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  1. #1
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    Default Single phase motor - runs but bad vibration

    The motor is off an old Atlas drill press. It worked when I got it, but was quite noisy. Bearings were a bit rough and the motor pulley had been butchered and was running eccentrically so I pulled it apart and replaced the bearings and sort out the pulley mounting.

    I've put the motor back together and just ran it on the bench but it vibrates badly.

    It feels to me like its electrically unbalanced when running, and if I run it for 30secs the case and capacitor are warm to touch.
    The capacitor is labelled as a start cap, 200-240uF 250vac.
    Its got a centrifugal start switch, and definitely doesn't start if I remove the switch actuator.

    The wiring is definitely not original, so I'm now at the point of "assume nothing".

    Firstly - does anyone recognise what brand/type of motor it is? There's no data plate on it.



    Secondly, any suggestions for initial troubleshooting steps or likely issue before I start removing connections and working out how the windings/cap/switch are connected?

    Steve

  2. #2
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    Default

    Do you here the centrifugal switch engage / disengage when it slows / starts.
    If the cap is warm maybe it’s remaining in circuit ?

    Also does it run with switch disconnected and spin the shaft ?

  3. #3
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    Hi Steve,

    The capacitor should not get warm under any circumstances ! The centrifugal switch should disconnect the capacitor and start windings if it is working properly. On some motors the centrifugal switch can be moved back and forth on the rotor shaft to set the correct position.

    I've worked on motors where the securing screw for the centrifugal switch has become loose allowing the switch to move and stop working. This causes the motor to overheat and running rough is a symptom of this, as is a bad capacitor.

    I've also seen motors where some idiot has broken off one of the rotor fan blades, causing an out of balance condition. Breaking off a blade opposite to the missing one sometimes works if the broken blade has one directly opposite. Otherwise it is a proper rebalance job !


    Motor-Cap_start.png
    This circuit might help.

    HTH.
    Best Regards:
    Baron J.

  4. #4
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    Default

    I can definitely hear the weights click back as it slows, but can't confirm it's actually switching.

    Good thought on a spin start. I'll give that a crack and see what happens.

    Steve

  5. #5
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    Default

    Thanks BaronJ.
    The fan actually has a bit of blade broken off, but I've tried running with and without the fan and no difference.
    Have also tried adjusting the preload on the switch, but can't get a change in behavior.

    I'll have a go at the spin start test next as that will isolate if it's a start circuit issue.

    Steve

  6. #6
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    Hi Steve, Guys,

    Sometimes the weights click but doesn't actually do anything because the contacts are welded together.
    Best Regards:
    Baron J.

  7. #7
    BobL is online now Member: Blue and white apron brigade
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    Default

    It looks like an motor similar to one I messed around with about 10 years ago except mine had run and start caps.

    I bought mine from gumtree for $25 and it too had no nameplate and I think it was of Chinese origin. Before handing over the $25 I tested out the insulation which was OK and it seemed to run fine for the brief period I tested it, but eventually I found out probably why the seller was happy to get rid of it.

    When I got it home and ran it under no load while monitoring current with an ammeter the motor drew more current, and both the motor and run cap got warmer, than I expected. The problem got even worse when I put it under a bit of a load whereby it got hot within a couple of minutes. I play around with a couple of different run caps and finally found one that seemed to run a bit cooler and decided to leave it free running for about 30 minutes during which time the motor and cap got very hot and the cap started swelling and smelling so I turn it off. I replaced the cap and it did the same thing. I just think maybe they are very inefficient motors and not designed to run continuously.

    In the end I scrapped it.

  8. #8
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    Hi Guys,

    I've seen some like that ! Often the insulation has been damaged somewhere on the windings. A scrape or a knock, sometimes you can see where the enamel on the wire is damaged or missing. Often the rotor has not been removed very carefully. Allowing it to catch the windings and causing a short between turns.
    Best Regards:
    Baron J.

  9. #9
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Hi Guys,

    I've seen some like that ! Often the insulation has been damaged somewhere on the windings. A scrape or a knock, sometimes you can see where the enamel on the wire is damaged or missing. Often the rotor has not been removed very carefully. Allowing it to catch the windings and causing a short between turns.
    A similar thing can happen inside the windings. Motor overloaded and run too hot - this causes hot spots inside the windings producing a short between turns - these are difficult to detect let alone fix.

  10. #10
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    Thanks guys.
    Unless I can get it to run smoothly from a spin start I'll probably just cut my losses and salvage the new bearings before tossing it in the scrap. Its just not worth investing a bunch of time into.
    I've salvaged a .55kW 3 phase motor from a fume extractor the other day. Already set for 240v and I've got a small VFD here to suit. Probably a better setup for the drill press anyway but I didn't want to take on the setup right now. Hence just trying to get the original motor running so I can use it.

    Steve

  11. #11
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    Bugger. The smoke got out.
    I guess that makes the decision to bin it pretty clear

    I'd say it's had issues and definitely already been messed with. The start capacitor wires were connected by twisting and then insulated with tape.

    Isolated the main winding and ran it on that - it started by itself which I didn't think it should - but still had the vibration.
    Ran for about 30secs before the magic smoke started oozing out the ends and I pulled the plug on it.....

    Steve

  12. #12
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    Default

    Sounds like you need a jar of this.

    lucassmoke.jpg

    Tony

  13. #13
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    Yeah - it's good stuff. Damn hard to get in the ends of the wires though

    Steve

  14. #14
    BobL is online now Member: Blue and white apron brigade
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    Sorry to hear that but it really does sound like it had an internal short of some kind.

  15. #15
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    Thanks Bob - I agree.
    Its a minor setback as I was hoping to cross it off the TODO list, but its probably for the best in the long run.

    Steve

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