made a loud buzzing/humming sound before tripping???? Not sure if that was just something with MY transformer or what?
    I haven't heard of doing this before. It was always my understanding that balancing the lines would require capacitors. You will get an unbalanced load on the transformer if you use multiple taps.

  14. #14
    motion guru's Avatar
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    sorry for the late reply - we found these transformers locally - one from a guy we bought a CNC turning center from (he had purchased several before changing plans on how he wanted to run power in his shop) The others were from local auctions we attended.

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