Brushes in an universal motor: opinion on their condition

[golden_labels]

I’m a newbie regarding electric motors. Worn out brushes I’ve seen previously were usually much shorter.⁽¹⁾ Would you consider these to be still fine?

These come from an universal motor from a cheap paper shredder. Fixing it is likely not financially reasonable, but I won’t mind learning something.

Also: yes, they were mounted perpendicular to their original profile.

⁽¹⁾ I’ve just realized I forgot to take photos showing the brushes’ size. They are 4×5 mm, currently 10 mm in length. Certainly still pushing well against the commutator.

[johansen]

Whats the problem?

[Jeff eelcr]

Most pictures look strangely worn, 1 looks normal.
Jeff

[perieanuo]

change them, pressure and shape taking rotor shape is the key

[wraper]

Looks weird, as if brushes were misaligned with commutator and one side has no wear at all, the same as 2/3 of commutator.  Does the brush size match the slot size properly? And are the brush slots located correctly above the commutator?

[golden_labels]

Whats the problem?

The distal issue is overheating.

Brushes are something I just noticed while cleaning the entire drive assembly. I don’t have any strong motivation to replace them: the entire shredder costed $20 when new. But I don’t mind learning something about evaluating the state of the brushes. All I have seen in my life lost most of their length, had obvious cracks etc. These here seem just weird.

Most pictures look strangely worn, 1 looks normal.

The collage is a close-up, each photo about 5–6 mm in width. Perhaps the magnification make it look unfamiliar. The first picture is a general view of brushes and the commutator.

Looks weird, as if brushes were misaligned with commutator and one side has no wear at all, the same as 2/3 of commutator.  Does the brush size match the slot size properly? And are the brush slots located correctly above the commutator?

The brushes look as if they were originally profiled to work with a completely different configuration. The wedged surface seems to be cut like that. It is mostly not touched. The commutator touches the brushes along the wider axis, at the tip. You can see a dip in that direction on the first, bigger photo.



I see nothing wrong with slots.

[coromonadalix]

or the rotor is not centred on the brush surface ??

anyway  its not normal,  to have wear in non uniform fashion ?

[wraper]

The brushes look as if they were originally profiled to work with a completely different configuration. The wedged surface seems to be cut like that. It is mostly not touched. The commutator touches the brushes along the wider axis, at the tip. You can see a dip in that direction on the first, bigger photo.

Then it's weird but brushes are barely worn. With more wear there will be full commutator coverage. IMHO leave it as is.

[BrokenYugo]

Small cheap paper shredders are just prone to overheating in my experience, and the page ratings must be assuming something like newspaper, run it at half capacity max. If it takes at least a few batches of a few sheets in a row to trip the thermal overload and doesn't let the smoke out it's probably working correctly.

[golden_labels]

Thank you all for confirming, that it’s not only my inexperience and there is something weird with those brushes.

The wedged side of a brush is aligned with rotor’s axis:


As for overheating (the original issue) of cheap shredders: it wasn’t doing this before. Now it’s failing to shred 2 sheets, inserted separately.  Mother asked me to check it. It has some years, grease is everywhere but on the gears, a few pieces of paper mixed with grease stuck in gears and inside the motor. Before throwing it away I decided to clean and regrease the drive and blades. I found those weird brushes inside and considered that an opportunity to educate myself more.

For the record: Tracer TRANIS40566.

[wraper]

I guess it's some oddball version of this that allows brush wearing the shape of commutator faster. Nice drawings BTW.