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  1. #1
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    Default 3 Phase Generator Motor Powered by Single Phase Motor?

    Hey Guys, is it as easy as running a 3 phase motor as a generator powered by a single phase motor to run 3 phase power out in the shed?

    are there any complications? i have been looking online at making one but thought i should ask first

    looking to power 3 phase lathes and older mode 3 phase welders and tools

    https://www.youtube.com/watch?v=FeH580M336c

  2. #2
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    Sadly not as easy as that..... 3-phase alternators have a field winding which is controlled, motors have just a soft iron core.
    As you can imagine, if it was as easy as that, eveyone would be doing it.
    The solution is either a rotary phase converter (expensive, noisy and inefficient) or a VFD (relatively cheap, very efficient and lots of benefits like gentle acceleration, variable speed, active braking and motor protection).
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  3. #3
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    I'm not sure what u mean mate? I'm going by this link http://www.redrok.com/cimtext.pdf everyone is doing it on Youtube just i have not seen any MIG welders using it only ARC

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    I didn't bother to read all of that doc, but I suspect that it may just be using the 3 phase motor as a phase converter, being helped along by a single phase motor ... but I could be wrong.

    Phase converters need not be expensive or noisy, but I'm not sure about how inefficient they are.
    I have 5x3 phase machines and having a VFD for each one would cost a small fortune. My phase converter cost me about $150 (used a lot of scrounged parts).
    Cheers.

    Vernon.
    __________________________________________________
    Bite off more than you can chew and then chew like crazy.

  5. #5
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    PS : You also can run into issues with VFD's if the machine has multiple 3 phase motors in it.
    Cheers.

    Vernon.
    __________________________________________________
    Bite off more than you can chew and then chew like crazy.

  6. #6
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    Quote Originally Posted by Vernonv View Post
    I didn't bother to read all of that doc, but I suspect that it may just be using the 3 phase motor as a phase converter, being helped along by a single phase motor ... but I could be wrong.

    Phase converters need not be expensive or noisy, but I'm not sure about how inefficient they are.
    I have 5x3 phase machines and having a VFD for each one would cost a small fortune. My phase converter cost me about $150 (used a lot of scrounged parts).
    Vern do u have any pictures of a phase converter?

    I'm always on a tight budget for tooling so i see all these great older model machines going for next to nothing because they are 3 phase, 3 phase is not available to me its a shame i would have had it installed years ago and the price of the older machinery to the Chinese tools these days is about equal but i think the older used gear is far superior in quality like the older CIGWeld or WIA welders go for nothing these days

    i will have to do some research on the phase converter, so far i have only came across two types of generators one was as mentioned a small electric 240v motor powering a 3 phase induction motor to create 3 phase power (i was looking to make around a 7.5-10kw model) and another one was using just a single 3 phase motor on its own with capacitors (i'm unsure how this one works)

  7. #7
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    Joe's information is correct, it's not as easy as that. I read your PDF link and yes they make it sound easy BUT:

    They are dealing with 60Hz 110V mains, not our 50Hz 230V mains. (Concepts should hold but values etc would change)
    The values of the capacitors used vary with load, and aren't specified at at any power level, it always has been a suck and see style arrangement match caps to the load.
    A normal alternator has two groups of windings, one fixed and one rotating. A controlled current passes through one winding and the shaft is rotated at a fixed speed to generate the output frequency required. (50Hz in our case). The controlled current is used to control the output voltage. Three phase units being powered by the device require reasonably accurate control of frequency and voltage, although some latitude is permissible if you do not need accurate speed and power from the unit being driven.
    As described in the article you linked to, the output voltage is being controlled by the drive RPM of the alternator, which means that the output frequency will vary with the output voltage, not good for operating motors or medium sized transformers in old style welders etc, as either the machine speed or transformer output voltages and frequencies become uncontrolled, or you risk operating the unit at voltages exceeding their input specifications and risk premature failure. There does not seem to be any mention of what they are trying to drive in the article, other than using a lightbulb as a test device. The system as outlined is viable if you want to drive something like strings of bulbs, or heating elements, which are voltage sensitive but not frequency sensitive.

