Electronics > Repair

Any way to fix this motor?

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calzap:
The motor is a 3 HP, 240 VAC, 1 phase, TEFC motor made by WEG.   It powered a two-stage centrifugal water pump.  The pump/motor started making a loud racket …  like gears grinding.  Noise seemed to emanate from the motor rather than the pump.  Externally nothing looked amiss.

Unfortunately, the design is that an extension of the motor output shaft is the pump shaft.  The only way to get a thorough look inside the motor was to remove the pump from the shaft, which meant the pump had to be completely disassembled.  This was done, and with a bit of study, the probable culprit emerged.

The centrifugal starting switch assembly spins freely on the motor shaft when it should be fixed to the shaft.  Figure 1 shows the shaft and parts on it.  The shaft in the pics turns the cooling fan; it is not the output shaft, which is at the other end of the rotor.  Looking at the shaft starting on the left is a flattened area for fan attachment (fan has been removed).  Next is the bearing assembly.  Next is the centrifugal switch assembly, which I believe is in the position in which it is supposed to be fixed to the shaft.  Next is an external retaining ring.  Finally, there is the rotor.  No loose parts or pieces of parts were found inside the housing.

I believe the metal ring of the centrifugal switch was force-fitted on the shaft, and the role of the retaining ring was to limit how far the centrifugal switch could be pushed on to the shaft during assembly.  With time, thousands of starts and about 3000 hours total running time, the metal ring of the centrifugal switch started slipping.  Now the whole assembly spins freely on the shaft, has a slight wobble, and can move back and forth on the shaft.  See Figure 2.   The motor still starts because the default still-condition is for the starting coil and capacitor to be engaged.

The loud racket is because there is some friction between the metal ring of the centrifugal switch.  So, it spins as the shaft turns, but as it does, its flyweights hit the tabs on the retaining ring.  See Figure 3.  The tabs show evidence of such collisions.  Because the centrifugal switch assembly can move back and forth along the shaft, it bounces between the bearing assembly and the retaining ring (ouch!).

If I could remove the bearing assembly, I could slide the centrifugal switch off the shaft.  Then drill a couple of small holes in its back plate and wire it to the tab eyes of the retaining ring.   The bearing assembly also appears to have been force fitted to the shaft.  Even if I could remove it without damage, getting it secured in position again would be problematic.  I don’t know of an adhesive that I would trust to secure the metal ring of the centrifugal switch assembly to the shaft.   Any ideas?

  Mike in California
 

calzap:
I just realized that fixing the centrifugal switch assembly to the retaining ring might not work because the retaining ring might start spinning freely on the shaft.    How about removing the centrifugal switch assembly completely and using an external timing circuit to cutout the starting coil and capacitor a few seconds after power is applied?

Mike in California

BrokenYugo:
Perhaps a tack weld or two? That or epoxy it on with a really good prep job, probably best to press the bearing off in that case, I'd just weld it.

calzap:

--- Quote from: BrokenYugo on December 04, 2021, 07:05:35 pm ---Perhaps a tack weld or two? That or epoxy it on with a really good prep job, probably best to press the bearing off in that case, I'd just weld it.

--- End quote ---

I thought about welding the metal ring to the shaft with my MIG welder.  But doing that with the centrifugal switch assembly on the shaft might result in heat damage to the pusher plate (it's plastic).   If I could get the bearing off the shaft, then pusher plate could be removed temporarily and welding could be done then.   The bearing would have to be pulled off.  Perhaps a steel disk with a slot could be put behind it and then I could use a gear puller.

Mike in California

james_s:
I had this happen with the metal cooling fan in a dishwasher pump motor, dribbling some superglue on it would help for a while but eventually it would break loose again. I ended up getting a nearly new dishwasher for free so I gave up trying to fix that one.

I can think of a couple of ways you might be able to fix this. Since you have a MIG welder probably the easiest is to weld it, just a quick tack weld in a couple of places ought to do the job so heat shouldn't really be an issue. Another thing you could try is take a sharp punch and hammer and punch a series of dings around the press fit lip to tighten it up on the shaft. You might also be able to drill and tap a hole and put a small screw in it, but the shaft may be pretty hard steel and the space is cramped.

Welding would be my vote as the easiest and most likely to last. Just remove the springs and slide the plastic part as far away as you can and give it 2 or 3 zaps, just little tack welds. Maybe a combination of the punch and tack welds, I don't think it will go anywhere then.

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