Friday, May 31, 2013

V4.22 - So, your motor just up and quit?

This week we have a typical scenario from a client: “My 17 year old JJ-6CSX was running fine and then just wouldn't start. My suspects would be the motor capacitor or the starting switch, but I'm out of my element here. Any way to determine which one--or if it's something else?”

Translated, it would read like this: “My 17 year old JET jointer quit working and I’m not sure what’s wrong. I’m no good at electrical troubleshooting- HELP?” Just for the record, we are talking about a 1 horsepower single phase induction motor, which has a start capacitor.

Fortunately, troubleshooting a motor’s electrical problem is really not that difficult, but there is a standard way of doing it. First off – Keep It Simple.

Look for the easy stuff first.

1: Make sure you have power to the outlet. Try plugging the motor into a different circuit-one that you KNOW is working. Sometimes a breaker trips for no apparent reason.

2: With the power cord UNPLUGGED- check the wiring connections and make sure that one of them has not simply come loose.

3: If you KNOW there is power to the outlet – does the motor hum when you flip the switch? If it hums, that means the switch is working because there is power getting to it.

3A: If there is no humming- you’ll need to go deeper. But FIRST- UNPLUG THE POWER CORD. Then you will need to test the switch with a meter OR use a test cord that will bypass the switch, so you can plug it straight into the outlet and see if the motor runs. IF the motor runs using the test cord, replace the switch and you should be fine.

3B: Let’s say the motor does hum. Your problem is in the start capacitor or the centrifugal start switch. FIRST- UNPLUG THE POWER CORD. Now, you will need to find the centrifugal start switch. This usually requires some disassembly of the motor to find that switch’s contacts. Once you find them, vacuum the dust out if there is any. You can also blow it out with compressed air. Once you know that the switch contacts are clean, dry and contacting each other properly, try the motor again. If it still only hums, you probably have a bad start capacitor. You can replace that, OR you can take the motor to a motor shop for further testing and repair.

Motors are rather simple objects, but look for the easy stuff first. I had one customer who went thru everything on the motor, only to find out that his multi-outlet breaker strip had tripped out because of a little rainwater getting in it. (He had it on an open window’s sill) I promise he felt really dumb after that one.

Send your questions or comments to: and we’ll see what we can do to help you.

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