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Thread: Unisaw motor help

  1. #1

    Unisaw motor help

    Hi all!


    Last fall, I acquired a Rockwell Unisaw 34-466 (mid-late 70's). At the time I had no way of testing it out, but took it with the idea that being a project could be fun.


    Flash forward to now, and I am so close to having the machine up and running after a _long_ list of replacement parts and repairs. The problem that needs addressing this time is with the motor (Rockwell 83-651: 1ph, 3hp, wired for 230v) / electrical.


    The saw has new cords (magnetic switch to electrical box, motor to electrical box, electrical box to outlet). Initially, the motor turned on and off with only a slight lag and hum. I assumed the start capacitor might needed to be replaced and because the motor is still outside the cabinet, now seemed like a good time to do it. Well, the old capacitor specs were printed on a paper label that over time bled and faded and are completely illegible. An internet search revealed someone else with the same motor set up who provided the specs on their capacitor so I purchased a similarly spec'd model. (220-250 VAC, 270-324 mfd)


    I installed the new capacitor today and now nothing. Wrong capacitor? If so, what specs should I look for? I'd love to have this saw up and running as soon as possible. Thanks for any advice!

  2. #2
    Join Date
    Oct 2007
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    You might try over at OWWM dot org (Old Woodworking Machines) Everything Electrical forum. Lots of experience there.

  3. #3
    Join Date
    Sep 2016
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    Dust inside the starting switch internal to the motor is a common problem.
    Bill D.

  4. #4
    Update: I ended up checking the connection to the new capacitor and it might not have been on so well. Made sure the connection was good and tried again.

    I now get the hum again, but nothing moves. I can give the pulley a little push and it does spin, but would take 1˝ to 2 seconds to make a revolution. Or it would if the breaker didn't trip before one full turn.

    Thoughts, anyone?

  5. #5
    Join Date
    Mar 2013
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    North Alabama
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    There's some small chance that the new capacitor is faulty as well, but as Bill D. suggested, the centrifugal switch inside the motor may need a good cleaning.
    Chuck Taylor

  6. #6
    Try this. Wrap a thin rope or twine around the shaft. Turn the power on and then pull the rope to give the shaft a good spin. See if the motor spins up to speed.

    If so, something is wrong with the starting circuit: Either the start capacitor is bad, the centrifugal switch is not closing, or your starting coil is bad.

    If it doesn't spin up to speed, you have some other problem, for which I have no suggestions right now.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  7. #7
    "Wrap a thin rope or twine around the shaft. Turn the power on and then pull the rope to give the shaft a good spin. See if the motor spins up to speed."

    Tried this and the motor spun right up! So....

    If it's the start capacitor, is the new one I put on even the right one? (See OP for specs)

    If the centrifugal switch isn't closing, how do I remedy that? Same for the starting coil?

    I'll add that after shutting the motor down, starting it back up again a minute or so later tripped the breaker. Don't know if that helps diagnose anything, but thought I'd add it here just in case. (The wiring in the building should be good. It was redone about 6 months ago and the electrician was able to see what kind of power requirements this motor needed.)

    Admittedly, dealing with this kind of stuff is not my forte so I really appreciate any help (particularly when it's descriptive)!

  8. #8
    Join Date
    Dec 2010
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    I would take it to a motor shop. They will be able to fix anything short of fried windings, efficiently and correctly. I would have them change the bearings, too, and then you likely won't have to worry about the motor for 25 years or more.

    John

  9. #9
    Quote Originally Posted by phillip kerrigan View Post
    "Wrap a thin rope or twine around the shaft. Turn the power on and then pull the rope to give the shaft a good spin. See if the motor spins up to speed."

    Tried this and the motor spun right up! So....

    If it's the start capacitor, is the new one I put on even the right one? (See OP for specs)

    If the centrifugal switch isn't closing, how do I remedy that? Same for the starting coil?

    I'll add that after shutting the motor down, starting it back up again a minute or so later tripped the breaker. Don't know if that helps diagnose anything, but thought I'd add it here just in case. (The wiring in the building should be good. It was redone about 6 months ago and the electrician was able to see what kind of power requirements this motor needed.)

    Admittedly, dealing with this kind of stuff is not my forte so I really appreciate any help (particularly when it's descriptive)!
    Let's assume the starting cap you put in is good and you installed it correctly. The next most likely problem is dirt in your centrifugal switch keeping the switch from closing. You have to take the end off the motor (the end opposite the driving shaft) to get to the centrifugal switch. By hand, open the switch and make sure there's no swarf between the contacts. Take some fine sandpaper and lightly burnish the contacts. Put back together and try the motor again.

    If that doesn't work, I'd try another start capacitor (make sure it's the right size) and make sure it's connected properly. If that doesn't work, take it to a motor shop.

    Mike

    [Starting coils don't go bad very often. It's highly likely your problem is either a starting cap (probably 90% of the time) or swarf in the centrifugal switch (more than 9%, but not 10%).]
    Last edited by Mike Henderson; 05-05-2021 at 4:00 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  10. #10
    Thanks for the well explained advice!

  11. #11
    Join Date
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    I think you’d spend a few hundred bucks at a motor shop, if they’d even work on a little toy like that (to them). Do some research and fix it yourself. Looks like you going down that road.

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