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oldwoodie

Simple motor chesk saved two electric motors

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Motor on Powermatic cabinet saw would do nothing but hum when turned on. Here's what I did: I bought a volt/ohm meter since my other one was defective. Checked out Youtube on how to check capacitors, confirmed that they were good, pulled end of motor, found points were burned, took 600 grit sandpaper, shined points, reinstalled endcap, fired it up. It ran so sweet that I decided to check my 5hp motor on planer that had been sitting for several weeks waiting on a good deal on a new one of even a used one. Guess what! I found the same thing wrong with this one! When I connected it to a tempory power source, all I could do was praise God for His goodness! Then, the thought came to me: I wonder how many electric motors are thrown away or carried to an electric motor shop and pay a hefty price for a simple repair that almost anyone can do at no cost! Well, this leads me to another motor that has been laying around for a few weeks, but I haven't had time to check it out. Will try to remember to let you know what I find. Hope this helps a lot of folks save money on repairs.

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  I have found similar issues and try to go over my power tools at least once a year.

3 hours ago, oldwoodie said:

I wonder how many electric motors are thrown away or carried to an electric motor shop and pay a hefty price for a simple repair that almost anyone can do at no cost!

 I am probably guilty of this. Glad you were able to solve the issue.

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Centrifugal switch function.

When the motor is OFF and at rest, the points on the contact plate are closed. When the motor is started, current is sent to the start capacitor, through the closed contact plate points, and then to the motor start windings to get the motor up to full speed as fast as possible. When the speed of the motor shaft gets close to the rated motor speed, centrifugal force causes the flyweights to override actuator spring tension, swing out, and open the contact points. When the points are open, current is cut to the start windings and the start capacitor, allowing them to cool. At this point, the run windings take over and operate the motor. (Note: Often a run capacitor is used in the run circuit to increase motor efficiency.) When the motor is turned OFF, centrifugal force diminishes, and the springs draw the flyweights back in (sometimes with a click sound), returning the contact points to the closed position.

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i barely got a C in my one course on electrical engineering. i'm sure that what you wrote is correct, but that doesn't mean i understand where i would go looking for points in a motor tomorrow.

 

i plug it in, i hit start/on, it better work!

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45 minutes ago, DAB said:

i barely got a C in my one course on electrical engineering. i'm sure that what you wrote is correct, but that doesn't mean i understand where i would go looking for points in a motor tomorrow.

 

i plug it in, i hit start/on, it better work!

 

Yes, most are on the fan end.  Try blowing the dust out of it with air before taking it apart.  Dust can get in the works and keep the points from closing.

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3 hours ago, DAB said:

and for those of us who are unlearned regarding electric motors, would you care to explain what a 'point' is, where they are located, what they do, and what goes wrong with them that needs fixing down the road?

all-about-electric-motors-fa.pdf

Electric Motor Troubleshooting.pdf

Part #12 is the switch...

 

M3.jpg

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