Capacitor Replacement

[ShSLarry]

My shopsmith Mark V (~1985) will not start. Motor is getting power, cord is good, new switch installed, but still the motor doesn't run. Just 'dead'. Could the capacitor be bad. I haven't taken out the motor yet, just looking for a likely suspect.

[DLB]

My shopsmith Mark V (~1985) will not start. Motor is getting power, cord is good, new switch installed, but still the motor doesn't run. Just 'dead'. Could the capacitor be bad. I haven't taken out the motor yet, just looking for a likely suspect.

Welcome to the forum. Generally on Mark 5/V motors the mechanical (centrifugal) start switch is the likeliest suspect. Airflow is through the motor, carrying contaminants and especially sawdust. It builds up on the switch contacts until there is no contact. A start capacitor can also fail, but is less common. Maybe way less common. With either of these, one would expect an otherwise good motor to hum but not rotate, and possibly trip a circuit breaker. It is critical to not let it hum without rotation for long. Good luck!

- David

[JPG]

Does it hum when turned on? Or is it truly dead?

[steverboss]

Just bought a used Mk V from 1981, motor was apart. Put back together & it just hums but doesn’t spin. Likely the centrifugal switch because I replaced the capacitor & no change. It’s the GE 1 1/8 HP motor. How do I identify & locate a replacement centrifugal switch? Everyone talks about this switch, but nobody mentions where to get a replacement. Search shows lots of centrifugal switches but not the same. It doesn’t appear to be expensive.

[jsburger]

The switch normally does not need to be replaced. Usually the contacts are just dirty and need to be cleaned.

[steverboss]

Ok, I’ll try that first, then let you know.

[steverboss]

Here is a really good video that explains how the start & run circuits work in single phase motors similar to the ones used in our Shopsmiths. It explains how the centrifugal switch works. It’s is common that when the contacts in the centrifugal switch get dirty or burnt, then the motor just hums when you turn it on, but won’t spin. That’s because only the “run” windings are energized and NOT the “start” windings. So, don’t leave the motor on for more than a few seconds in this situation, because it will burn out the “run” windings. Anyway, enjoy this video.

https://youtu.be/dvx5NkEWNq0

[benmcn]

Jacob Anderson has a video about the AO smith 3/4 horsepower motor. After he retired he made all of his repair video available. For a complete list of all of his repair videos you can visit his web page. If you scroll down to the bottom you will find links to videos covering the other electric motors that ShopSmith has used.

Here is the link to his web page:
https://jacobvb.wordpress.com/youtube-videos-2/

Below are the links to the variety of motor rebuild he has made available.

GE/AO Smith ¾ hp motors:
https://www.youtube.com/watch?v=yczsPTHdpT8

Franklin 3/4 HP Motor Rebuild:
https://www.youtube.com/watch?v=-T8qkbvV9Ps

1-⅛ hp Emerson, US motors, GE round back or AO SMITH round back motors:
https://www.youtube.com/watch?v=EJkhA8XmrKs

1-⅛ hp GE box back, AO SMITH BOX BACK (both ¾ hp and 1-⅛ hp), and ¾ hp AO Smith box back motors: https://www.youtube.com/watch?v=K6uo-LHJHgI

[Duckman]

In case anyone is interested. The original capacitor worked. I disassembled the motor, cleaned it up, replaced the bearings, put shrink tubing on some of the old wiring, hooked up the capacitor, put on a temporary cord, and plugged it in. The capacitor started the motor running, the centrifugal swtich worked like it was supposed to once the rpms got high, and it ran. Eventually ran the motor for 30 minutes and it seemed to do great. I did not need to replace the capacitor. Next step is to CAD design a capacitor housing replacement and get it 3d printed.