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Thread: 3 Phase motor stalling

  1. #1
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    3 Phase motor stalling

    The 1hp 3 phase motor on my lathe, (1948 South Bend 13) stalls occasionally. This is with light cuts, easy feed in on parting cuts, nothing I ever had a problem with previously.
    So the question for those with electric motor experience is:
    Why does that happen, or is this motor showing signs of eminent death?
    Ernie F.

  2. #2
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    Re: 3 Phase motor stalling

    Either a loose connection on one ohase, voltage drops from supply, or a bearing seizing up.

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    Re: 3 Phase motor stalling

    Quote Originally Posted by metalman21 View Post
    The 1hp 3 phase motor on my lathe, (1948 South Bend 13) stalls occasionally. This is with light cuts, easy feed in on parting cuts, nothing I ever had a problem with previously.
    So the question for those with electric motor experience is:
    Why does that happen, or is this motor showing signs of eminent death?
    Is it hooked up to 3 phase power or is it running from a converter. In general a 3 phase motor will run at greatly reduced power on 2 phases. It is common for a thermal overload or a fuse to be not working on one phase. Most of the ones I have seen that this has happened on you can tell by one or more of these signs. 1.reduced rotational speed , 2 a louder hum from the motor , 3 the motor runs hot. Check power at all 3 wires to the motor.

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    Re: 3 Phase motor stalling

    Quote Originally Posted by Woznme View Post
    Either a loose connection on one ohase, voltage drops from supply, or a bearing seizing up.
    I’m beginning to suspect the F-R drum switch as possibly worn, dirty or otherwise faulty.
    Ernie F.

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  8. #5
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    Re: 3 Phase motor stalling

    Quote Originally Posted by thegary View Post
    Is it hooked up to 3 phase power or is it running from a converter. In general a 3 phase motor will run at greatly reduced power on 2 phases. It is common for a thermal overload or a fuse to be not working on one phase. Most of the ones I have seen that this has happened on you can tell by one or more of these signs. 1.reduced rotational speed , 2 a louder hum from the motor , 3 the motor runs hot. Check power at all 3 wires to the motor.
    It is hooked to true 3 phase service, no converters. I checked the voltage with a meter at the main service and at the twist lock outlet that feeds the lathe. Averaged 240 volts across any pair of the outlet contacts.
    i did lose a phase a few years ago when a squirrel toasted himself up on the service pole. The lathe and the mill wouldn’t even run with that phase knocked out.
    i will check at the motor and the switch.
    Last edited by metalman21; 06-24-2020 at 07:54 PM.
    Ernie F.

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    Re: 3 Phase motor stalling

    Also might try checking continuity between windings with the power off to see if anything funny is going on between them. You should get no continuity.

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    Re: 3 Phase motor stalling

    Take the belt off. With it running, check amperage each phase. If you have the know how to do it safely, check voltage on each phase to ground while running.

    Turn it off, lock out the power source. Depending on whether it is dual voltage. Make a diagram of the way it was connected. You have three or six windings. They will be connected series, high voltage, parallel low voltage. Three windings may be connected at one end internally. three others will have both ends in the wire box.
    With an ohmmeter, or better still a megaohmmeter, you are looking to compare the windings. Three interconnected you can only check two at a time. check each combination of these, compare. The three double ended, compare.
    Check each lead for continuity to the motor frame.

    A difference in the winding resistance suggests winding problems. A difference in voltage says power source issues. Current difference might be either, or both.
    Three phase motors are subject to damage if all three legs of supply aren't equal or close to it.
    Last edited by Willie B; 06-24-2020 at 08:33 PM.
    An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.

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  12. #8
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    Re: 3 Phase motor stalling

    Is the belt slipping? Might need some spray grip if it is. My belt was leather. Bob

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    Re: 3 Phase motor stalling

    Check the drum switch.
    Typically this where you find the problem on old tools .

    Dave

    Quote Originally Posted by metalman21 View Post
    The 1hp 3 phase motor on my lathe, (1948 South Bend 13) stalls occasionally. This is with light cuts, easy feed in on parting cuts, nothing I ever had a problem with previously.
    So the question for those with electric motor experience is:
    Why does that happen, or is this motor showing signs of eminent death?

  15. Likes William McCormick liked this post
  16. #10
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    Re: 3 Phase motor stalling

    Metalman. Did you say 240 volts, should be around 277 a-b,a-c,b-c, ground to leg should be 480.

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    Re: 3 Phase motor stalling

    Sorry I got those numbers backward,

  18. #12
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    Re: 3 Phase motor stalling

    Oops, now guessing you got 3 phase 240. Got to get new meds or more booze.

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  20. #13
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    Re: 3 Phase motor stalling

    Check prices for Drum switch on Amazon.
    Drum switch can be rebuilt but it is hard to over the internet.

    Dave

    Quote Originally Posted by metalman21 View Post
    The 1hp 3 phase motor on my lathe, (1948 South Bend 13) stalls occasionally. This is with light cuts, easy feed in on parting cuts, nothing I ever had a problem with previously.
    So the question for those with electric motor experience is:
    Why does that happen, or is this motor showing signs of eminent death?

  21. #14
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    Re: 3 Phase motor stalling

    I removed the cover from the drum switch and inspected. Didn't look bad or burned, I cleaned the contact surfaces with carb clean and grey Scotchbrite. Have to see what happens on the next job.
    I scored a spare motor (cheap) for this lathe years back and I thought that would guarantee the original motor would never go bad!
    Thanks for all the tips. I'll update this post with any results.
    Ernie F.

  22. #15
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    Re: 3 Phase motor stalling

    Quote Originally Posted by rhunt View Post
    Is the belt slipping? Might need some spray grip if it is. My belt was leather. Bob
    you
    I think you called it. The belt lacing was giving up, nylon/rubber belt is still good. I trimmed the ends and installed a new lace connection, reinstalled and adjusted. I'll see next job soon.
    Ernie F.

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