electric motor sparking

My Might Mite vacuum cleaner was grinding and starting to smell. I took it apart and ran the motor and saw tons of sparks streaming out of the area where the brushes make contact. I removed the brushes and found that there was tons of graphite left. Is my Mighty Mite junk?

Does the contact face of the brush(es) have one continuous arc from contact with the armature?

Are the ends of the brushes pitted? Are the springs or brush holders keeping them seated properly? How does the commutator surface look? There are a lot of reasons for a motor to spark. Can you see the electrodes when you look at the end of the brushes, sometimes even when they look like there is a lot left, they’ve worn down enough to expose the lead inside the brush (at least with larger motors I’ve seen that).

Having purchased three inflatable beds in the last year and having noticed that all three of the included electric pumps appear to do their own, barely contained fourth of July impressions, I am also interested in this question.

Depending on the type of motor the sparking may be normal. Ideally there wouldn’t be any of course, but many universal motors spark a lot during normal operation. Makers of products like inflatable beds have a lot of incentive to keep their costs down as well as the size and bulk, I think the motor on the pump would be one of the main areas they could economize.

The brushes look fine. They look clean at the ends, slightly curved from where they make contact. No signs of any rod. The springs are definitely pushing them in the right direction. The commutator is a dirty copper colour from the graphite debris. The entire armature is able to slide a centimeter or so back and forth. I assume this is normal.

There is more than the usual small sparking. The fact that I smell something burning tells me not to continue.

The excessive arcing may be due to high motor loading. It may be binding somewhere, or the bearings may be shot. Does it turn easily by hand?

Oh absolutely, heat and odor are sure signs of a problem in a motor. As QED suggests it sounds a lot like an overloading problem, possibly a bad bearing.

I intended the sparking comment for Interconnected Series of Tubes, in my limited experience with those types of devices, the motors are set up to operate in forward or reverse (to inflate or deflate) so the brushes aren’t set up exactly in the neutral plane where there is no sparking for one direction because there would be excessive sparking in the reverse direction. They just set them up in a position to get the least sparking they can in either direction.

Yes, it turns very easily by hand. After trying it again, there is a tremendous amount of arching come directly from the brush area. Also, an annoying squeal which leads to believe it is a friction problem. Quite a mystery.

What about whatever it is the motor drives? Does that also rotate freely?

What you’re describing sounds very much like the brush holder has shifted, the entire assembly can be rotated relative to the stator. Armature reaction causes theses exact symptoms in DC motors, I’m not sure about universal motors which is probably what’s in your vacuum. In DC motors we usually just run the motor and shift the brush holder until the arcing is minimized, at least we used to - I haven’t seen a problem like that in a long time. Look at the assembly holding your brushes and see if it could have moved.

The motor drives a fan (its a vacuum cleaner). I always assumed that the fan was turning too but I’ll check it out.