Carbon brush question.
 

I have a B&D electric drill and the carbon brushes are sparking
excessively. (I'd expect a *little* sparking but this is a lot) Apart
from that the drill runs fine.

Inspecting the brushes there is about 1/4 the original length left and
the nds are rough, so they need replacement.

However, will replacing the brushes/cleaning the commutator cure the
sparking?

If not, what else could be causing the sparking?

S

--s-p-o-n-i-x-- wrote:
I have a B&D electric drill and the carbon brushes are sparking
excessively. (I'd expect a *little* sparking but this is a lot) Apart
from that the drill runs fine.

Inspecting the brushes there is about 1/4 the original length left
and
the nds are rough, so they need replacement.

However, will replacing the brushes/cleaning the commutator cure the
sparking?

If not, what else could be causing the sparking?

S

in 9/10 cases yes

NT

--s-p-o-n-i-x-- wrote:

I have a B&D electric drill and the carbon brushes are sparking
excessively. (I'd expect a *little* sparking but this is a lot) Apart
from that the drill runs fine.

Inspecting the brushes there is about 1/4 the original length left and
the nds are rough, so they need replacement.

However, will replacing the brushes/cleaning the commutator cure the
sparking?

If not, what else could be causing the sparking?


Yes it will.

Excessive sparking is bad contact which is worn brushes and/or weak springs.


Its hioghly unlikley the commutator will be worn.

Go easy on teh power till the new brushes bed in.

S

Put the armature in a heavy drill and spin it up and polish the
commutator with very good carborundem paper. Clean out the insulator
groves again and put it all back together. The commutators should be in
immaculate condition for the brushes to properly transfer power. You
may still get some sparking but it should soon settle down.

"--s-p-o-n-i-x--" wrote in message
...
I have a B&D electric drill and the carbon brushes are sparking
excessively. (I'd expect a *little* sparking but this is a lot) Apart
from that the drill runs fine.

Inspecting the brushes there is about 1/4 the original length left and
the nds are rough, so they need replacement.

However, will replacing the brushes/cleaning the commutator cure the
sparking?

If not, what else could be causing the sparking?

If the sparking has got slowly worse, changing the brushes and cleaning
the commutator will probably be all that's needed.

Severe sparking that starts suddenly, accompanied by some loss of power
(not always very obvious), and an occasional refusal to start unless the
chuck is turned slightly, indicates a fault with one or more armature
windings, either in the winding itself or its connection to the
commutator.


--
Kevin Poole (ex production liaison engineer, B&D, only 30 years ago)
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

Thanks all!

ANyone know where the best place is to get brushes?

sponix

--s-p-o-n-i-x-- brought next idea :
I have a B&D electric drill and the carbon brushes are sparking
excessively. (I'd expect a *little* sparking but this is a lot) Apart
from that the drill runs fine.

Inspecting the brushes there is about 1/4 the original length left and
the nds are rough, so they need replacement.

However, will replacing the brushes/cleaning the commutator cure the
sparking?

If not, what else could be causing the sparking?

The sparking could also be due to shorting between the commutator
segments, shorted turns in the windings, or simply poor spring
pressure. Once it starts it will only get progressively worse. Assuming
there are no other problems with the motor, such as shorted turns in
the winding or a badly damaged commutator....

As someone else suggested, it would be worth while cleaning up the
commutator first by spinning it in another drill and using very fine
glass paper to clean it up and polish it at the same time checking that
none of them are loose. This will take care of light damage.

Each segment is supposed to be insulated from the next and the gap
between them can fill up with conductive carbon from the brushes. It
would also be wise to undercut them after polishing up the commutator.
The usual method is to carefully grind down the thickness of an hacksaw
blade to fit the gap, then draw the blade down the gap working away
from the winding end towards the end of the shaft, being careful not to
scratch the copper faces or loosen any segments by twisting the blade.
Then just give it a final polish to remove any slight burrs.

