240V Drill .. One Brush Worn Right Down

[aesmith]

This is an Elu SDS masonry drill, not sure how old but it dates from the time they were changing to Dewalt branding for everything.

It stopped working, then next time I tried it worked then stopped and stayed stopped.

One brush was worn right down, but the other looks virtually full length. I didn't even replace that one as I wanted to check it worked with the worn one replaced. It does. Now I'm wondering why one would wear and not the other. This is new to me, I've actually never before had to replace brushes in any power tool, and I wouldn't say that drill has had more use than other tools of the same age.

Could a fault somewhere else have caused this?

 

[Nomad]

Check the brush moves freely in the brush holder.

I’ve had similar (brushes different length) before when one holder was slightly deformed causing the brushes to stick.

 

[aesmith]

Cheers. I think I'll have it apart again to check that. It sparks quite a lot, i guess that could be poor contact.

 

[aesmith]

Seems free, but of course it might have been sticking in the past. For your viewing pleasure. From left to right, worn top brush, existing bottom brush and finally new brush.

 

[Smallfry]

Not unusual. Happens with alternators too. No idea why though.

 

[Dapph2]

Check for cleanliness in the carrier and freely sliding in the carrier . I've had to rub down new brushes in fairly newish Bosh drills .


You can also get abrasive dust in the carrier which will stop the affected brush moving , so it will arc & burn out on the sticking brush

 

[Erie Fred]

and with all that brush wear, just where did the carbon go to ?

Time to use a air hose to blow out the motor, concentrate on the spaces between
the copper commutator bars as well.

 

[aesmith]

Cheers, another good point.

 

[Dapph2]

and with all that brush wear, just where did the carbon go to ?

Time to use a air hose to blow out the motor, concentrate on the spaces between
the copper commutator bars as well.

Usually when I change brushes along with cleaning I grind a square edged hook into a hacksaw blade at the eye end and hook/scrape the crap out from between the commutator segments . If you don't do that you are likely to get arcing between the segments due to carbon build up.

I also bed the brushes in to the armature using a very fine shark skin paper to get them to fit bed into the circumference of the commutator ..