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Posted by David Sherman on Tuesday, June 09, 2009 at 11:00:22 :
In Reply to: generator brushes versus an alternator change out posted by jeff s on Monday, June 08, 2009 at 23:27:02 :
Back when I lived in Everett, "Frenchy" of G & H Auto Electric would have done it well and enjoyed the chance to work on one of the old units. When I needed a 6 volt regulator for my dozer, he found an NOS one on the shelf, gave it to me for nothing because he said nobody would want one these days, and insisted on opening it up, putting it on his old tester machine and tweaking the voltage and amps limits to what he thought they should be. Unfortunately, Frenchy was old and he sold out to a couple of yuppies who would sell me a pair of brushes if I knew exactly what to ask for, but they had a surly attitude about it all and basically just wanted to swap out modern alternators and starters for people. Same thing happened with the old auto electric shop in Spokane. Couple of young guys took over and were more into installing sound systems and lights than rebuilding anything. If you can find one of the old guys whose still in business, treat him like the rare gem he is.
Another place to try for brushes is an industrial motor rewinding shop. There aren't too many of them left either, but there are a few. They generally have an old stock of brushes of all sizes and might have some that fit. In a pinch, you can take brushes that are a little too big (too long or too fat) and grind them carefully to the right size.
It's important to figure out if the brushes wore out prematurely. They should normally last a LONG time. Look for pitting on the commutator, or if the generator is still on the rig, run it while charging a heavy load and look for sparking. If a motor or generator is set up right and is in good condition, the commutator should not spark, or should spark only very slightly. Sometimes it's a matter of rotating the brush holder slightly to find a position of minimum sparking, but most of the time if there's much sparking, there's a shorted turn on the armature. The same goes for portable electric power tools. An old guy in a good auto electric shop can "growl" the armature to see if it's got a short, and if he's really good, he can re-wind it.
Be real careful about turning the commutator if it's rough. If it's very pitted, it's been sparking, and if it's been sparking, there's a reason. The reason is usually NOT that the commutator is rough and the brushes are worn out. Those things are the result of sparking, not the other way around. Sometimes they'll get worn down if gritty dirt can get in, and then you need to clean it up and turn it if it's bad, but I tend to treat old commutators like old brake drums -- don't remove irreplaceable material unless it's absolutely necessary. Minor scratches, in the direction of rotation, are best left alone. Whatever speck of grit caused it will be gone when you're done overhauling the generator anyway. If you do put it on a lathe, make sure it's centered perfectly,use a very sharp tool with a lot of rake, and take a light cut, because copper tends to stick and gall if you're not careful. For light polishing, if you don't have one of those special commutator polishing sticks, an ink eraser works pretty well. If you cut much copper off, you then need to cut down the mica between the segments, which is another reason not to start turning the commutator unless you really have to.
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