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
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.
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.
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.
Thanks all!
ANyone know where the best place is to get brushes?
sponix
--s-p-o-n-i-x-- brought next idea :
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.
--s-p-o-n-i-x-- laid this down on his screen :
Cheapest would be to try to match them against the stock items carried by an electrical specialist, failing that B&D can supply them.
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.
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.
Well, there's probaby 1/4 of the original brush length left.
Yes, they do need compressing although the pressure isn't very much.
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
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.
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.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.