    A rotary phase converter uses the 3 phase motor with one phase winding connected to mains power, and capacitors and the two remaining phase windings being used to synthesize the other two phases, but again the capacitor values need to match the load applied, and vary significantly. There is a computerized unit sometimes advertised on ebay that can switch various capacitors in and out of circuit to try and match the capacitors to the load, avoiding the need for the operator to monitor and manually switch capacitors to match the load, but it isn't cheap.

    Regardless, if you want to be able to "make" 10KW of three phase power, you need at least 10KW of single phase to start with, more likely 13-15KW when you take mismatching and inefficiency into account. At 230V, thats in the order of 60 to 65A. Oh, and you would only be generating a nominal230V phase to phase so all of the units you drive this way would need to be able to be configurable for delta connection, just as if you used a VFD unit to generate the three phases.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  8. #8
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    Quote Originally Posted by malb View Post
    Joe's information is correct, it's not as easy as that. I read your PDF link and yes they make it sound easy BUT:

    They are dealing with 60Hz 110V mains, not our 50Hz 230V mains. (Concepts should hold but values etc would change)
    The values of the capacitors used vary with load, and aren't specified at at any power level, it always has been a suck and see style arrangement match caps to the load.
    A normal alternator has two groups of windings, one fixed and one rotating. A controlled current passes through one winding and the shaft is rotated at a fixed speed to generate the output frequency required. (50Hz in our case). The controlled current is used to control the output voltage. Three phase units being powered by the device require reasonably accurate control of frequency and voltage, although some latitude is permissible if you do not need accurate speed and power from the unit being driven.
    As described in the article you linked to, the output voltage is being controlled by the drive RPM of the alternator, which means that the output frequency will vary with the output voltage, not good for operating motors or medium sized transformers in old style welders etc, as either the machine speed or transformer output voltages and frequencies become uncontrolled, or you risk operating the unit at voltages exceeding their input specifications and risk premature failure. There does not seem to be any mention of what they are trying to drive in the article, other than using a lightbulb as a test device. The system as outlined is viable if you want to drive something like strings of bulbs, or heating elements, which are voltage sensitive but not frequency sensitive.

    A rotary phase converter uses the 3 phase motor with one phase winding connected to mains power, and capacitors and the two remaining phase windings being used to synthesize the other two phases, but again the capacitor values need to match the load applied, and vary significantly. There is a computerized unit sometimes advertised on ebay that can switch various capacitors in and out of circuit to try and match the capacitors to the load, avoiding the need for the operator to monitor and manually switch capacitors to match the load, but it isn't cheap.

    Regardless, if you want to be able to "make" 10KW of three phase power, you need at least 10KW of single phase to start with, more likely 13-15KW when you take mismatching and inefficiency into account. At 230V, thats in the order of 60 to 65A. Oh, and you would only be generating a nominal230V phase to phase so all of the units you drive this way would need to be able to be configurable for delta connection, just as if you used a VFD unit to generate the three phases.
    Thanks for the post Malb Do u know if there is a DIY 3 phase voltage regulator i can build or possibly buy one? i will do some searching now

    i had rushed out and bought the only decent HP motor i could find than came home and seen your reply but none the less i will still go a head with plan A and build a 3 phase generator i will sort thru the problems if possible

    the motor is a 13.7amp, 415v, 3 phase motor i think it works out at 10hp i can purchase one of those Honda knock off motors from Ebay to run this motor, only down side i think will be noise because it requires 2900RPM running speed but if i can pull this off and have a stable voltage supply it should work ok

    one other weird thing i noticed is there are two cut wires that go into the electrical box, one wire is 1 phase the second is 3 phase the motor states 3 phase on the builders plate so why would 1 phase be wired up?
    Attached Images Attached Images

  9. #9
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    Why not get genuine 3-phase power brought into your house? Excuse is 'I have 3-phase machinery'.

