Changing carbon brushes on a Dyson DC19 vacuum cleaner. Good idea?

내 문제

Under normal use this ~10 year old vacuum cleaner with YDK motor, suddenly made an unusual sound and smoke suddenly started to pour out before it switched itself off.

The 'post motor filter' was full of black crumbly carbon and being hot it melted the plastic (HEPA?) filter (bad smell). Taking the motor out showed that the carbon brushes had failed. (A 'Vacuumspot' video on YouTube showed how to dismantle a DC19 vacuum cleaner.) The carbon brushes were not just worn down (from 33mm to 7 and 11mm) but seriously damaged.

나의 수리

I bought some new Qualtex brushes (7x11x33mm £3.50 eBay) and soldered them into the brush holders (you can buy them ready assembled in their holders for about twice the price.)

After I reassembled everything and turned on, the vacuum cleaner spat out the new brushes with lots of smoke after a few seconds. The new brushes had reduced from 33mm to 23mm in seconds.I was confident that I had done nothing wrong. (I've changed brushes a few times).

So I put in a new motor (£19.45 eBay) and new filters (£6 eBay) and the vacuum cleaner worked well again.

내 조언

Normally, carbon brushes need changing when they wear out so much that they no longer contact the commutator, so no current passes to the rotor and the motor stops or sparks a little.

The windings had good consistent resistances, the motor looked visually good, the 220uF capacitor read 95uF (bit low but probably not the major fault) and the commutator was round to within 15 microns. Both bearings (extracted) however exhibited some slight play, and I'm guessing that the rotor went into resonance which would explain the sudden failure.

So the advice is perhaps: change brushes when they are worn out, but not when they are seriously damaged.