I assumed that the brushes were probably worn and were causing these sparks and maybe also the voltage fluctuation. I proceeded to replace the brushes and took the motor to a service shop where they resurfaced the commutator with a lathe.
After installing the serviced motor, the sparks are still there and I now find that when someone is walking/running on the treadmill the CUR LIM light comes on constantly and the motor begins to speed-up and slow-down irregularly, making a noise as if it was being forced.
Thanks again for your response.
The brushes were new but I ran the motor for about 3 hours so I assume that these would have settled by now, right? I took them out and they now have the commutator's curved shape.
This CUR LIM light is supposed to mean that the motor is drawing the amp limit from the control board. The noise is like if the motor was struggling to operate, electrical noise maybe? It is not a grinding noise or any type of friction noise nor a clicking noise. I can simulate the load, as you are asking, by just removing the belt that drives the treadmill's walking belt and operating the motor at the same spot where it is mounted. What would I be looking for with this test?
As for the bearings, if I just spin the shaft with the motor unmounted it spins freely. I would think that these are fine. I tried shifting the shaft side to side and there isn't any play. I don't have any car battery handy to try running the motor but even if I did, I would assume that it would run fine as it does with the treadmill's control board. The issue is mainly when there is load on the treadmill, that's where the sparks, the fluctuating speed and the struggle noise occur.
I did describe the symptoms to the repair shop individual but for some reason I get the sense that they are not the most competent people around, but they are the only source that I know around my area for this. Should I take it in again ask them to look for these specific issues? How would they test the winding?
Something else I am wondering is if - maybe (long shot here) the brushes aren't the right size for the motor; if, for instance, the brushes installed are wider than what is required for that motor, the brushes might be contacting more windings than necessary, increasing the current draw of the device (and perhaps causing the "struggle" noise you are hearing as the extra coils on the rotor are energized at the wrong part of the rotation cycle...?
I'd also look for any cross conducting in the commutator. After lathe trueing, you Must clean up the spaces between commutator contacts. A piece of a jewelers' saw blade works well. Smoothing/polishing after that is always good: 600 grit paper then 1000.
I would almost bet on one or more open windings on the rotor. Testing is pretty simple -- with the motor out of circuit and the brushes removed, simply use an ohmmeter to check for continuity from any one commutator segment to the segment 180° around the commutator. Each measurement should show approximately the same resistance as any other; an infinite reading indicates an open winding. Make sure that there is no continuity between any given segment and the segments directly adjacent thereto.
Ideally, the trailing edge of each segment should overhang the undercut slightly, which will help to reduce arcing (sparking).
Some info that might help. Did you take the treadmill through calibration? Did it pass?
Speculation: you need a new motor, your speed sensor needs to be replaced, or your motor control board is not communicating with the motor and its a matter of replacing some cables. There also appears to be a power issue. Its unlikely you have a dedicated power source going to your treadmill. Treadmills generally don't like to share power. They are power hogs. This could be causing the fluctuations in the voltage to the motor. It appears that you are towards needing a new motor.
I hope that this helps to clarify the subject; post back if you need further explanation...
use an ohmmeter to check for continuity from any one commutator segment to the segment 180° around the commutator. Each measurement should show approximately the same resistance as any other; an infinite reading indicates an open winding. Make sure that there is no continuity between any given segment and the segments directly adjacent thereto.
While testing for continuity, be sure to examine the commutator for proper undercutting of the mica segment separators as was already mentioned. Proper undercut will have a depth that is equal to its width,...
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