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3 phase hoist on single phase

Discussion in 'Electronics & Electrics' started by CacTuar, Sep 24, 2020.

  1. CacTuar

    CacTuar Member

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    So I'm an electrician but I did the AC machines modules 16 years ago and I very rarely deal in industrial electrical work.

    A client has a car hoist with 2 x 2.6kW 3 phase motors on it. They are currently wired in delta. The controller seems to just be two sets of 4 pole contactors that are interlocked and just swap one of the phases so that the motors run one way or the other, depending on if you want the hoist to up or down.

    He only has single phase available on site.

    What's the best way to leave him with a functional hoist? Change the 3 phase motors to single phase ones? Get a 1 phase to 3 phase changer?

    If you recommend changing to single phase motors, any suppliers you know of that could help would be greatly appreciated.

    Thanks in advance
     
  2. Fred Nurk

    Fred Nurk Member

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    Reversing single phase motors is either a pain in the arse, or not possible, depending on the specifics of the motor.
    VSDs can do the single / 3 phase conversion, but there's a number of catches, including the need to oversize the drive by at least 100% to compensate, and ensure that the motor is the correct voltage to get away with it (VSDs are all sorts of magic, but they don't create 415V from 240, the best you'll get is 3 phase 240...)

    There likely isn't an easy or cheap solution here.
     
  3. OP
    OP
    CacTuar

    CacTuar Member

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    Thanks for the reply. If I was to use a VSD and wire the motors in star, would that work? I know the thing would be slower, but would it be an option?
    And yeah, not expecting any option to be cheap :wired::sick:
     
  4. JSmithDTV

    JSmithDTV Member

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  5. heller44

    heller44 Member

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    Remember that star connected motors are ~1/3 the torque of delta connected. Not what I'd recommend for a hoist.

    See if the manufacturer sells the same or similar unit in single phase. Then buy what they use.
     
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  6. Symon

    Symon Castigat ridendo mores

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    Post up a photo of the nameplate, the main thing I am looking for is the frame size.

    You have the following options -

    1. change with single phase motors and modify the controls to do the reversing. This is pretty simple.
    2. use a VSD. These are pretty cheap now and plenty will do the boost conversion to give you 400V. This is probably your simplest option.
    3. do the single-phase to three-phase trick with a few capacitors. I don't recommend this unless you know what you are doing.

    For something like a hoist you are looking at very intermittent duty, and he will be running the motor at its rated speed, so cooling shouldn't be too much of an issue.
     
  7. heller44

    heller44 Member

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    Symon, got a link to a vsd with voltage step up?
     
  8. Symon

    Symon Castigat ridendo mores

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  9. OP
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    CacTuar

    CacTuar Member

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    As requested- thought I may as well post the insides of the controller as well.
    1. I originally thought whacking single phase motors over the interlocked contactors to reverse would work. Contactors and control wiring I can do.
    2. the VSD would have to handle the FLC of both motors = 2.6kW x 2. Should it be sized to factor in the startup current though?
    3. I don't know what I'm doing with motors, so this probably isn't the option for me.

    EDIT: Did you mean plate off the hoist or off the motor?
     

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    Last edited: Sep 24, 2020
  10. ShadowBurger

    ShadowBurger Member

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    Hoists are so common on the second hand market I can't fathom spending more than a few thousand to get one up and running when the option of simply selling it and getting one suitable isn't that difficult.

    Yep you can use a 1-phase to 3-phase converter, note that the current draw at 240v will be substantially higher due to the voltage conversion and losses due to inefficiency. An 8kW unit will want 40A so you're looking at electrical work to set it up: https://www.tortech.com.au/product/...-three-phase/single-to-three-phase-converter/

    Why doesn't he put 3 phase in? I've been quoted $2,800 for having it connected to my garage (underground power, cheaper if he has above ground).

    Other than that, +1 the idea of just buying a 3 phase generator - under $3k will get a 6kW just from cursory googling.

    But again if this is a home garage setup, getting a suitable hoist is really the right decision.

    EDIT: the key bit of info is; what is his budget for getting it set up
     
    Last edited: Sep 24, 2020
  11. ShadowBurger

    ShadowBurger Member

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  12. heller44

    heller44 Member

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    Interesting. I gather it would be some sort of dc doubler, electrically noisy as hell, maybe why only china makes them from what I can see so far.

    Agree with all this.

    Also if you modify a hoist, and worksafe or whatever is in your state have reason to come and check it, you might have issues. They are hot on hoists over here.
     
  13. OP
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    CacTuar

    CacTuar Member

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    I'm an electrician so I can arrange to get 3 phase connected, but it would be a prick of a job here with undergrounds and the general weeks of truck appointments and switchboard rewiring etc. I'm hoping there's another option but it would be my last resort if needs be.
     
  14. ShadowBurger

    ShadowBurger Member

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    Inverter based, so just FET generated output trying to emulate the triple sine. Yeah it would be noisy as hell at that price point, but a high end one could easily produce a cleaner signal than mains
     
  15. ShadowBurger

    ShadowBurger Member

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    If it's just for the hoist, does he really need his switchboard rewired? If that's the main problem, leave the existing wiring as is and put in a standalone breaker / mains switch to wire in the hoist. Assuming that's possible within the bounds of the rules.
     
    Last edited: Sep 24, 2020
  16. Symon

    Symon Castigat ridendo mores

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    It's a 100L frame size, common as. The only issue is it looks to have an internal brake. I'd get on the phone to the usual suspects - WEG, TECO, etc and see if they make a single phase equivalent.

    Just a boost converter prior to the DC bus, and then the rest of the drive is as per normal. They've been around for some time, it was at least 10 years ago when I recall seeing sales reps talking them up.
     
  17. heller44

    heller44 Member

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    Not the output, the voltage doubler internally would generate heaps of EMI. With enough filtering on the output and input you might not see too much, but there is no way they are building that in to a drive at that price point.
     
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  18. OP
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    CacTuar

    CacTuar Member

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    You have to rewire the switchboard(s) when you upgrade. The main switch now requires 3 poles instead of one plus the new 3 pole circuit breaker that protects the submains to the shed, and this board doesn't have any more room already. You have to balance the circuits over the three phases. All stuff I would rather not do, especially if it means I could do something different that I haven't done before, even if it's just a motor change over.

    Thanks. I did see the brake mentioned on the junction box on the motor. Would that be a problem when changing to a single phase equivalent?
     
  19. di_entropy

    di_entropy Member

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    Do you have electrical drawings for the hoist, and what does the actual nameplate on the hoist say?

    Strange that the motor is wired in Delta, the motor nameplate shows that they are a 230V Delta motor and it is 415V for Star.

    This makes me think the hoist may be already designed for 230V single phase input and have some sort of converter to output 230V 3-phase?

    Otherwise the easy solution is just to use a single phase VFD or variable frequency drive, this will take 230V single phase input and give you 230V 3-phase output which is what your motor is wired for.

    If you do this you will need to be mindful of what is switching the brake.
     
    Last edited: Sep 24, 2020
  20. OP
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    CacTuar

    CacTuar Member

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    This photo I forgot to upload before- it just show the junction box inside but this is how it's wired. To change to star I would move the links over to the corresponding terminals.
    The plate on the hoist definitely says 400v/50hz 3 phase. It came out of a mechanics that went under and hasn't been touched since it got into it's new home.
     

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