Capacitor motor testing

[joesal]

I have a "Precision Vacuum" pump that will not start. the motor tries to start then stops cold. I opened the casings to check for obstructions in the vacuum pump section but the shaft seems to rotate fairly easy some resistance i assume is normal due to the nature of the pump itself. I do have a capacitor or maybe even two mounted to the motor case (one of the capacitor cases has a start toggle switch to turn the motor on and off). Is there any way to check to see if I have a motor /capacitor problem or if the pump is causing the motor to stall and heat up.

[Wgoodrich]

If this capacitor is a start capacitor then you could use a continuity tester and hold it on each prong of the capacitor. First short out the capacitor while de-energized to unload it. Then touch the two prongs of the capacitor with your two test leads of a sweep style continuity tester. The tester should show full continuity. Then after holding it over time the capacitor if good condition will eventually load up and then the continuity tester will slowly go back to zero continuity. Then reverse the leads and test again. It should load again and go back to no continuity.

If this is a run capacitor then it will take a lot longer to load the capacitor and the sweep needle start falling but it will eventually go back to zero continuity once the capacitor loads.

If the needle remains full continuity forever then it tends to lead to a bad capacitor if that continuity doen't go back to full resistance or zero.

This type test is not the best but can lead you to an answer best you can do without a proper test equipment.

Properly testing a capacitor a motor shop will have a proper tester and tell you if the capacitor is bad.

Be aware to mark exactly which wires connect to which prong if you remove the capacitor and there is more than two wires connecting to that capacitor. There is infinite numbers of combinations to wire a capacitor and you must use the proper combination to re-connect your capacitor to that motor.

Hope this helps

Wg

[joesal]

after some research into the motor i disassembled the pump to see if the motor would run without any pump resistance. It ran like a top for as long as I left it on. I then pulled apart the guts of the pump and found the steel impeller body was hung up and has some scoring on it. I am now trying to hone the impeller cylinder out smooth so that I can try again.

[Wgoodrich]

Sounds like you are getting close from what you say. Let us know how you come out.

Good Luck

Wg

[joesal]

I honed out the impeller cylinder with an automotive wheel cylinder hone to deburr etc. Reassembled pump etc. Ran for five minutes clean and green with no signs of failure. I think that solved it but I still need to put a vacuum gauge on it to see if it will pull down enough.
Thanks Warren I am getting more familiar with this site as an added benefit.