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Thread: 1/2HP motor troubleshoot

  1. #1

    1/2HP motor troubleshoot

    I bought an old 1/2HP Craftsman floor drill press for a dedicated task. After running the tool a few times (30 minute continuous sessions), I noticed it was overheating and losing power. I would stop it, let it cool, then it would run ok for another 30 minutes. Eventually the cooling down didn't cut it and the motor would stall and hum when trying to start. I took the motor apart and found the rotor and end cap FULL of dead bees and hives. So, I cleaned it up, installed a brand new capacitor, tested the centrifugal switch, and started it back up. Now it doesn't overheat, but there is a visible spark from the bottom of the motor case (centrifugal switch area) when I start it up. There also is a faint spark when I turn it off. I can start and stop it multiple times rapidly with no problem starting - sparks every time. HOWEVER, after I use it for as long as I want (30 minutes, 60 minutes, whatever) and stop it, it won't start again. It needs to sit for an extended period (a day?) before it will start again. It does that same hum+stall; no spark. I would buy a new drill press but the jig takes forever to setup properly and would rather just get this motor fixed now that I have cleaned it and all. Any ideas? Coils didn't look burnt, though I have little/no experience inspecting motors. The pulleys spin very easily. I can even prespin them to try and help "kick start" it - they just lock the moment I flip the switch. Anyone with a better understand of electric motors have any ideas?

  2. #2
    I think the sparking you see on the centrifugal switch is normal - so let's set that symptom aside.

    So from a cold start, it now works fine? The only issue is that after 30-60 mins of use, it won't restart if it's shut off? Otherwise, everything works? Full power, no overheating, etc?

    In the condition where you've used it for 30-60 mins and it won't restart, to confirm: if you get the motor spinning by hand, then turn the power on, it locks up and hums? Is the motor actually spinning when you hit the power?

    If the motor works fine once running, but on occasion fails to start, it must be something to do with the starting circuit. A useful test would be to get the motor spinning somewhat quickly (~100 rpm) when it won't start after 30-60 mins of use, then try turning the power on and seeing if it comes up to full speed. (You might effect this by using a cordless drill with a buffing wheel or some sort of "soft" power transfer apparatus rubbing against the drill press chuck or motor pulley). If it starts, that confirms that either the starting capacitor, centrifugal switch, or start winding has a problem (likely temperature related).

    Definitely double-check all the obvious things: confirm you've got the right sized capacitor, confirm it's wired correctly, confirm the centrifugal switch is clean (run some sandpaper between the contacts, etc.

  3. #3
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    I think you are tripping the internal over temp protection when you run it for long periods of time. When it opens, it takes a while, possibly an hour or more for the internal heat to dissipate. I suggest that you check the internal air passages to see if some or all of them are blocked. You already found wasp nest and dead wasps in your motor I suspect there are more. You also should look at the contacts on the centrifugal switch and insure they are clean.
    Lee Schierer
    USNA '71
    Go Navy!

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  4. #4
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    1/2 hp 1750 rpm motors are easy to find used and fairly cheap to buy new. Why not just get a new motor and not worry about drill press motor problems for likely 20-30 years.

    Charley

  5. #5
    Dan, I like the soft transfer idea; I will definitely run that test.

    Lee, wouldn't a thermal switch kill power while it is running? Or are these common in starting circuits?

    Charles, yes it may come to that. Since I paid about the same for the machine as I would for a new motor (~$100) and I already cleaned and put a new capacitor in it, I hate to trash it now. Plus, its my first electric motor repair and the knowledge/experience always seems to pay for itself down the road...

  6. #6
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    Any time a motor gets too hot internally the thermal protection will trip even if it is running.

  7. #7
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    Quote Originally Posted by Matt Michaud View Post
    HOWEVER, after I use it for as long as I want (30 minutes, 60 minutes, whatever) and stop it, it won't start again. It needs to sit for an extended period (a day?) before it will start again.
    Hi Matt,
    It has been my personal experience that the thermal overload switch will trip while the motor is running and has reached the "shut-off" temperature. It then usually takes some time (maybe several hours or more) for the motor to cool down before the overload switch will reset so that the motor will run again. If it runs fine until you shut if off, then won't start back up until you wait a period of time - perhaps the thermal overload switch is faulty and needs replacing. Just a thought.
    David

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