3 phase hoist on single phase

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

  1. mtma

    mtma Member

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    The way those links are oriented, looks like it's already in star?
     
  2. di_entropy

    di_entropy Member

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    That IS wired in Star.

    The bridging links on the left side is creating the Star point.

    I would rewire the motor terminals to Delta then get a 230V 1PH to 230V 3PH output VFD, get rid of the reversing contactors and just use the up/down controls to switch a relay for the forward/reverse input on the VFD.

    Can't quite tell how the brake is wired, looks like it may even be powered off a phase from the motor terminals? But I would rewire this so it is switched by an auxiliary contactor off the same start signal for the new VFD, with a separate 230V 1ph supply.
     
  3. mr camouflage

    mr camouflage Member

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    How much more expensive would getting 3 phase power installed cost?
     
  4. di_entropy

    di_entropy Member

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    It is a decent size motor (for domestic/commercial stuff) that is right on the limit for a single phase input VFD.

    For what I mentioned above I'd be guessing around $700 in materials plus a days labour.. $12-1500ish.

    Who knows what getting 3-phase would cost, depends on the building, existing switchboard, etc. Definitely more than that, but worth investigating.
     
  5. OP
    OP
    CacTuar

    CacTuar Member

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    Cheers, the issue is that there is one of these motors on each Pylon. So there's 2 of them that work together, so any vsd would have to do both sides at once. 2.6 * 2 = 5.2kW VSD.
    From a quick Google, that's pretty big.
    Edit: unless I get 2 of them, rated at => 2.6kw and somehow control them together? Is that possible?
     
    Last edited: Sep 25, 2020
  6. mtma

    mtma Member

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    Becoming sketchy here without an actual wiring diagram and associated information.

    The hoist will have some method of keeping itself in sync. Since there are two full sets of reversing contactors, it is possible that it has some kind of measurement or imbalance detection mechanism and it momentarily stops one side if it hasn't caught up with the other motor. Or maybe it stops totally and the operator has to level it manually. Otherwise there could be some mechanical synchronisation between the motors but it could be a 'soft' connection with that wiring setup. The mechanical connection if present might not be able to balance a shift in all situations. In this case you probably need to replace each set of reversing contactor with a VFD which responds to the original contactor signal from the control unit - possibly via relay as suggested if required - so the design functionality is preserved.

    Additionally you need to figure out how the brake works and make sure it does work after the retrofit.

    VFD's generally don't like contactors doing things on their motor-side terminals, it is a typical invitation for failure. When implementing such a system in most cases the VFD needs to come to a halt and disable before you can change the contactors, so in this case you shouldn't attempt to use a single VFD with downstream contactors as the controller will do its own thing. A VFD isn't a proper generator-inverter by itself.

    If this is one of those advanced hoist systems that have free flexible positioning it's probably best to investigate a manufacturer mod or sell it and get an appropriate hoist for the installation.
     
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  7. Symon

    Symon Castigat ridendo mores

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    Not a problem as long as your single phase motor has the same internal braking arrangement. If it doesn't then you need to have an external brake which is getting into territory you don't want to go down.

    It is possible, but not easy. If you are going to go the VFD route then get a single unit to power both motors at once.

    It would be wired off one phase to release the brake when the motor is powered. If he goes the VFD route then it would need a very short ramp up time to account for that. Getting a single phase motor would still be my preferred option.

    He's already addressed why that's not a good option for him.
     
    Last edited: Sep 25, 2020
  8. OP
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    CacTuar

    CacTuar Member

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    Yep I agree with you. I think this will be the simplest option, based on all the info that's been given above by yourself and others. If only I can find a suitable replacement motor. I will have to go back and take one of the motors off to get some photos of the way it's mounted to the hoist so I can get the same mounting on any new motor.
    This is a shot of the blue box if that helps. So it just puts a DC current over one of the windings to lock the motor in place when stationary?
     

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  9. Symon

    Symon Castigat ridendo mores

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    It would be a spring applied brake. When the motor is energised it also powers that bridge rectifier to put DC onto the brake solenoid to lift it. When the motor turns off so does the solenoid and the spring applies the brake.
     
  10. OP
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    CacTuar

    CacTuar Member

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    So I've spoken to few companies and they say a couple of different things. One offered single phase motors that could possibly replace the existing 3 phase ones, another company offered VFDs but upon closer inspection they were only available in 3 phase in the size I would need (as a single unit, not one for each motor). Another company said VFDs wouldn't be suitable anyway because they would cause chatter on the contactors, and offered a rotary converter instead. It would be around the $4k mark for one of those, which I could probably upgrade his house to 3 phase for that.
     
  11. Symon

    Symon Castigat ridendo mores

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    For that kind of coin you could replace the hoist with a single phase one.
     
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