Help needed with lathe electrical’s!!

  1. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    I think Pete has it. There is 3 core wire coming out of what appears to be sealed brake unit on the end of the motor.

    The wires are coloured earth, blue and brown. They you one to each of the motor terminals.

    I think until I get a chance to test the brake itself I’m at a bit of a standstill!
     
    Memmeddu likes this.
  2. brightspark

    brightspark Member

    Messages:
    31,770
    Location:
    yarm stockton on tees
    well check it because its only 2 core and an earth if its a magnetic brake it only uses 2 core over 2 phases it wont need 3 wire
     
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  3. Memmeddu

    Memmeddu Member

    Messages:
    2,956
    Location:
    Italia Sardegna
    Or It might even be a single phase unit
     
  4. Malky Member

    Messages:
    147
    Location:
    Scotland
    I’m no sparky but have had many headaches with electric motors on augers driers etc. the guys above are a great help but what you originally described sounds like a 3phase motor trying to spin on 2phases (or even1), if it worked 3weeks ago you’re need to go back and look at what you have done differently, don’t think brake will be jammed but may not be energised.
    Going back to the lathe i have a similar but earlier machine, didn’t know it had a brake on the motor, the Chuck can be rotated whether it’s plugged in and powered up or not if that’s where you think the brake is.
     
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  5. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    So,

    ive pulled the brake off, it’s an electromagnet type. It does not however appear the be the problem.

    with it off the motor spins freely and smoothly. Bearings are good, no play on the shaft.

    however when the lathe is started the motor makes a fraction of a turn then stops and sits there humming.

    I bypassed the controls on the lathe and wire the 3 poles to the phase converter.
    It does the same thing. However if I hold the starter for the phase converter down the motor spins up and runs as one would expect. But as soon as the starter is released the motor on the lathe stops spinning and goes back to humming.

    the motor also gets warm in a short space of time.
    Is it knackered, and other potential testing I can do to confirm either way?
     
  6. Pete.

    Pete. Member

    Messages:
    9,819
    Location:
    Kent, UK
    If you weren't using a site transformer to provide 110v for the control side I would say that you have the control gear wired to the wild leg of the rotary converter.

    It does sound like you have a voltage problem. Perhaps some feature of the S&B motor requires more balancing of the phases, or perhaps it's pure co-incidence that you've had a capacitor go bad.

    Have you tried running another machine from the rotary since this problem began? If you have and if it was fine, I would look at wiring the motor directly to the lead and plugging it into the converter see what happens.
     
    hermetic likes this.
  7. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    Pete,

    yes, tried the phase converter on the mill and it has no issues starting it.

    I have wired the lathe motor direct to the phase converter. It behaves as explained above.... no different. It even bogs down the Idler on the phase converter when I start the phase converter. If I keep the starter for the phase converter held down the lathe motor spins up to speed. But as soon as the starter for the phase converter is released it stalls and the idler on the phase converter bogs down.

    testing the voltages on the phase converter gives the artificial leg at 416v and the other 2 at 450ish, can’t remember exact figures.
     
    Memmeddu likes this.
  8. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    Just double checked another machine on the phase converter, just to be sure! And it’s working just as it should!
     
  9. Pete.

    Pete. Member

    Messages:
    9,819
    Location:
    Kent, UK
    Sounds like the motor is duff then. What's it's rating?
     
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  10. Memmeddu

    Memmeddu Member

    Messages:
    2,956
    Location:
    Italia Sardegna
    I think to remember 3HP
    I would replace it
     
  11. WorkshopChris

    WorkshopChris Forum Supporter

    Messages:
    5,051
    Location:
    South East Essex
    Can you disconnect the motor from the mains and measure the winding resistances with a mltimeter and to earth. winding should all be the same or almost.
     
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  12. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    Hi Chris,

    I have done that, I can’t remember the figures now but they were all pretty much the same. And the terminals to earth gave nothing.

    I have discovered that if The headstock is in neutral the motor will spin up but very soon, like 10 seconds the thermal cut out kicks in. Even set to the max of 6 amps it still cuts out inside 15 seconds.

    Is it possible that the motor or the controls are not compatible with the phase converter? I don’t know if this is even possible.
     
  13. brightspark

    brightspark Member

    Messages:
    31,770
    Location:
    yarm stockton on tees
    have you disconnected the motor and put a direct feed to it from converter
     
  14. daedalusminos Member

    Messages:
    1,076
    Location:
    Norwich
    What was the previous owner using to power the lathe.....and have you got a photo of the motor data plate?
     
  15. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    It was powered from a rotary phase converter.

    I can’t find the name plate. It appears to either be where it can’t be seen or it’s gone.

    yes Brightspark I have. It behaves the same. As I’ve written in the posts above.
     
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  16. Memmeddu

    Memmeddu Member

    Messages:
    2,956
    Location:
    Italia Sardegna
    It should be fine noo exactly really good but fine .
    I have had to rebuild an electric motor
    And the windings are are around 3 ohms ∆
    7 ohms Y
    I've probably understand what is your problem .
    You said that
    Across two phases you read roughly 7 ohms right?
    But on the third you read less than 3 ohms
    So from what I can understand here we have our a short out winding.
    Or a wrong connection .
    Why?
    Because 3 ohms should be the resistance of the single winding
    What does means ?
    You are feeding current through the star point .

    Connect the phases where you read around 7 ohms
    The connection where you read less than 3 ohms is your star point .
     
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  17. Pete.

    Pete. Member

    Messages:
    9,819
    Location:
    Kent, UK
    Umm, I dunno how I missed this. You'll have to expand on what you were testing. There are two basic tests, both to be done with the supply wires removed from the motor.

    Phase-to-phase resistance check.
    Phase to casing insulation test.

    The most basic thing to do is un-wire the motor terminals and check the resistance between phases 1-2, 2-3, 1-3. They should all be the same or very close. If there's an internal short in a phase then 2 of them will be lower than the third. If there's a short to the casing then one might be low.

    If your check has been made phase-to-phase with those readings you have no choice but to pull the motor and inspect it. A motor shop would use a tool called a growler to check for shorted coils but you're going to have to satisfy yourself with resistance and visual checks.
     
    WorkshopChris likes this.
  18. farmer_joe Member

    Messages:
    47
    Location:
    Tonbridge, Great Britain
    I haven’t had a chance to get Into the workshop for any further investigation.

    I’ll post any findings when I do.
    Thanks for all the help.
     
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