Washing machine - brushes replaced, motor is smoking...
GetArmy
WM is a Bosch, 5 years old, average family use.
Recently is has been making a 'ticking' noise when the motor is under
load (which I now know to be arcing) and has caused the circuit
breaker to trip a couple of times.
More recently, the motor stopped working in the middle of a cycle. A
friend who knows a little about these things said that if striking the
motor with the rubber end of a hammer causes the motor to spring back
into life then the fault is most likely with the carbon brushes.
I tried this and the motor did come to life. This happened fairly
predictably over the next few cycles... motor dies ... give it a knock
... complete the cycle. Watching the machine running (with the back
off) I could observe the reflection of the arcing on the WMs metal
floor.
I ordered new carbon brushes from ebay. Not genuine bosche ones (£24)
but compatibles (£8).
I fitted them last night. Sure enough, the old brushes were worn
right down. I put the machine on to do a wash. I immediately noticed
that the arcing was still present. I also noticed that the motor was
generating an electrical smell and soon spotted wisps of smoke coming
from the motor casing.
I immediately stopped the cycle and checked the brushes to make sure
that I had installed them properly. They were in correctly. I
noticed that one of them was hotter than the other. The cooler of the
two was also not moving as freely as the hotter one. There was a
slight protrusion in the brush holder which prevented the brush from
sliding smoothly. The protrusion had rubbed a groove in the edge of
the brush so I 'enhanced' the groove with my screwdriver and it now
slides smoothly.
I also checked out the copper strips on the spindle that the brushes
make contact with. This looks quite worn. Actually I'm not sure if
it's worn or just dirty. There is a definite line of wear around the
strips which looks like it could have been caused by the end of the
braid/wire which was visible on the end of the worn brushes. I gave
the copper strips a wipe with kitchen towel and a little carbon powder
came off them but mot much. The gaps in between the copper strips
didn't look to be particularly full of carbon dust.
I reassembled everything and allowed the washer to do another cycle.
The motor was still smoking gently throughout all parts of the cycle.
Perhaps less so on the spin but that may be just the increased air
movement dispersing the smoke. I think that the arcing may have been
getting a little less but not so, the smoking.
Is this normal for a new set of brushes? Although the old ones were
completely worn out and arcing, they never caused any smoke or a
smell. I'd rather avoid having to pay £128 for a new motor if
possible!
Any ideas?
Thanks
Mike
Bruce
Perhaps the Bosch brand brushes would bed in more quickly? Unless you
are sure that the £8 branded brushes are exactly equivalent to the £24
Bosch brushes, I think I would probably have spent the £24 to save the
£128, rather than taking a risk on the £8 unbranded set.
The brushes will have had square ends and you will need to give them
time to bed in and take the shape of the commutator. Until that time
there probably will be some arcing, but it will reduce as they bed in.
I replaced the brushes on a Hoover washer and they took about 10-15
washes before they fully bedded in.
Harry Bloomfield
Brushes really need to be either pre-formed to shape at the face, or
shaped by hand. Usual way is to wrap a strip of fine sand paper around
the commutator and push the brush against this as you spin the
commutator. Brushes should always be refitted in exactly the same
orientation to the commutator as when removed. Carbon dust in the
caught in the commutator gaps can short out and cause damage to the
commutator - always clean it out.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
meow...@care2.com
Carbon between the comm segments might possibly be the cause
of the excess current/heating/smoke, but I'm certainly not saying it
is, there are other possibles. Easy place to start though.
NT
meow...@care2.com
Motor overcurrent is also caused by partial winding shorts
(damaged insulation), for which the only solution is a new motor or
rewind.
Some WMs arent worth putting a new motor in. When that happens
its possible to keep a damaged one running long term by fitting a
series impedance. Its a bodge, but works, and is a useful option for
people on benefits etc. It reduces spin speed a bit. If thats an
attractice option, you should test it only using an impedance, as
any further smoking will quickly and heavily worsen it, quite likely
killing it.
NT