    Cheers
    Roger

  10. #10
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    The single phase cable is probably to have a 415V worklight or a transformer connected and the 3-phase cable to run the motor.
    Note that your motor is a DELTA wound motor for 415V 3-phase. NOT 'star' wound as in the linked pdf file. You will need to do some more reading about capacitor selections to try what you want to do in plan B (rotary converter).
    But I would suggest that you just try plan A first and report how you go. Nothing is learnt by not trying things others have dismissed
    You can't do much harm and you will only waste a litte time (if you already have a suitable drive motor, or buy one you can use for something else down the track). You never know, all those Youtube types might be right after all (and all the electrical engineers wrong).
    The only thing you shouldn't do here is NOT reporting successes or failures. We all support each other and are glad to learn from each other!
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  11. #11
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    if you want to be able to "make" 10KW of three phase power, you need at least 10KW of single phase to start with, more likely 13-15KW when you take mismatching and inefficiency into account. At 230V, thats in the order of 60 to 65A.

    Good luck trying to pull that out of a domestic single phase supply. I can see fun and games with the main switch board fuses for a start. And then with the fire brigade, electricity supplier inspector, and your insurance company. You may invalidate your insurance policy along the way.

    Comment: this is NOT a game for amateurs.

    Cheers
    Roger

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    Quote Originally Posted by gazza2009au View Post
    Vern do u have any pictures of a phase converter?
    There are plenty of examples on the web ... or did you specifically want a pic of mine?

    BTW you can also convert some of the older transformer based mig welders from 3 phase to single phase ... I've got an old UniMIG 350 that I converted. I thought I had posted the conversion here, but I can't seem to find it now ... I'll keep looking.

    EDIT : Here it is
    Cheers.

    Vernon.
    __________________________________________________
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  13. #13
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Vernonv View Post
    There are plenty of examples on the web ... or did you specifically want a pic of mine?

    BTW you can also convert some of the older transformer based mig welders from 3 phase to single phase ... I've got an old UniMIG 350 that I converted. I thought I had posted the conversion here, but I can't seem to find it now ... I'll keep looking.

    EDIT : Here it is
    We've had "donations" of several of these converted welders at the mens shed.
    A small one had a 15A plug and drawing about 12A max was OK on a 15A circuit.
    A much bigger one came in with a "somewhat scorched" 10A plug and was trying to draw over 20A!

  14. #14
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    Quote Originally Posted by jhovel View Post
    The single phase cable is probably to have a 415V worklight or a transformer connected and the 3-phase cable to run the motor.
    Note that your motor is a DELTA wound motor for 415V 3-phase. NOT 'star' wound as in the linked pdf file. You will need to do some more reading about capacitor selections to try what you want to do in plan B (rotary converter).
    But I would suggest that you just try plan A first and report how you go. Nothing is learnt by not trying things others have dismissed
    You can't do much harm and you will only waste a litte time (if you already have a suitable drive motor, or buy one you can use for something else down the track). You never know, all those Youtube types might be right after all (and all the electrical engineers wrong).
    The only thing you shouldn't do here is NOT reporting successes or failures. We all support each other and are glad to learn from each other!
    Awesome mate, in that link i posted they said if i over loaded the generator it would just stop working but I'm not sure about the capacitors and if i did go over voltage and by how much and what max voltage capacitors i use if it would effect them... so some reading needed

    I'm very keen to try it

  15. #15
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    Quote Originally Posted by Vernonv View Post
    There are plenty of examples on the web ... or did you specifically want a pic of mine?

    BTW you can also convert some of the older transformer based mig welders from 3 phase to single phase ... I've got an old UniMIG 350 that I converted. I thought I had posted the conversion here, but I can't seem to find it now ... I'll keep looking.

    EDIT : Here it is
    Sorry Vern miss read what u said i thought u had turned single phase into 3 phase thru a converter

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