charging system woes- rotor resistance low.

[Sparky]

Hi guys. I'm having trouble charging.

The charging system is all stock 1981. It was working, at least to some degree, until recently when I had the engine rebuilt. None of the wiring was messed with, aside from unplugging connectors.

Ive read through gggGary's "expanded charging system guide", and I think I understand most of it. My job is working with DC circuits and voltmeters, so i'm knowledgeable there. My battery is good, and most of the testing ive done today was while hooked to a trickle charger. The diodes in the rectifier check out okay.

The resistance on the rotor is only 1 Ohm, the charging guide says it should be 5. Before I buy another rotor, is there any further testing I can do?

I'm not getting 12V to the alternator brush (the bottom left, the outside ring). in fact, that one read about 3 volts. the Inner ring brush reads 10.5. When I disconnect the outside ring brush, with key on, I get 0 volts to the outside wire and 12 to the inside wire. I also get less than 1 ohm resistance from keyswitch to inside ring wire. I attempted to run a hot wire from battery to the outside wire, to see if it would start charging, and it immediately popped the 5A inline fuse on my jumper wire.


So i've got 10.5 V on the wrong brush, and low resistance in the rotor. whats going on here?

 

[retiredgentleman]

Using a battery + jumper to the outside brush is the wrong thing to do. That is only to be done for the 1970 to 1979 bikes. For the 1981
the correct test would be to jumper a ground to the outside brush. The 5 amp fuse blew because you caused a short circuit.
Your voltage readings are about normal.
Yes the rotor is bad. You could buy a new rotor or have your rotor rewound. If you buy a new rotor from places such as Mikesxs, they are chinese (taiwan?) made products and the quality is always in doubt. Since you live next door to Alabama, you could get your rotor rewound by Customrewind.com. They have an excellent reputation for doing first class work.

Edit:
I just tried their web site and its not working. Perhaps their business is no longer in operation???

 

[angus67]

A member here had a rotor rewound by them last summer. When he started it, and the engine came up to temp, the laquer, or epoxy or whatever it is they use to seal it, flung iff all over the stator. They sent a good rotor claiming the rotor wasnt oven cured to set the epoxy. No more problems for that member, and maybe a fluke, but.......word gets around. They are the only place that gets talked about here. I would still try to get them to do one.