"Andrew Gabriel" wrote in message
...
Whilst visiting parents, I got called upon to investigate vacuum cleaner.
Apparently, whilst being used, the motor started slowing down and giving
off a burning smell. I was expecting a motor brush to have worn out, but
on investigating, the brushes were fine. The commutator was a bit dirty,
which I cleaned up with some fine sand paper, but there was nothing else
obviously wrong with the motor. When I had the brushes out, the armature
spun very freely in its bearings. Having reassembled it, I ran it for a
few minutes without the brush bar belt, and the drive shaft had got hot
enough to burn me, although the motor didn't slow down, so I'm not sure
if I changed things by cleaning the commutator. Connected back the brush
bar and used it for a few minutes -- smell of hot electrics, although it
seemed to be working. I had also cleaned the internal filters, but they
weren't heavily clogged, and the bag was only a 1/3rd full.

Any suggestions what might be wrong with it?
If it's a gonner, would be good to get a new one while the sales are on.

Andrew Gabriel


This may have been caused by dirt in the carbon brush holder. If it gets to
dirty in there it can cause the brush to stick and not to make full contact
with the armature. This causes an arc to form across between them like a
welders rod. It also explains the smell of electrical burning and the motor
slowing.

If the carbon brush has been allowed to arc for a while it begins to heat
the sections on the armature and can damage them to the point of causing a
failure on the armature due to the enamel coating on the coil wire being
burned off and a short forming across the windings.

The damage caused by an arcing carbon brush may also be the cause of the
over heating you're getting on the vacuum motor now. The enamel itself may
be at the point of causing a lower resistance path between the armature
windings, but not quite at the point of causing a direct short that would
probably blow a fuse or cause the motor to stop.

Look at the coil wires on the armature where they meet the brush sections.
If the enamel looks to be discoloured, usually a darker brown than the rest
of the windings, then the armature will need replaced. You might also see
burning marks or lifting off (loosening) on the actual brush sections if
they've been allowed to heat to long without remedial work.