Today I am working on a paper shredder that someone discarded.

All the gearing is intact, and it has a self re-setting thermal fuse, and it is in good shape.

The armature looked real dirty, so I cleaned it with a wire brush, and the unit worked after that.

However, the armature is getting very dirty again, in just 30 seconds of run time.

Does that mean that the brushes are bad?

I've never seen an armature get dirty so fast.

Thanks,
Gary

 

Maybe I figured it out.
One of the brushes has broken loose from the wire that connects it.
The spring is apparently not a good enough conductor, by itself.

The brushes themselves look to be in great condition.

I'll try to resolder the wire to the washer, and see what happens

Edit,
I found an intact one of exactly the same size in my scrap parts bin.
I installed it, and now it's working, but the armature seems to be getting pretty hot.
Perhaps that is what's causing the armature to get dirty so fast?

Any thoughts on that?

Would a bad bearing cause that also?
Thanks

 

If the armature had a shorted winding it might cause the operating current to be abnormally high.
Can you measure its current?

 

I'll check that out, possibly tomorrow if I have time.
Thanks for the input.

 

When I cleaned up the brushes, I filed them flat, where they contact the armature.

I now think that this will impeded performance.
Is there any information about that, that I could read up on?

Any ideas on how long I would have to run the motor (in short burst) to have the armature re-curve the brushes?

I haven't measured the current yet.

Thanks,

Thanks,
Gary

 

When I cleaned up the brushes, I filed them flat, where they contact the armature.

I now think that this will impeded performance.
Is there any information about that, that I could read up on?

Any ideas on how long I would have to run the motor (in short burst) to have the armature re-curve the brushes?

I haven't measured the current yet.

Thanks,

Thanks,
Gary

Check these out
http://www.hobbytalk.com/bbs1/showthread.php?t=126994
http://www.rccartips.com/rc-electric-motor-tuning-guide.htm
Also remember these are DC motors and not sure if the paper shredder is DC or AC motor..

 

I assume this a Universal motor, or is it DC?
The brushes on these are relatively soft compared to their DC shunt lower rpm counterparts.
Normally brushes are bedded to the shape of the commutator, this is done with something called a com stone, a search on this should provide something.
You should not use emery or similar abrasives on a com.
Max.

 

Excellent feedback guys. I've learned something today.
I particularly like the LYSOL Basin Tub and Tile Cleaner tip.

It's a lot more complex than I imagined, but then again, I am tring to get a paper shredder running, not an RC race car.
Those guys are serious............. maybe NASCAR should give that site a look.

Anyway, I'll price a com stone, and take your advice on abrasives as well.

I've been known to use a file, or wire brush attached to a drill motor.
Not a very good practice apparently.

Thanks again,
Gary

 

Is this a $1500 commercial unit or a $10.00 WallMart?
Max.

 

nice information
thanks all

 

It's a Royal, double cross cut.
Probably in the $40.00 to $50.00 range.

When researching the com stone you mentioned, I emailed an outfit in California, and right away, the guy emailed me back, and said that the brushes would probably wear themselves back into the contoured shape, but that the commutator might need to be cleaned up with an appropraite stone. He gave me some things to look for, to select the right stone, but they are saved on my PC at home.

 

Do you see excessive sparking from the brush contacts

 

Yes,
Excessive sparking was seen at start up, but seemed to die down some, after running it for 30 seconds on, then 2 minutes off, a few times.

But I would say it still has excessive sparking.

 

If this is a Universal motor, which i assume it is? Then high sparking level on the com is normal. Especially as load changes.
Max.

 

Thanks for letting me know.

That could save me some unnecessary troubleshooting.

I thought the sparking was abnormal.

Gary

 

The time to get worried is if the sparking travels a 360° around the com, usually a sign of a partly shorted armature.
Also there are two types of com bar insulation, when a com is re-cut or turned down or even wears down, if it is constructed with mica insulation, this has to be 'undercut' usually with a very small hacksaw blade with the teeth setting ground flat.
Many modern com's use a automatic wearing insulation that does not require undercutting.
Max.

 

As always, you share a lot of good to know stuff.
Thanks,
Gary