Any ac motor techs in here

[Drkuhar]

My drill press motor has a split phase non capacitor 1/2 hp motor on it. For the past couple of years it would hum and you had to spin start it, but you could start either direction. I removed it and took the cover off the bottom and blew it out the centrifugal switch and upon bench testing it. It will start on its own now but it reverses direction each time it powered up.
Example plug it in spins clockwise unplug it wait for a complete stop plug it in and spins counter clockwise back and forth. Occasionally it still hums and need spun to start. This is a simple two wire motor with a chassis ground

I have already put a new motor on the drill press but if this could be fixed easily for a spare I would hang onto it. If not its going to be stripped and junked

 

[blk7gxn]

....researched and found this answer for you, hope it helps!

There is a centrifugal switch in your motor that switches the start cap in and out. At rest the switch is supposed to be closed so that when you apply power, the start cap is in the circuit and creates a virtual phase shift in the magnetic field that causes it to spin in the desired direction. Once it gets to speed, the centrifugal switch opens and removes that cap, but the motor is already spinning so it keeps spinning in that direction.

If that switch fails to re-close after the motor is shut down, the start cap, even if good, will not be in the circuit. So then what happens is that the run winding field field is randomly going to spin the motor in either direction. Murphy's Law then takes over to dictate that it will always be the WRONG direction.

If there is no centrifugal switch, then the function is being done by an external device called a "potential relay" that is looking at the back emf of the motor to decide when to switch out the start cap. But he same holds true, it is likely failing open.

 

[Drkuhar]

....researched and found this answer for you, hope it helps!

There is a centrifugal switch in your motor that switches the start cap in and out. At rest the switch is supposed to be closed so that when you apply power, the start cap is in the circuit and creates a virtual phase shift in the magnetic field that causes it to spin in the desired direction. Once it gets to speed, the centrifugal switch opens and removes that cap, but the motor is already spinning so it keeps spinning in that direction.

If that switch fails to re-close after the motor is shut down, the start cap, even if good, will not be in the circuit. So then what happens is that the run winding field field is randomly going to spin the motor in either direction. Murphy's Law then takes over to dictate that it will always be the WRONG direction.

If there is no centrifugal switch, then the function is being done by an external device called a "potential relay" that is looking at the back emf of the motor to decide when to switch out the start cap. But he same holds true, it is likely failing open.

Looks like i need to take the centrifugal switch apart and clean the contacts. I dont have a starting capacitor but everything else sounds right about the random direction starting
Thanks

 

[blk7gxn]

Looks like i need to take the centrifugal switch apart and clean the contacts. I dont have a starting capacitor but everything else sounds right about the random direction starting
Thanks

Your very welcome!

 

[Tomeal]

Might not apply in this case, but the humming and no spinning, sometimes can be a dead spot. Spin the motor and it takes off. It's really random for the motor to stop on the dead spot, but explains why it runs once moved off the dead spot.

 

[Drkuhar]

Well took apart the switch , cleaned contacts made sure everything moves good. Takes off great no hum at all, runs really torquey. But still switches direction everytime it powers down and back up . I think the start windings (no capacitor) must have a short in it somehow. Wonder if spin starting it for as long as i did caused issues

 

[Tomeal]

If there is a short in the windings you should get contiunuity to ground from one of the windings.

 

[Drkuhar]

If there is a short in the windings you should get contiunuity to ground from one of the windings.

On the two leads that go to the switch in the back one i can get continuity to the power plug leads and the other is dead. No continuity to ground or any other wire I probe. It like it broke connection and isnt hooked to anything

 

[Tomeal]

I'm used to testing HVAC motors. I usually encounter capacitors.

I've not ran into centrifugal switches.

To check windings you need to eliminate any other switches. With a capacitor I can check each side of the electrical connector to case ground. If you get contiunuity, it is shorted.

Your case I'm not sure which side of the switch would go to the windings?

I might be leading you in the wrong direction? Just tryin to throw thoughts out there?

 

[Drkuhar]

This is the simplest motor ive iver tore into but it is not obvious whatever it is. There is only 2 lines going into the motor and 2 lines at the switch, no obvious burnt lines, plenty of power when it runs but the starting issue has me think its a broken wire thats not shorted out just broke and not completing the starting circuit.
Here a pic with the centrifugal part off. The two leads on that switch. One has continuity to the plug in, one is dead with no continuity to anything. The switch itself works fine.
Its about ready to be the start of my next copper ingot lol