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  1. #1
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    Default Replacing A Single Phase Motor With A Three Phase Motor....................

    Yes you read that correctly, I want to replace the 2hp 1ph motor on my lathe for a 5hp 3ph.
    So my questions are;

    # Physical motor size, Will there be much of a difference in the diameter of the motor ?

    # Control box, With the cover off the back of the lathe's electrical switch board all I can see is 50 - 60 relays and micro switches etc, etc. So I need to know if these can somehow be used on 3ph power somehow. Maybe by only using 1 leg of the 3ph ?

    # I suppose I should add there will also be the switches etc etc, I'm still wondering like above if they can also be made to work off 1 legh of the 3ph ?

    Obviously there are many other questions running around in my head, But this is a start to see what others here in our forum family think would be a good way to go about it.

    Extra points possibly worth a mention are,

    Lathe is an AL340
    The power is true 3ph off the grid, So no converters or vfd required,

    Well thats it for now, Heres hoping we can all group together and get this solved.

    Thanks in advance
    Matt
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  2. #2
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    Off the top of my head - lots of pain coming up.

    Looking through a Brook-Crompton catalogue for comparative sizes, a 2HP 2 pole (single phase) motor has a 5/8" shaft, is 290mm long and 178mm in diameter. By comparison, a 5HP (3 phase) motor at the same speed is 322mm long, 215mm diameter and has a 28mm shaft.
    3 phase motors will run on 2 phases (badly perhaps, but they will still run), so control of them will need to be done using contactors. You might be able to pick some up on Ebay, but they are not cheap when bought retail.
    Finally, the obvious statement - that is a fair increase in power. Is the lathe built for it? For the money, time and mucking around you may be better off finding a second hand industrial machine - native 3 phase, probably more rigid and better able to deal with the power. 5HP sounds a lot too - my lathe is only 3HP and is 28" between centres and has a 12" swing. Your AL340 probably is worth more as a single phase unit than a conversion to 3 phase too.

    Michael
    Last edited by Michael G; 26th Apr 2015 at 08:13 AM. Reason: spelling!

  3. #3
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    Probably need at least four or five relays, need to switch every phase. You will need relay for coolant, one for forward one for reverse, one master relay and probably another one here and there...

    Need a transformer to get 24V to power the relays, unless you want to run 415V all through all the micro switches in the machine..

    Need a new pulley.

    it is possible to do..
    Gold, the colour of choice for the discerning person.

  4. #4
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    > Yes you read that correctly, I want to replace the 2hp 1ph motor on my lathe for a 5hp 3ph.

    But you do not tell us, WHY you want to do that.

    - If it was because you want VFD variable speed and at the same time do away with a gerbox (be it a belt or metal gears), then yes it could make lots of sense to go for a bigger motor

    - If you just wanted VFD variable speed, then a 1.5 to 2HP motor would do perfectly well

    - if you just wanted a 3 phase motor without a VFD, just because it vibrates less and makes for better surface finish, and it can be plug reversed, then a 2HP motor is all you need

    - or has maybe the 1ph motor broken down, and you just want to switch to a 3ph replacement to leave future options for VFD open....

    So, without you telling us why the swith to 3 phase, its hard to help.




    # Physical motor size, Will there be much of a difference in the diameter of the motor ?

    Yes, a motor of same pole count will be considerably larger, one to two frame sizes larger.



    # Control box, With the cover off the back of the lathe's electrical switch board all I can see is 50 - 60 relays and micro switches etc, etc. So I need to know if these can somehow be used on 3ph power somehow. Maybe by only using 1 leg of the 3ph ?

    You will be able to hook up the control circuitry between one phase (one of the 3 phases) and Neutral. That is 240V, just like it was before. And many of the relay probably work on 24V via a step down transformer. However, if you are not experienced in electrics its probably not the ideal project to start learning.

  5. #5
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    Quote Originally Posted by cba_melbourne View Post
    You will be able to hook up the control circuitry between one phase (one of the 3 phases) and Neutral. That is 240V, just like it was before. And many of the relay probably work on 24V via a step down transformer.
    To amplify on Chris's answer, neutral to phase will provide 240V which will be the same as what you have so if there are 240V contactors for a coolant pump for example, you can still use that bit. However, you will not be able to control a 3 phase motor by switching just one phase with a 240V single phase contactor.

    Michael

  6. #6
    BobL is offline Member: Blue and white apron brigade
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    Most larger three phase motors on machine will have some sort of thermal overload protection switch and a no-volt de-latching switch which trips out if the power fails or the thermal overload switch cuts in. I understand some folks don'e worry about these but I guess it depends how much you value your gear? The reason I'm bringing this up is that unless you can find some used switch gear, the cost of new switch gear could approach the cost of a VFD which if correctly speced an programmed provides similar functions and a whole lot more.

