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Thread: Motor Issue

  1. #1
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    Default Motor Issue

    Hi All,

    Have a problem with my lathe motor, when turned on it started to turn but seemed to struggle to get up to speed and after a few seconds it blew the fuse.
    Now getting the motor off is a bit of a nightmare and the caps are hard wired. So I'd rather not pull the motor off if its likely to be a cap problem and I'd rather not pull the caps if its likely to be a motor/ switch problem.

    I've removed the belts and the motor now starts and runs. So I'm assuming the start cap is on the way out. Does that sound right? I don't have the gear to test caps so fingers crossed the local guy is open tomorrow.

    Stuart

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    One on my mill did the same thing and ot was the capacitor.

    Dave
    Using Tapatalk

  4. #3
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    Default

    Quote Originally Posted by Stustoys View Post
    Hi All,

    Have a problem with my lathe motor, when turned on it started to turn but seemed to struggle to get up to speed and after a few seconds it blew the fuse.
    Now getting the motor off is a bit of a nightmare and the caps are hard wired. So I'd rather not pull the motor off if its likely to be a cap problem and I'd rather not pull the caps if its likely to be a motor/ switch problem.

    I've removed the belts and the motor now starts and runs. So I'm assuming the start cap is on the way out. Does that sound right? I don't have the gear to test caps so fingers crossed the local guy is open tomorrow.

    Stuart
    If it has caps it is a single phase motor. If it has caps (as opposed to one cap) it is of the high starting torque type with a centrifugal switch.

    The most likely cause for the problem that you describe is a faulty start capacitor. However, it is possible that the broken capacitor is not the cause of the failure, but only the symptom of a centrifugal switch not opening at speed. If this switch remains closed, the start capacitor will overheat in a matter of minutes and then fail. This means that you will have to remove and open the motor in order to check the function of the centrifugal switch, before replacing the start capacitor.

    You may however choose do something much better than just repair the motor. I can guarantee that you would never look back, if you were instead to upgrade to a VFD variable speed drive. Think of changing the speed on the fly whilst facing or parting, think of using your gearbox many times less frequently, think of tweaking the speed to avoid resonances and chatter whilst cutting, think of threading as slow as you want, think of the better surface finish due to less motor torque vibration, soft starting, slow jogging to check all is free before staring, higher top speed for those small diameter workpieces and plastics, faster stopping....

  5. #4
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    Default

    Hi Chris(?) Dave

    Thanks for that. Yean single phase cap start cap run(I should have said).
    I'm happyish that its not the switch as the motor sounds nasty until its prety much up to speed. Then when turned off it coasts down then you can hear the switch close. So caps out it is. I have a new run cap on the old motor(which is currently my scraper grinder/hone)

    I have a 3hp 3phase motor waiting for "one day". I've been umming and ahhing about whether to mount in on the lathe like the current one or make a separate frame. While the seperate frame maybe be good for motor vibrations I wonder if the belt tension would give you a different set of vibrations because you no longer have a torque box...or I could be over thinking things as it isnt no 10EE

    Stuart

  6. #5
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    Two questions.
    1. As the old motor only has a car rotor to get up to speed. does it even need a start cap?

    2. Is the world going to end if I replace the blown run cap 150uF with the run cap off the old motor 200-240uF?

    Stuart

  7. #6
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    Default lathe motor

    hi Stu . So you want us to guess with no testing.Um ok then.
    you don't have a muti meter?
    have you tried to help it start. spinning the chuck by hand or something
    like that. hopefully its the capacitor and not the centrifugal
    switch contacts.
    my lathe broke today as well.

  8. #7
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    Hi Aaron,

    I have a mult meter, but it doesnt have a cap checker on it.
    I didnt need to help it start(like when the start cap is completly dead)it was turning by itself, well until the fuse went lol

    What went wrong with yours?

    Stuart

  9. #8
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    Default

    Quote Originally Posted by Stustoys View Post
    Hi Aaron,

    I have a mult meter, but it doesnt have a cap checker on it.
    I didnt need to help it start(like when the start cap is completly dead)it was turning by itself, well until the fuse went lol

    What went wrong with yours?

    Stuart
    I always save the caps from burnt out motors. Seem to have half a dozen or so.

    I would just whack on one of those - should work OK. Can't do any harm.

    Pretty low tech stuff.

    Cheers

    Rob
    The worst that can happen is you will fail.
    But at least you tried.



  10. #9
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    Quote Originally Posted by Stustoys View Post
    Is the world going to end if I replace the blown run cap 150uF with the run cap off the old motor 200-240uF?
    Stuart
    Not today.... I did read recently on how to calculate start cap values, but I've forgotten already.... you won't see any difference between 150uF and 200uF however...

    The symptoms sound like it's a start cap on the way out. Just replace it and see.

    Regards
    Ray

  11. #10
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    Default yah

    ok to test a cap with out cap test function.
    conect cap to muti meter set to dc volts
    hold there for 15 sec. remove 1 lead.
    set multi meter to the greek letter
    not on the lowest scale.
    so test the cap on ohms and it will give
    you a good indication of if the cap is working.
    ie if its a dud it wont store a charge.
    i hope i have not got that backwards.

    on my lathe the end of the interlock lever pivot broke.
    the interlock lever is no longer where it should be and
    is adrift in the apron. just when i was finishing of a real
    job. lucky ive got the hercus. ILL just have to try rember
    how to cut a metric tread on it.

  12. #11
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    Default last post

    hi again. after posting the above cap test i cant help but thinking that's not right.
    you charge the cap with the multi meters ohm function and then see if there is any charge on the dc volts
    function.
    or just test the discarged capacitor on ohms it should start out with a low reading and work its way up
    towards a high ohms feading first K them M ohms.
    befor any of these tests the capacitor need to be discharged by shorting the either time. or shorting the terminals
    ie with meter in volts function.
    I dont have to tell you stu be carfull its 240v but who knows who eles may read this. so unplug befor and test befor
    touching any electrical parts.

    ITs been a long time since ive done this. ill leave the other post as a reminder to my self.
    Dont you have another fuse?

    aaron

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    Try this. Disconnect the motor from the mains - yes - obviously - disconnect at least one capacitor from the motor. Apply 12 volts from a car battery to the capacitor for about 5 to 10 seconds. Short the capacitor leads together immediately. You should get a spark, and maybe a "crack." No discharge probably means the capacitor is dead. Best test is replacing the capacitor with another motor start capacitor of about the same size. The capacitor size becomes important when the motor is starting on load, but for testing, one of about the same size will give you an idea.
    Regards,
    Alan.

  14. #13
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    Thank you gentlemen. While I can read your input while in the shed, answering on the tablet is painful at best.
    I now have a working lathe and a non working scraper grinder/hone. Was indeed the start cap.

    To answer one of my own questions above. No, even with no load on the motor it just humms with no start cap(no real surprise there really)

    Now to find the recent thread on start caps and get a new one on the way.

    Stuart

    p.s. Yes I have more fuses. though I have managed to miss place my fuse wire card... so I only have about 4 prewired ones.
    Last edited by Stustoys; 22nd December 2013 at 10:10 PM. Reason: spelling p.s.

  15. #14
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    Default

    Cap value doesn't have to be spot on Stewie, but keep it as close as possible.
    I variation will affect starting torque by an unknown amount....

  16. #15

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    Good to hear your back up and running.

    Dave
    Using Tapatalk

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