Generator: Field wires, brush length, commutator etc

[bikemaniac]

Hi,

I decided to disassemble my 6V generator to have a look at it. It works and is able to charge but I wanted to inspect it,

1. Where do 6V generators typically fail?
2. My two field wires look REALLY old. They have the cloth wrapping and some of the leads close to the brush are broken. How can this be fixed? Can I cut the broken part out and replace it with a modern heavy gauge wire and solder it together or will the solder stiffen the wire causing a lot of trouble?
3. At what rate are brushes worn down? It seems that my brushes are not in a critical state, but are there guidelines on brush length reductions pr thousand miles or so?
4. Les Andrews says I can clean out the mica between the commutator bars by means of a hacksaw blade which has been reduced in thickness. Is there another, more simple way of doing it?

Lucas

[RonC]

If your going to rebuild it I would replace the field coils, have the armature checked and turned and the mica undercut. The brush plate and holders can be cleaned up and brushes replaced if worn. If you don't have the proper tools I would bring it to a generator starter rebuilding shop. They are around. I would paint the inside of the case with red gyptal paint to help insulate the new coils from the case.

[Joe K]

Generators typically fail in the armature. I have two generators bought at Amherst NH flea market bought as "cores" and both have the same issue of grounded armature. Fortunately not much invested at $3 for one and $5 for the other.

One of these I replaced the armature (bought for $25 from a respondant to my query about armatures here on this board) and the other is waiting a re-wind per the LeJay Manual. (one has to find the last coil wound and "undo" the armature in the reverse order of it's construction - there is only something like 60 feet of conductor on the WHOLE armature.)

Working on the field coils is best done with the coil removed from the generator. You'll need to explore methodology to remove the pole pieces here on this forum otherwise you'll probably be working in "close quarters" inside the generator housing. Best way to extend broken wires is with plastic insulated wire, a solder connector, and shrink tubing. You may be challenged in either case to get all the wiring BACK into the housing.

Technically a field coil can be "unbound" from it's cotton cloth wrapper, and a turn or two of the coil removed to extend the broken wire without a joint. One turn removed affects it little in total magnetic force. But unwrapping and re-wrapping the cloth can be challenging - and possibly upset the now 80 year old varnish insulation on the wires. Probably better left alone or replaced outright with new.

Carbon brushes can be used to the point where the copper connector wire shows at the commutator contact surface - but generally they are replaced when the mechanical support parts (guides, springs) no longer bring them to meaningful or reliable contact with the commutator.

Les Andrews is correct in using a hacksaw blade with the "tooth set" removed (done by rubbing the hacksaw blade on a piece of sandpaper laid on a flat surface.) Or use a commercial "undercutting" device powered by an electric motor in a lathe.

Both of these one has to be careful after undercutting to 'ease' the sharp corner of the commutator bar left thereby. A small file can do this or I use a sharp screwdriver held at 45 degrees and 'drawn' across the sharp edge - you'll see the line of metal removed. Two or three strokes at varying angles is enough to remove the sharp burr and make a good surface for the carbon brushes to pass from one segment to the next.

Actually, for undercutting I have done WITHOUT the hacksaw blade and just using the screwdriver. The object of this game is to undercut the MINIMUM necessary. Mica is abrasive to carbon brushes, and one doesn't wish to leave "pockets" where carbon or copper dust can lodge and short out the armature segments.

And when you're done servicing the commutator, you want to be sure to remove ANY carbon or copper dust from between segments using a dry toothbrush.

Heh. Sometimes a good undercutting and cleaning will restore a shorted out armature for reason of the accumulated dust.

And when smoothing the commutator, use only garnet paper perhaps 150 grit. DON"T use emery or aluminum oxide paper as both grits are conductive to electricity.

Good luck with this.

Joe K

[Tom Wesenberg]

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If you need to replace the front bearing, it's a 203 bearing. I would never turn the commutator unless it was badly burned or rough. Even then many times it can be made smooth with a mill file and spinning the armature in the lathe.

Buy an Atlas hobby saw from your local hobby store. The blade is thin and does a good job of undercutting. Start undercutting at an angle as pictured, then lower the saw into the slot to finish the undercut. .005" to .010" is all the deeper you need to go. After undercutting I spin the armature in my lathe and polish the commutator bars with 1" wide fine crocus cloth. I spin the armature both directions and apply pressure with my fingers to give the bars a slight radius on the edges.

A little missing insulation is no problem at the end of the field wire. If you think it might touch something, then you can give it a coat of liquid tape. It will dry to a soft black rubber coating.

If your brushes have at least 1/8" of movement before the brush holders hit the stops, you can go for several thousands of miles. With a smooth commutator, the brushes don't wear very quickly at all.