Lathe motor faulty?

  1. hunter27

    hunter27 Pete

    Messages:
    492
    Location:
    Lancashire UK
    Sorry Following on from my VFD/potentiometer thread I'm beginning to wonder if it could be the motor at fault or both.
    I have been running a Boxford 3 phase lathe using a VFD on single phase for around 2 years now. The remote speed pot stopped working on my 20years +VFD and the lathe would only run at aprox 1/3rd speed.
    The very helpful chap at IMO inverters suggested I check the motor which I did as best as I could,it's 3 phase in delta I disconnected all the wires and identified the phase loops, they all gave the same resistance reading, I checked every phase to earth with a multimeter and between the phases and it all seemed to check out okay.
    I then tried my sons Chinese VFD on it and although the speed picked up a little it's still nowhere near what it was or should be, also if I set the pulleys to the fastest setting the lathe will not start as the motor just buzzes. There is no great resistance turning the chuck by hand.
    I don't thing I should be able to stop a 4"chuck running at around 700RPM using just my hands on a 3/4HP motor. That was on the second fastest pulley options.
    I don't want to replace the wrong bit what do you think?
    Pete
     
  2. eLuSiVeMiTe

    eLuSiVeMiTe Forum Supporter

    Messages:
    9,936
    Location:
    Bedfordshire England
    Try another motor on the original vfd if all works as intended its a good indication
     
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  3. daleyd

    daleyd Member

    Messages:
    6,155
    Location:
    Wrexham, North Wales
    Was your lads vfd set up for another motor? Does it have some auto tune function (where it measures the winding resistances etc and calculates some parameters) and has it been set up to correctly reflect your motor that’s now fitted to it? There will be parameters for things like max/min speeds, max current, number of poles etc - if these are incorrect then it won’t perform right.
     
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  4. hunter27

    hunter27 Pete

    Messages:
    492
    Location:
    Lancashire UK
    Thanks both

    eLuSiVeMiTe I'm hoping to try my inverter on sons 3phase Harrison lathe tomorrow.

    daleyd We set it up as best we could for my motor using a set of instructions off the internet for a unit that looked almost the same :( but no autotune as I could see.

    I know there are also frictional forces and gearing involved but do you think I should be able to stop a 3/4hp motor by hand?
    Pete
     
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  5. daleyd

    daleyd Member

    Messages:
    6,155
    Location:
    Wrexham, North Wales
    Not if it’s set up right Pete, but I have a Siemens inverter on mine and when I first fitted it I could do similar, until I did an auto tune. Mine is an American spec motor so is a bit weird compared to a standard European spec one, but it didn’t matter what settings I used it wouldn’t run right until I did this.

    I don’t know if your inverter or motor is the same but it sounds like something is not quite right - the config is something worth checking out first though as it’s possible it could be incorrect and should be able to be changed, it’d be a shame to change the motor or inverter if it’s not needed. As @eLuSiVeMiTe says above it might well be worth trying another motor as well.
     
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  6. hunter27

    hunter27 Pete

    Messages:
    492
    Location:
    Lancashire UK
    The chap at IMO inverters asked for details of my old Crompton motor and said the default settings should be fine for it. I have not changed anything on my lathe set-up since I got it, the motors data plate only mentions volts star 380/440 and amps star 1.5 no mention of delta which I think I need for this set up. The wiring on my motor is like this and are no links and only 3 posts but I think it is delta.
    motor wiring.jpg
     
  7. Pete.

    Pete. Member

    Messages:
    8,655
    Location:
    Kent, UK
    Since the windings check out on a meter I find it very hard to believe that it's at fault. A 20yr old VFD I would be very suspicious of.
     
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