  7. #7
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    Hi Mathew,I have done a few single to 3 phase VFD conversions. Won't make comment on the how to etc. but wrt to contractors, there are many 3 phase contactors on ebay for under $20 delivered. You just need to work out what you want switching them, whether it be 415V, 240V 24V or 12V. 24V seems to be the most common. Most of these contactors have 3 poles (for switching the 3 phase) and an extra NO or NC which you can use to make them latching etc or use for other switching mechanism. When I design and wire up a conversion (surface grinder being my last) I always make them latching so that if power is lost etc. it will never come on unexpectadly when power is returned. Also makes an emergency stop very easy as all you have to do is cut the 24V supply. Oh, I never have 240V etc going to switches either so never use contactors powered by anything but 12 or 24V.Cheers & good luck!Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  8. #8
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    Hi gents,
    And thankyou all for taking the time to reply with your advice.
    My reasons for wanting to do the conversion are quite simple really.
    The 2hp motor that is on the lathe has been nothing but trouble from the
    day I brought the lathe home. I have replaced both caps at least 3 times each in 3 1/2 years,
    and after the first 6 months of use I really felt the motor had lost it's oomph.... In
    use it feels like it's only a 1hp motor. If I take any more than 0.5mm cut it bogs down, pulsates and
    struggles to cut.
    So I thought upgrading to a larger 3ph motor would be the best option. But after reading the comments so far
    maybe buying a quality 3hp single phase motor would be a better solution.

    I had no intentions on ever running it on a VFD, I just figured 3ph would be a smoother running motor.

    Thanks again for your help guys.

    Matt
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  9. #9
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    Quote Originally Posted by matthew_g View Post
    Hi gents,
    And thankyou all for taking the time to reply with your advice.
    My reasons for wanting to do the conversion are quite simple really.
    The 2hp motor that is on the lathe has been nothing but trouble from the
    day I brought the lathe home. I have replaced both caps at least 3 times each in 3 1/2 years,
    and after the first 6 months of use I really felt the motor had lost it's oomph.... In
    use it feels like it's only a 1hp motor. If I take any more than 0.5mm cut it bogs down, pulsates and
    struggles to cut.
    So I thought upgrading to a larger 3ph motor would be the best option. But after reading the comments so far
    maybe buying a quality 3hp single phase motor would be a better solution.

    I had no intentions on ever running it on a VFD, I just figured 3ph would be a smoother running motor.

    Thanks again for your help guys.

    Matt
    You know, reading through your post, it sounds like your motor is suffering from bad connections, particularly when you say "after the first 6 months of use I really felt the motor had lost it's oomph" and capacitor replacement. Before spending any money I would have a very close inspection of the wiring, particularly around the motor itself. You might just find that a bad crimp joint or a loose terminal is the root cause of the loss of oomph.
    Best Regards:
    Baron J.

  10. #10
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    Hi Matthew,
    Looking at my lathe, other than adding a thermal overload as BobL mentioned, very little would need to be changed, though there would be a small amount of rewiring. The contactors are 3+ pole (I assume 415V rated, there is a label over the rating). If your lathe is the same all the control/light/pump wiring can "likely" stay unchanged, just the mains supply to the contactors and from contactors to motor needs to be changed. Of course your lathe wiring maybe nothing like mine.
    What others have said still applies though 5hp is a lot more. Why not a 2hp motor? you have a 5hp already?

    Stuart

    p.s. if yo were to change 2hp to 5hp the contactors may not be rated for the current required. But as you've double the V and gone to 3 phase I wouldn't know off the top of my head.
    Last edited by Stustoys; 28th Apr 2015 at 02:44 PM. Reason: p.s.

  11. #11
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    if yo were to change 2hp to 5hp the contactors may not be rated for the current required. But as you've double the V and gone to 3 phase I wouldn't know off the top of my head.
    Unless you are planning to scale up the size of work you do and start taking thick cuts from a large billets the 5HP motor is not going to be pulling any more current than a 2HP anyway.

  12. #12
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    G'day Matt,
    A 3 phase motor is more efficient than a single phase motor so more power actually reaches the shaft meaning you could probably replace your 2hp 1~ motor with a 1.5hp 3~ and not notice the difference.
    Using a 2hp or 2.5hp 3~ Should give you a nice upgrade but I wouldn't risk going any higher than that. I'm not familiar with your particular lathe but usually the internal mechanical elements of a machine are dimensioned for a given input power rating and hooking up an oversized power plant may well result in excessive strain and premature failure. Think connecting a V8 to a ride on mower power train.

    With regards to your switching elements, again I'm not familiar with your particular setup but I would think you should only need to replace the main motor contractor. Just check the control voltage of the existing main motor contractor and buy an equivalent 3~ unit. If you use a five wire mains connection you will be able to keep your 1~ contractors for things like lights and a 1~ coolant pump etc.

    Of course as mentioned, you could always buy another lathe that's already 3~, there's a nice looking Graz SAG 180 in Dandenong on gumtree
    Cheers,
    Greg.

  13. #13
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    Quote Originally Posted by kwijibo99 View Post
    A 3 phase motor is more efficient than a single phase motor so more power actually reaches the shaft.
    But, motors are rated on output, not input. 2hp is 2hp(well it should be)

    Stuart

  14. #14
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    But, motors are rated on output, not input. 2hp is 2hp(well it should be)

    Stuart
    Yep, 3P motors may be smoother but 2Hp on a dyno is 2HP whether its a real horse, a steam engine or a 3P motor

  15. #15
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