Electric motor questions

[Sal Kurban]

Greetings of the day, fellow creekers:

I have two electrical motor questions. I am in the process of rehabbing an old Delta/Rockwell 20" bandsaw with a 2 HP 230 volt motor. I changed the original motor contactor and switch and swapped them for a magnetic starter switch rated 2HP 230 volts. When I start the motor, there is a hum and vibrations but no spinning unless I give the lower wheel (no blade of course) a spin by hand. Then the motor spins fine. But it always needs that first "push" by hand. Is the capacitors bad or are these motors not suitable for magnetic starters? What else can be wrong?

Second question: I have a small DC motor 1/20 HP with 30/1 gear reduction. I noticed it starts but stops after few seconds. I took it apart and noticed one magnet was loose and the original glue gave in. What glue do I use to glue it back to the motor housing?

Any feedback from people with knowledge/experience will be appreciated.

Sal.

[Curt Harms]

The first problem is a classic failed capacitor. It could also be that the centrifugal switch is stuck open and is keeping the capacitor out of the circuit. If you start the motor by hand, let it come up to speed and shut it down, do you hear a 'click' as it slows down? If so, I'd think the switch is probably okay and you just need to replace the capacitor which should be pretty cheap as long as you don't get it from Delta but rather from somebody like McMaster-Carr. The centrifugal switch is normally on the end of the motor opposite the pulley. If you're comfortable with the idea, you could pull the cover & fan and examine the switch. Sometimes just polishing the contacts fixes the problem. No idea on the DC motor.

[Rollie Meyers]

The first problem is a classic failed capacitor. It could also be that the centrifugal switch is stuck open and is keeping the capacitor out of the circuit. If you start the motor by hand, let it come up to speed and shut it down, do you hear a 'click' as it slows down? If so, I'd think the switch is probably okay and you just need to replace the capacitor which should be pretty cheap as long as you don't get it from Delta but rather from somebody like McMaster-Carr. The centrifugal switch is normally on the end of the motor opposite the pulley. If you're comfortable with the idea, you could pull the cover & fan and examine the switch. Sometimes just polishing the contacts fixes the problem. No idea on the DC motor.

Parts from Delta are getting harder & harder to get for older Delta/Rockwell tools plus they are not cheap, even a local motor shop would be cheaper & quicker.

[Curt Harms]

Parts from Delta are getting harder & harder to get for older Delta/Rockwell tools plus they are not cheap, even a local motor shop would be cheaper & quicker.

True. When I read in another thread that Delta wanted $900 for a 2 h.p. planer motor and $300 for a starter, it was a good thing I was sitting down:eek:.

[Sal Kurban]

Thanks for the feedback. I looked at the capacitors (there are two of them) Mallory 708MFD 115 VAC. At Grainger I checked & they have Start Capacitor,590-708 MFD,110-125 VA, for $1.16 (backordered). Would this capacitor work?

[Rod Sheridan]

Thanks for the feedback. I looked at the capacitors (there are two of them) Mallory 708MFD 115 VAC. At Grainger I checked & they have Start Capacitor,590-708 MFD,110-125 VA, for $1.16 (backordered). Would this capacitor work?

Sal, that capacitor would probably work, however can't you find a better quality one than $1.16?

Regards, Rod.

[Sal Kurban]

Sal, that capacitor would probably work, however can't you find a better quality one than $1.16?

Regards, Rod.

I changed the capacitors with Dayton brand capacitors from Grainger (paid $25 for the pair) but the problem persists. Without load the motor spins with no issue. When I put the belt, it vibrates almost wanting to spin backwards. If I give it a small "hand" it will spin.
Sal.

[Charles Lent]

You likely have a defective centrifugal start switch. It's inside the end of the motor, usually the end with the wires coming out of it. You will need to remove the 4 long bolts that hold the ends on the motor. Mark the ends of the motor and the center of the motor by scratching or taping a line across the joint to help uou get the ends of the motor correctly positioned when you put it back together. Then use a screwdriver and a mallet to tap the edge of the end cover where it fits against the center part of the motor to force the two pieces apart. Work your way around the motor taping the edge of the motor end casting every few inches until it separates. The switch will be located around the shaft, but mounted in the motor end housing. Make certain that the contacts of the switch are not pitted, clean, and touching together. Now examine the centrifugal weights and actuator mechanism that's on the motor shaft. There is a plastic collar that the weights move along the shaft as the motor comes up to speed. When this happens the collar presses on the centrifugal switch and disconnects the start capacitor and start winding of the motor as the motor comes up to speed. What usually happens is that this collar gets stuck and does not return to it's position as the motor slows down, so it never allows the centrifugal switch to close and re-connect the start capacitor and start winding to be ready for the next time that you try to start the motor. To fix it, clean the shaft where this collar must slide and apply a thin layer of light motor or or machine oil, then re-assemble the motor. If the switch contacts are good, you have a good start capacitor, and you have lubricated the centrifugal mechanism, the motor should start. The only other thing that may be wrong is a damaged start winding in the motor. If this is the case you may be in need of a new motor. An electric motor shop should be consulted for help with this.

Charley

[Sal Kurban]

Thanks for the replies and the detailed instructions; it turns out neither the capacitors nor the centrifugal switch is the problem. I contacted Delta, the motor is so old that they referred me to Marathon electric which had produced it. I contacted Marathon and they sent me the rwiring diagram and detailed specs for capacitors etc. The motor has a short somewhere as it still stalls and trips the breaker or resets the magnetic switch. I ended up buying a used Dayton Motor for replacement. The Dayton is a 2 HP TEFC farm duty model # 1TMX6A. Even though the original was a 145T frame, and the new motor is 182T, the mounting plate has holes for motors with both frames so no problem there. Just an update for the record.
Sal.

[Charles Lent]

I didn't suggest that the winding might be bad because it is so rare to have this kind of problem. It's usually a problem with the capacitors or the centrifugal start switch. Have you carefully inspected the windings? If there is a short in the windings it is frequently right where the wire enters the metal of the stator and it can be repaired by re-positioning the wire and adding a dab of silicone or insulating varnish. Other times the wire splices can contact the metal case and short out. A shorted winding deep inside where you can't repair it without re-winding the motor is extremely rare. If re-winding is required, then it in most cases will be cheaper to replace the motor. Only very large motors and motors that have special frames are worth the cost of re-winding.

Charley