Shop Vac Surges only when turned on

Joined
Jul 13, 2020
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Lowe's shop vac. When I first turn it on (and am not vacuuming) the motor runs, then slows down and almost dies, then runs back up and does fine. There is an "electric odor" when this happens, but those are the only symptoms - no unusual noises, no screeching. Just a loud shop vac.
I took the covers off the motor as far as I could and blew the dust off but no change. It's been this way for several years.
Doesn't get used heavily - maybe 2x per month on the cars....
Thoughts????
 
Hard to say, but I used to have a box fan that did the same thing. It would start out running like something was holding it back, and as it got warmer, it would speed up. It had a dry rear bearing that would loosen up as the shaft heated up. I could occasionally hit it with some light oil, and it would start fine for a while.
 
I would say a bad bearing and likely to be a sleeve bearing. Light oil may help for awhile. I would try some oil and see if it helps. If you can see the bearing and get a few drops into it. Permanent solution is a new vacuum when this one stops.
 
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Probably the bushings starting to bind up in the motor. I've had a good run with the current Shop-Vac brand wet/dry vac I've had, but in the past, I'd be lucky to get 2-3yrs out of one before the smoke came out of the motor on them due to the bushings/bearings locking up.
 
It's been this way for several years.

Thoughts????

You should have turned it off immediately two years ago and not used it until you lubed the bearings and examined for any brush or commutator issues.

You can still do that, but now may have shorter intervals between needing to lube it again and may need to use a thicker oil to make up for the slop worn into the bearing.
 
This will be a new adventure as my knowledge of electric motors is extremely limited. I have only recently learned (thanks to BITOG) that electric motors require oiling, so I will see about disassembling the vac until I can access each end of the motor and see what oiling does.

Also will have to do some reading on brushes and commutators.....
Thanks everyone :cool:for responding.....
 
I took the motor out and turned it on. Assuming my nomenclature is correct one of the brushes looks to be rubbing against the commutator because there is a constant blueish white spark with occasional orange flecks flying off of it. I’m guessing the burned specks are the electrical smell. I sprayed some dry Teflon onto the motor bearing and it still slowed down at startup but not as much. I’m guessing the rubbing is what slows it down initially but as soon as it gets hot enough for the sparks to start flying the motor is able to spool back up and run.......

Doesn’t look good......or safe.....
 
... one of the brushes looks to be rubbing against the commutator because there is a constant blueish white spark with occasional orange flecks flying off of it. I’m guessing the burned specks are the electrical smell. ...
Both brushes should be "rubbing against the commutator," and constant small bluish sparks at the interface is normal. If you have a lot of flying orange sparks or irregular sparks, you may have worn-out brushes, or faulty commutator, or an open or shorted winding.

If you can measure the input power or current, is it the same, more, or less than normal? More would mean bearing trouble, some kind of mechanical interference, or shorted coil.
 
As I said earlier, it's probably a sleeve bearing which is permanently lubricated. Unlike a ball bearing. You can try a little oil on a sleeve bearing to prolong buying a new vacuum. But it's not to properly lubricate the bearing.
 
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