Thread: arcing angle grinder

Check that the brushes can slide freely in the holders.
Check that the brushes are bedded correctly to the commutator (fine emery paper wrapped around the commutator is a way to re-bed the brushes.
Check the commutator itself (clean up with fine emery paper) - and the insulators between the segments (they should be slightly recessed to the segments).

Does the motor have any capacitors across the brush holders? These might be gone?

There is a capacitor in the parts breakdown, but it might just be between active and neutral

http://www.metabo.com.au/fileadmin/m.../602528XX2.pdf

brushes slide easily... Have not pulled it apart to check anything else yet...

Originally Posted by .RC.

There is a capacitor in the parts breakdown, but it might just be between active and neutral

It is hard to tell from a exploded diagram.

I'd be inclined to check/clean the commutator and see if it makes a difference.

made no difference.. I will take it to the doctor...

you might have a segment starting to lift off the comutator or the fielf has has an open circiut

Hi all,

the capacitor is connected across the motor leads (parallel mode) and is housed in the hind grip. If it shows no signs of inner shorting effects (bulbous shape, cracks, parts of the contents leaking or sticking out, or black smoke or burn residues), it's usually still okay.
Commutator and brush arcing can be caused by dirt or grease, imperfect commutator drum roundness or motor coil faults. The motor may have sucked in fine but gritty debris during grinding activities, causing temporary scratching or soiling of the commutator copper. This will be gradually remedied during further use, with the arcing returing to normal level. But there may also be motor coil damage. Anyway, it is never a good idea to keep on using a noticeably arcing power tool without proper inspection. It's better to be sure and to prevent further damage.

Take out one brush and remember how it was mounted, because you must replace it in exactly the same way. If replaced in a 180 degrees turned way, the contact surface between brush and commutator drum will not be the same and the arcing will be much more violent, causing even higher risk for the capacitor, the motor windings and the commutator surface smoothness.
The concave contact "wear" surface of the brush must be smooth and shiny, without fretted or burned edges. Scratches in running direction point toward debris (the gritty sucked-in dirt as mentioned above) between carbon and copper, during machine running. If so, slight scratching lines may also be visible in the copper. Treat the commutator drum with very very fine waterproof sanding paper as mentioned in a post above. For real damage you will need a precision lathe for proper treatment. For commutator treatment you need to at least remove the hind grip, to gain better access to the commutator. For myself, i favour to take out the entire armature to be sure that the commutator polishing ends up as a thorough job. For mere cleaning, toilet paper wetted with a bit of white spirit will do the trick (the paper should not drip but only be moistened; no loose fluid should touch the windings and use dry new toilepaper to absorb any spirit remains afterwards). Also clean the brush carbon from all sides. If the machine is noticeably soiled from the inside (which happens sursprisingly quickly with intensively used angle grinders), the soiling may also have lodged inside the brush holders, imparing free sliding movement of the brush carbon inside the brass holders. That is often another reason for sparking (going together with unsteady motor running).

If the brush edge is decayed at the contact surface's leading edge, dirt has damaged the brush and maybe the copper. In that case inspect and remedy. If the trailing edge is damaged, this is often caused by arcing. This can be caused by either dirt or grease on the commutator drum (poor or irregular commutation contact) or by abnormal currents. In the latter case, the motor current is too high and the reason for this must be found. A thorough inspection of all the commutator strips must be carried out. If one or severl of these strips also have frayed edges, a brighter copper colour or a darker shade, those particular strips have been exposed to high current and heating, in which case there is internal coil winding shorting. I advise you to have the machine checked with special equipment (like induction current detectors) to determine if there is real motor damage, if there are visible irregularities on the commutator drum. The armature is the most costly motor component, but if you should carry on working with a damaged armature, the field and capacitor will go as well. The total repair costs will then exceed half the machine's purchase price, which in insurance terms is called a "total loss". So be sure as early as possible.

Good luck!

gerhard