Jointer motor revisited

[John T Barker]

I posted earlier about my jointer motor which has problems. It hums when I turn it on but will only run if I push the belts a bit. It is a 50+ year old machine. Some of you offered that if I posted pictures of the motor you might be able to tell me if I can replace the capacitor or just go for a new motor. Here they are. Hope it helps.


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[Bryce Adams]

That motor doesn't have a capacitor. The trick with a single phase motor is getting it to start spinning. The most common way is to have a start winding to provide starting torque. This winding can only be energized during starting, or it will burn up. So it's connected through a centrifugal switch while the motor is stopped, and the switch opens as the motor comes up to speed. If that centrifugal switch sticks open, you don't have the start winding in the circuit and the motor doesn't develop any torque to begin spinning. If you push on the belt, you provide the starting rotation, and the motor takes off.

(As an aside, on many motors you can hear the centrifugal switch click closed as the motor spins to a stop.)

A start capacitor on a motor is connected in the start winding circuit and increases the starting torque for a motor starting under load. If a starting capacitor fails, you can have a similar situation with insufficient torque to start the motor, but your motor doesn't have that.

You may be able to open up the motor and simply clean the switch to get it working again. Or it may have to be replaced. It's also possible that the switch is fine and the start winding failed open. When I'm trouble-shooting, I like to start with the easiest, least expensive possibility first.

I've got a Delta Unisaw from the '40's and I'm currently replacing the motor bearings in it. That's an entirely different deal called a repulsion motor with a commutator, brushes, and a wound-rotor. From your pictures, I don't think that's what you have.

Good luck,

[Judson Green]

I think you have a repulsion induction motor. Probably not too hard to take apart and see about fixing the centrifical switch, but that may not be the problem. And if it is, the part might not be available. So, I'd also be looking on craigslist for a replacement. You could probably get away with a 1.5 HP.

Good luck