Thread: charging system
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Old 09-22-2009, 11:26 PM
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Originally Posted by bird 60 View Post
...When Dave gets on he'll be able to go one further...
Thanks, Chris.

Originally Posted by birdbrain View Post
I'm I ready to put this generator back on my car now? any thoughts ?
Rod, you probably did as well as the shop would. Just a few thoughts, if I may give a little background:
Generators are nearly bulletproof. There isn't much you can do to damage one. Cleaning the inside is a VERY good thing as carbon dust loves to conduct electricity to the grounded case, causing a short.

There are a few cautions. The copper commutator should not be sanded (at all) unless the shape is distorted (egg-shaped, tapered, oval, severly scratched, etc). Those brushes you removed conform perfectly to the commutator, and if they still have good length left, they should be put back in (**more on this in a moment).

Bearings need grease, but as you witnessed, too much grease will spread all over the inside of the case and all the carbon dust will stick to it. So, grease the bearings before re-assembly but don't go overboard.

Carbon (graphite) is a natural lubricant and it conducts with resistance. It also withstands lots of heat because we pump ~40-amps through it. Your brushes need to freely slide in their holders so proper spring tension can push each brush against the commutator. A buildup of heated dirty grease will cause the brush to hang. That's when trouble starts. Current wants to pass, but an air gap between the brush and copper segments will cause burning.

Two things need to happen before you button it up: Grab the brush by that braided wire, and pull straight up. Feel it slide in the holder without obstruction, all the way down. If your spring is pushing the brush way down the hole, replace the brush. When finished, leave the braided wire such that it can freely extend to take up brush wear, but it won't touch any metal parts around it.

**I have changed many brushes on huge DC motors. We never change them all at once. They need to wear-in to conform to the commutator with decent surface area. Your generator only has two brushes. If you get new FLAT-ended brushes, find a cylinder about the same diameter as your commutator, put fine sandpaper on the surface, and arc the new brush's contact surface to conform to the commutator. Being carbon, they sand easy. A flat-ended brush will only conduct at a line of contact passing too much current over a small surface until it wears-in.

INSULATORS: One of your brush holders is insulated on the back plate, and the other is GROUNDED to the back plate. So, power is produced in the armature; Positive goes out the insulated brush to the stud, and Negative goes through the grounded brush to the case. You can see how important that back plate is to your system's ground. The two studs you mentioned should be well-insulated and tight. Plastic can be brittle as long as it is not broken (and shorting the stud to ground). Fiber washers and sleeves work well if you need more insulation.

You can check each component with a meter during the whole rebuild process. While the generator is still on your bench, check for shorted field or shorted armature windings using the technique I described below. You can do this as well as anyone else, for a whole lot less money.

Hope this helps. - Dave
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