Arcing brushes hoover motor.

Any ideas what's a matter with my poorly motor.




2kW universal motor, burning the bejaysus outtov her brushes. I can see the blue sparks bouncing from inside the 2mm matt red plastic shrouding.
Smells like an angle grinder chewing stainless steel.

It's a switch - parallel indicator light- series NC thermoswitch - parallel non polarised polyester capacitor - universal motor.

Bypassed the thermo switch, swapped the capacitor, cleaned the commutator, ground the brushes smooth and seated (loadsa meat on 'em). As far as I can tell there's no shorted rotor windings..they're all about 3.5Ω
Not much else to it, dunno if there's much in the way of filtering or passives I can't get to the back of the switch or incoming flex gland without a torx with a 8 inch drive :rolleyes:.

I've 0 current on the motor incoming live before the brush box read by a clamp meter and meter with a 1000V limit is showing voltage out of limit at the brushes.
Voltage at the socket drops 5V with the motor spinning up.

-125mbar pressure switch parallel with the motor circuit.



Thoughts?

Bruthal

The usual causes are possibly contamination between the commutator strips. The insulating slots between copper should be below the level of the copper strips.

Shorted section of winding is another, although you seemed to have ruled that out.

Possible brush sticking in guides, or weak springs, meaning the brushes not making good contact.

Worn motor shaft bearings might be another possible cause.

Thanks Bruthal,

I gave up and chunked it in the scrap bin with a box of alternators with failed rectifiers. If I get really bored one day I may resurrect it and have a go at making an inverter from the lot.

Residual magnetism aside I'd a fairly even reading of resistance from brush to brush rotating slowly by hand. It looked like one of the brushes was catching a commutator slide and possibly skipping when it was running.
Could be krudd in the commutator too...never thought to check.
No way to swap the brush springs but there was an inch and a half of brush in the box so unlikely.
Bearings were fine, axis looked true.

I ground the commutator with sandpaper on the back of a prybar while turning it on a drill. Then left the drill on it for an hour to seat the brushes again. No joy.

There was nothing behind the switch or at the cable entry point.

I told SWMBO to get a new motor in the end. 2kW vacuums may be banned from sale in EU but the motors are still available...and a fairly standard size too.

Bruthal

I had the same thing happening with a drill recently. I could feel particles of the brushes coming out through the vents. Brushes worn down seems to be the cause although I have not put new ones into it yet.

Higher loadings on universal motors can make it worse. With vacuum cleaners though, its at its highest when they have clean filters and unobstructed hose. Load on motor actually reduces as the hose or filters become obstructed, and the motor rpm increases as a result. So they don't really get overloaded in electrical terms.

It might have been interesting to try bedding in the newly ground brushes by running the motor.

Sanding the commutator may have left it slightly rough. They need to be polished, running the brushes in may have done that after the sanding too. Its an interesting one anyway.

Bruthal

1000 Grit.

Fair point, I had it turning no load.

Bruthal wrote: »

It might have been interesting to try bedding in the newly ground brushes by running the motor.

I did run the motor except with a drill. See the attached mini lighting storm when I tried it under her own steam.