How to Troubleshoot an Electric Motor and Adjust Centrifugal Switches

Hello and welcome to Grizzly's motor 
troubleshooting and repair video. My name is   Kent and this is one in a series of how-to videos 
we're producing making it easier for our customers   to upgrade and maintain their Grizzly equipment. 
This is Shawn, an engineer here at Grizzly,   and together we're going to show you step by step 
how to easily check some common motor components   and how to adjust or replace them if needed. 
We recommend you watch this entire video and   contact our technical support at 570-546-6966 if 
you have any questions or need further assistance.   Start capacitors are connected to the start 
windings in single phase induction motors and   provide an artificial second electrical phase 
to allow starting.

They do this by storing and   releasing an electric charge that is out of phase 
with the main or run windings, which creates a   rotating magnetic field that starts the motor 
turning. This is the centrifugal switch. After   the motor starts and reaches operating speed, the 
centrifugal switch disengages and the capacitor is   no longer connected to the circuit, because it is 
only needed for starting. When a capacitor fails,   or the centrifugal switch shifts out of 
adjustment, the motor may hum without starting,   start sluggishly, or trip a circuit breaker. 
The following steps will take you through   troubleshooting these components.

inspection and testing. Disconnect the machine   from the power supply. Use caution when working 
with capacitors. They can store a significant   electrical charge even after the machine has 
been turned off. To avoid getting shocked let   the machine sit for at least five to ten minutes 
to allow the capacitor to naturally discharge   before performing any work. Motor capacitors 
are typically located outside the motor housing,   underneath a half-round cover. To access, 
simply remove the two screws that hold the   cover on and lift the cover off. As an extra 
precaution against being shocked, short the   leads on the capacitor with an insulated or wood 
handle driver. Before touching any bare wires,   the screwdriver must contact both leads at the 
same time. Be careful as there is a small chance   for an arc or spark when this is done.

Make sure 
there are no flammable materials nearby and that   you're in a safe environment where a spark would 
not cause a fire or an explosion. Now inspect the   capacitor closely for signs of damage, such as 
bulging, bursting, or leaking oil. If you see any   of these signs, the capacitor must be replaced. 
If there are no visible signs of damage, test the   capacitor with an analog or a digital multimeter. 
The meter should be set to the ohm setting. Place   the tester leads on the capacitor terminals. 
The multimeter scale should start at zero and   then rise to infinity. Here is how it looks on an 
analogue type meter. Here is what you should see   on a digital type meter. If there is no reading, 
or the reading fluctuates up and down, then the   capacitor is dead or it has an internal short 
and must be replaced. The replacement capacitor   must have the same microfarad value and a voltage 
rating equal to or higher than the original. Next   we are going to look at centrifugal switch and 
contact plate inspection and adjustment. Over   time the centrifugal switch may shift out of 
adjustment, which can cause the start capacitor   to fail.

pexels photo 5835359

To check the centrifugal switch, first 
disconnect the machine from the power supply.   Remove the fan cover from the end of the motor 
then loosen the retaining screw and remove the   fan from the motor shaft. Remove the dust cover, 
if there is one, loosen the retaining screw on the   centrifugal switch and slide the switch off the 
end of the shaft. Locate the points on the contact   plate and make sure they are in the open position. 
If they are closed, bend the circular spring flat   so the points no longer contact one another. 
If the points are welded shut, then the contact   plate must be replaced. Over time, the points on 
the contact plate can develop a blackish carbon   buildup due to the capacitor discharge during the 
startup phase. This is normal and will not affect   startup.

Look closely at the surface of the points 
for signs of pitting. Light pitting can be gently   sanded with some 400 grit sandpaper. But larger 
deformities on the surface of the points will   cause an unusable condition and potential arcing. 
If excessive pitting is detected, the contact   plate should be replaced. Now that the quality 
of the contact points has been verified, you can   reinstall the contact plate. Place the centrifugal 
switch back on to the motor shaft. Make sure the   orientation of the switch is correct so the collar 
and retaining screw face towards the fan end of   the motor. Slide the body of the centrifugal 
switch further onto the shaft until you see   the contact points barely touch each other. 
Temporarily secure the collar with the retaining   screw and mark the motor shaft with a felt-tip 
pen just above the collar. Now loosen the screw   on the collar and adjust the centrifugal switch 
further onto the shaft until it is 1/16 of an   inch below the mark on the shaft.

Then tighten the 
retaining screw on the collar. If the switch is   adjusted too far past the mark on the motor shaft, 
the contact points may not open after the motor   starts. This leads to capacitor failure, and the 
next time the start switch is turned on, the motor   will not start. Please use care when making this 
adjustment to avoid damaging the capacitor. Once   you are done, replace the remaining components in 
the opposite order they were removed. Test run.   Once assembly is complete and adjustments made to 
your satisfaction, you are ready to test run the   machine. Make sure the power switch is off then 
plug the power cord in. When you turn the power   switch on, make sure your finger is poised over 
the off button just in case there's a problem. The   motor should start and run smoothly. Well that's 
it for this video. Hope we were able to help you..

As found on YouTube

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