Heavy sparking fr brushes in a vac clnr.

[Andy]

I have a very rugged vacuum cleaner which started to behave strangely the
other day. When running, all of a sudden it just died. A gentle kick made it
run again! This went on for a while and then it started to run very badly,
like a 4 cyl engine running on 2 or 3. A smell of ozone was present as
well...
This convinced me to open it up and it didn't take long to find out that one
of the leads to the filter cap (x+2y) had broken. This was due to the cap
being a bit loose making it vibrate.
It was an easy task to find a new, similar, capacitor and assemble it all.
Then the test run made me disappointed. The motor ran, but badly as before
and the brushes was sparking *heavily*. What could it be?

Any tips or ideas are most welcome!

 

[Sam Goldwasser]

I have a very rugged vacuum cleaner which started to behave strangely the
other day. When running, all of a sudden it just died. A gentle kick made it
run again! This went on for a while and then it started to run very badly,
like a 4 cyl engine running on 2 or 3. A smell of ozone was present as
well...
This convinced me to open it up and it didn't take long to find out that one
of the leads to the filter cap (x+2y) had broken. This was due to the cap
being a bit loose making it vibrate.
It was an easy task to find a new, similar, capacitor and assemble it all.
Then the test run made me disappointed. The motor ran, but badly as before
and the brushes was sparking *heavily*. What could it be?

Any tips or ideas are most welcome!

Are the brushes free to move and firmly against the commutator?

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[Andy]

Are the brushes free to move and firmly against the commutator?

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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Yes, they are free to move and their surfaces look OK.

 

[Tweetldee]

I have a very rugged vacuum cleaner which started to behave strangely the
other day. When running, all of a sudden it just died. A gentle kick made it
run again! This went on for a while and then it started to run very badly,
like a 4 cyl engine running on 2 or 3. A smell of ozone was present as
well...
This convinced me to open it up and it didn't take long to find out that one
of the leads to the filter cap (x+2y) had broken. This was due to the cap
being a bit loose making it vibrate.
It was an easy task to find a new, similar, capacitor and assemble it all.
Then the test run made me disappointed. The motor ran, but badly as before
and the brushes was sparking *heavily*. What could it be?

Any tips or ideas are most welcome!

The commutator segments on the armature of the motor may have been damaged
by the sparking. Disassemble the motor sufficiently so that you can get
access to the brushes and commutator. Get a small piece of emery paper or
emery cloth of about 400 grit and polish the commutator. Hold the emery
firmly against the commutator and rotate the armature so that the copper
segments are polished until they are smooth and shiny.

Make sure that the brushes are not pitted or grooved. If they are, replace
them. You should be able to get replacement brushes at an appliance parts
store.

 

[Sue D Nim]

Never use emery abrasives on non-ferrous metals. Clean up the commutator
with a file to smooth it; and, clean out the area between the segments
carefully with a small scraper. Replace the brushes with new ones. Flush out
any debris w/ electrical motor cleaner, but do not ruin the motor bearings
lubrication.

 

[Sam Goldwasser]

The commutator segments on the armature of the motor may have been damaged
by the sparking. Disassemble the motor sufficiently so that you can get
access to the brushes and commutator. Get a small piece of emery paper or
emery cloth of about 400 grit and polish the commutator. Hold the emery
firmly against the commutator and rotate the armature so that the copper
segments are polished until they are smooth and shiny.

Probably better to use sandpaper - emery is conductive to some degree
and may leave all sorts of conductive stuff in the motor! Of course, so
is graphite so maybe it doesn't matter. You need to get as much of the
dust as possible out in any case.

Make sure that the brushes are not pitted or grooved. If they are, replace
them. You should be able to get replacement brushes at an appliance parts
store.

Just wrap a piece of sandpaper around the commutation and rotate the
armature with some pressure on the brushes. That should form fit them
and remove the damage.

It's also possible that there are shorted turns in the coils which is
the real cause of the sparking.

If the sanding and polishing doesn't help and the brushes seat firmly
against the armature, then electrical problems are likely.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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[mowhoong]

Are the brushes free to move and firmly against the commutator?

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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[Andy]

OK, I will try that. One thing struck me, though. Is it possible that small
grains of copper could be between the segments, thus making a short?
Second: What is the expected resistance of the rotor. 1000 watts @ 230 volts
should yield 53 ohms, but I guess that AC makes things
complicated...XL=jwL...

 

[Sam Goldwasser]

OK, I will try that. One thing struck me, though. Is it possible that small
grains of copper could be between the segments, thus making a short?
Second: What is the expected resistance of the rotor. 1000 watts @ 230 volts
should yield 53 ohms, but I guess that AC makes things
complicated...XL=jwL...

Yes indeed. As someone else suggested, clean the communatator including
between segments.

And yes indeed, AC does change things. What you can check is that the
resistance between segments on opposite sides of the commutator should
be about the same for all (well, 1/2) the segments.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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[Andy]

Damn, this thing makes me crazy! I have measured all the windings. 0.2 ohms
between to neighboring segments yielding a total of ca 2 ohms between
opposite segments. Everything seems to be in order, and still, the brushes
spark more than the sky on New Years Eve...

 

[Jim Adney]

Damn, this thing makes me crazy! I have measured all the windings. 0.2 ohms
between to neighboring segments yielding a total of ca 2 ohms between
opposite segments. Everything seems to be in order, and still, the brushes
spark more than the sky on New Years Eve...

A commutator that is rough, or out of round, will also cause sparking.

I don't know, but if it is a series wound motor with shorts in the
field winding, then it would draw excessive current thru the brushes
which could also cause sparking even if there was nothing wrong with
the commutator or the brushes.

-

 

[Rheilly Phoull]

Damn, this thing makes me crazy! I have measured all the windings. 0.2 ohms
between to neighboring segments yielding a total of ca 2 ohms between
opposite segments. Everything seems to be in order, and still, the brushes
spark more than the sky on New Years Eve...

The conventional test is to put the armature on a 'growler' and test for
shorts and opens, however if the sparkes are 'heavy' and strong there would
be shorts in it, open circuit windings give long trailing sparkes around the
commy and also the edges of the open circuit comm bars will be burnt. Since
you have tested for continuity I would guess there are shorts, they are hard
to find with a VOM.

 

[H. R. Bob Hofmann]

Damn, this thing makes me crazy! I have measured all the windings. 0.2 ohms
between to neighboring segments yielding a total of ca 2 ohms between
opposite segments. Everything seems to be in order, and still, the brushes
spark more than the sky on New Years Eve...

What everybody has overlooked is that a single shorted turn on any one
of the commutator coils is not going to lower the apparent resistance
of that coil enough to be detectable, but it will kill the inductance
of that coil and cause fireworks as described by the poster. If
anyone has an extra motor, just try it and see.

H. R. (Bob) Hofmann

 

[Andy]

I noticed that the new x-y filter is configured as 2 x 4700pF + 0.10uF
whereas the old was 2 x 4700pF + 0.15uF. I assume that this gizmo is only
there to reduce RFI but could the lower capacitance cause the sparking as
well?

Thanks for all your contributions on this neverending story!

 

[James Sweet]

What everybody has overlooked is that a single shorted turn on any one
of the commutator coils is not going to lower the apparent resistance
of that coil enough to be detectable, but it will kill the inductance
of that coil and cause fireworks as described by the poster. If
anyone has an extra motor, just try it and see.

H. R. (Bob) Hofmann

An ESR meter or flyback transformer tester should work to test for shorted
turns.