garden vac/shredder sparking and smoking

happyhero

Hi I have a Black&Decker garden vac/shredder and I think I have had it for two or three years. Recently I heard it change sound so I had a look and found the brushes right at their limits.

I am a retired electrician so I know what I am doing by the way. Anyway I went and got some new brushes and fitted them. It seemed to work fine and sounded as it it used to, just noisy not noisy and horrible, but after about 15 minutes use I smelt burning. I let it cool and tried again and the same thing happened. Now I know I put the brushes in correctly and there is only one way they can go in anyway. And I know sometimes brushes take a little while to bed in but this is different. Something is not right.

When you look inside I can see an abnormaly large quantity of sparks where the brushes touch and also when you switch it off you get a small whisp of smoke coming out.

I know it looks like I did something wrong with the brushes but I am confident that I fitted them correctly so any other ideas what could be causing the problem, ie something braking down, not that there is that much inside. I am quite happy to repair and replace a few cheap parts to get it working correctly. I am hoping someone on here has come across this problem before and will be able to tell me exactly what the problem is.

Any help appreciated.

catkins

Did you clean the rotor and make sure the gap in the segments was clean?

happyhero

catkins wrote:

Did you clean the rotor and make sure the gap in the segments was clean?

No I didn't but it did not look that worn at all and I did not notice any muck between the segments. I am going to take it apart again and see what may be the cause, so I will check more thoroughly inbetween the segments this time. To be honest I hope I do find something, at least I can fix it then.

gromituk

Shorted turn in rotor or stator windings?

happyhero

gromituk wrote:

Shorted turn in rotor or stator windings?

If that is whats wrong, then are you saying it would still work but just cause this sparking?

Could it not be anything else causing it?

gromituk

I would think so with a shorted turn in the armature yes - I expect that winding will just take a great deal of current. As for the stator, well I suppose a shorted turn might stop it rotating completely.

gromituk

There's not much else to go wrong really - if the bearings and brushes are OK.

happyhero

I am right in thinking that you should never get smoke when new brushes are just bedding in arn't I and so there is something wrong?

moonrakerz

My first guess would be have you got the right brushes ?

If you can get to do it, put some fine emery cloth on the rotating surface under the brushes and rock the commutator back and forth to shape the contact surface of the brushes to the curve of the comm.

Once you've done that, clean the commutator with a clean cotton cloth held onto the rotating surface with a piece of wood.