Can someone explain how a brush DC motor wears out?

[sugarwood]

Replaced my blower motor and was curious how these fail.

How do the brushes wear out?
Do they always make light contact and eventually sand themselves down?
There were a lot of magnetic shavings in the casing.

[DRACO A5OG]

Yes, it always makes contact and it is a wear item.

Check the voltage regulator, it too has 2 brushes that wear.

[sugarwood]

But, why doesn't the brush wear out almost instantly then?
If it's rubbing, you'd think a few mins. of rotation would grind it away, and no more connection!

Ok, at 2:34 it says the commutator brushes are spring loaded.
Now I get it. The brush is like a brake pad.
https://www.youtube.com/watch?v=LAtPHANEfQo



In my photos below, on the left side, you can see the brush housing was simply cracked off
(so the brush is not even touching the commutator anymore)
That explains the random spring just sitting in the housing.
The upper right is the intact brush which still touching the commutator correctly.

[sugarwood]

So, when someone repairs a DC motor, what are some common failures?
Cleaning the commutator?
Replacing the worn down brush by splicing in a new one?

[dad911]

I find the bearings/bushings fail often. Check for play or tightness in shaft.

Spring isn't a brake, it keeps the brushes in contact with the armature, as the brushes wear.

[atcjorg]

the brushes in that motor are worn out and about to fail, i think 1 has already, you can clean the commutator with a soft pencil eraser, spray with electronics cleaner, do not nick any of the windings, with the brushes removed the bearings should turn freely but not wobble (run out)

[sugarwood]

Originally Posted by atcjorg

the brushes in that motor are worn out and about to fail, i think 1 has already, you can clean the commutator with a soft pencil eraser, spray with electronics cleaner, do not nick any of the windings, with the brushes removed the bearings should turn freely but not wobble (run out)

I already replaced the motor.
It was smoking and then died.
You can see it's fried.

[Quicksilver]

Originally Posted by sugarwood

But, why doesn't the brush wear out almost instantly then?
If it's rubbing, you'd think a few mins. of rotation would grind it away, and no more connection!

. . .

The brushes are made of graphite which is also used as a lubricant.

-----------------------
The obvious wear items in an electric motor are the brushes and the bearings. A less obvious point of wear is the windings. The windings are usually insulated with a thin varnish like coating and to ensure long life they are coated with what is called potting usually made of epoxy.
As the magnetic fields build and fall during the rotation of the motor it will cause the wires to tend to move a minute quantity. Now matter how small the movement it will cause the wires to rub against each other. Over time this will allow the insulating coating to wear out causing shorts. The windings are coated in potting to hold them rigidly together so the windings can't wear out. A sign of a cheap electric motor is an incomplete job of encasing the windings with potting.

[grant lyon]

Brushes are the usual wear item that causes loss of function. If you still have one of the two motors with good brush holders, you can just replace the brushes. The carbon brushes wear slowly because they are dryfilm lubricated by the carbon riding on copper commutator segments -- think of writing with a pencil not on paper (a relatively rough surface) but on glass -- slides easily. I would cut the braided lead to one of the brushes in half, fish the brush out and measure the height x width dimensions and estimate length from the holder and look for brushes on the web. If you can get the braid out of the crimp connection on the board then you crimp the lead of a new brush there -- otherwise you may be able to just cut the new braid to length and solder to the bit of lead hanging out of the crimp connection. Minimum solder because you want the flex braid to be able flexible to allow the brush to move freely in the holder channel. If you're not adventurous, you might just take the motor to an old fashioned sewing machine vacuum repair shop -- you want the old hole in wall in business since WWII type and they may be able to make the repair, or if nothing else supply you with brushes that will work. (BTDT, for replacement brushes.) In the pict where you show the loose spring you can see the bearing in the bottom the housing and it looks like a simple sleeve (not ball) bearing. See if you can rotate that innermost silver cylinder to determine if this is just a sleeve bearing. Oil sparingly (w light machine oil, e.g. 3 in 1, Triflow) either the sleeve or the ball bearing on both ends of the motor shaft to get a freely rotating assy. Sparingly because you don't want to gum up the commutator. On the motor commutation segments you want clean smooth surfaces, but you want to avoid getting any debris between the segments (the slots) because this can cause shorting and malfunction of the commutation. If IPA or light solvent doesn't get the crud off the commutation segments (an eraser is a great idea too, 1st choice), you can try very very fine, say 2000 grit polishing paper to clean taking care to move the paper parallel to the segments to avoid loading the slots between the segment with debris. Need to clean the slots between the commutation segments thoroughly but take care not to be so aggressive as to damage the motor insulation. My guess is the brush holder turns on the rivet connection to the board, and that is way you can load the new brush (with spring in the holder 1st) into the brush holder. If the brush, pushed back into the holder is too long you can just file off some of the excess length. Haven't repaired this specific motor (engine cmpt hot air blower? doesn't look like fresh air blower motor) so I may be off on some details but HTH

[sugarwood]

Thanks, but I am not going to repair this.
Well, maybe I'll play around with it, but I've already replaced it anyway.

If you look at the very first photo I posted, the brush housing seems to have broken off.

Also, the motor, once separated, doesn't really seem to go back together correctly anymore.

[sugarwood]

Look, here are replacements. Good to know something new.
4 Pcs DC Electric Motor 1/5" x 1/5" x 15/32" Carbon Brushes | eBay

[Driven97]

Oh wow neat. In your first photo, looking at the brush housing, see the relief at the top for the wire? When new, the brush length was such that the wire came out the the outermost portion of that relief. Took 30 years to wear all that away, so not bad.

The industry is just now slowing converting over to brushless motors in some spots, where electronics controls switch coils off and on to run the motor.

[sugarwood]

The "relief" is the channel for the wire, right?
Yea, what was a long block is now a cube!

If you look at the other one (in the upper right of the triple photo)
you can see a LOT of spring, so that brush is almost all gone also.

I bet the brush was so worn that is finally slipped out of the housing, got caught up,
and ripped the housing right off

[sugarwood]

Look how black the coils are. They seem burnt.