If the brushes are not rounded at the end to suit the commutator, wind
a single layer of glass paper round the commutator, assemble, fit the
brushes loosely in their holders and turn the shaft to bed them in
against the paper.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

--s-p-o-n-i-x-- laid this down on his screen :
Thanks all!

ANyone know where the best place is to get brushes?

sponix

Cheapest would be to try to match them against the stock items carried
by an electrical specialist, failing that B&D can supply them.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

Hi,

Having repaired power tools for many years, it is probably not the
brushes - it is far far more likely that the drill is burnt out
(insulation between the windings has broken down due to excessive heat)
It takes a lot of use to wear brushes down but it does happen.

If you need to compress the springs to get the brushes into place then
it isn't the brushes.

That said, brushes are pretty cheap and worth a try. You should be able
to get them from your local friendly power tool sales/repair place. In
fact, if you took it in to them they should be able to tell you within
2 seconds of plugging it in what the problem is.

A dirty commutator is also possible but unlikely. Cleaning it with a
little light emery paper and gently cleaning out between the segments
is an easy task.

It could also be sticky brushes where crud prevents the brush from
moving freely in its holder and therefore from properly touching the
commutator - do the brushes move in and out freely? If not, clean them
and the holders.

Let us know how you get on.
(my fingers are crossed for you that it is something cheap)

Alan.

In article . com,
Alan wrote:
A dirty commutator is also possible but unlikely. Cleaning it with a
little light emery paper and gently cleaning out between the segments
is an easy task.

My 'book' says never to clean commutators with emery as particles can
embed themselves in the copper. Glass paper is said to be the definitive.
Personally, I use wet or dry.

--
*Nostalgia isn't what is used to be.

Dave Plowman London SW
To e-mail, change noise into sound.

On 18 Apr 2005 09:16:45 -0700, "Alan"
wrote:

Hi,

Having repaired power tools for many years, it is probably not the
brushes - it is far far more likely that the drill is burnt out
(insulation between the windings has broken down due to excessive heat)
It takes a lot of use to wear brushes down but it does happen.

Well, there's probaby 1/4 of the original brush length left.

If you need to compress the springs to get the brushes into place then
it isn't the brushes.

Yes, they do need compressing although the pressure isn't very much.

That said, brushes are pretty cheap and worth a try. You should be able
to get them from your local friendly power tool sales/repair place. In
fact, if you took it in to them they should be able to tell you within
2 seconds of plugging it in what the problem is.

I'm going to measure the resistance of the windings. What sort of
resistance should I expect between opposite commutator segments?

On Tue, 19 Apr 2005 07:58:45 GMT, (s--p--o--n--i--x)
wrote:

I'm going to measure the resistance of the windings. What sort of
resistance should I expect between opposite commutator segments?

Lower resistance than you can probably measure accurately, unless you
rig up something like a 4-wire meter. Look for consistency of
resistance between paths, or gross open circuits
--
Cats have nine lives, which is why they rarely post to Usenet.

I agree with Andy - less than you can measure accurately. I've never
had to measure winding resistance in a small motor as I can always tell
what is wrong with it just by running it.

If your drill is burnt out, you will be able to see signs of
overheating on the windings. No need to measure anything.

By the fact that there is still some compression in the springs, I
think the brushes are probably not the problem. I have in the past put
a little piece of something between the spring and the brush just to
make sure just for a quick test. You could do the same - just make sure
the "something" can't fall into the motor housing and damage it.

Another thought - do your brushes have wires on them to connect them
electrically or do they just rely on the contact between brush and
holder?. If the former then I have seen the wire being too short or
caught round the back of the holder and thus preventing the brush
making good contact while still having plenty brush length. Again,
unlikely but something to check.

And Dave - interesting what you say about emery. I've never heard that.

On 19 Apr 2005 04:26:53 -0700, "Alan" wrote:

If your drill is burnt out, you will be able to see signs of
overheating on the windings. No need to measure anything.

The best way to test them is by use of a "growler", which detects
shorted turns (or turns shorted to the armature). These are hard to
find, but I did notice one on eBay a few days ago.