I've had a VDO analogue voltmeter on my '82 with stock charging system for several years, powered off the brown wire coming out of the ignition switch at its connector in the headlight bucket, as far as I know giving reliable readout of voltage. My battery is fairly new AGM type, about a year old; my battery charger also is maybe a year old, with capability to recognize AGM batteries. My rotor is a Racetech installed July 2013, with about 3400 miles on it last Fall when I began to notice that, after riding 15-20 miles of mixed town and country with plenty of 50-55 mph stretches, the needle began to fluctuate rapidly and erratically around 14 VDC, swinging roughly from 12+ to nearly 15 at most. This occurs on both smooth and bumpy pavement, so I do not think it's related to road surface roughness. The oscillation decreases as the bike slows and disappears at idle (1200-1300 rpm); then resumes as rpm's rise and voltage increases to 14+.
During the first 15-20 miles, before the oscillation begins, the voltmeter needle stays steadily on 14.2 above 2000-2500 rpm, decreasing to low-to-mid 12's at idle (I've got LED headlight and taillight bulbs and LED turn signals and running lights front and rear). Therefore, I don't think there's anything wrong with the meter damping.
I've cleaned the rotor rings, installed new brushes, cleaned the red and brown terminals on the ignition switch pigtail and the brown terminal at the rotor and have gone thru much of the charging guide. Contacts inside the ignition switch itself were cleaned 5 or 6 years ago; maybe 3000-4000 miles ago. (Four very young grandkids moved near us 4 years ago; I don't ride much anymore.) Slap test good; ring-to-ring rotor ohms consistent at 4.6 over 10+ paired readings at various points around their circumference (at low end of spec, I know); infinite resistance from both rings to ground at multiple paired points. Stator ohms leg-to-leg consistent at 0.5 for all three white pairs; infinite resistance to ground on all three legs. I haven't checked running AC voltage since the bike appears to be charging just as it should for the first 15-20 miles.
I've observed this voltmeter needle oscillation with two different rectifiers on the bike, a Fiat unit I put on last Fall and then also this Spring after removing that one and re-connecting the stock rectifier, so at this point, I don't think it's a bad rectifier - could be both are bad, I guess, but that seems unlikely.
I'm no electrical guru, but from what I've observed and described, it seems like the oscillating begins about when I'd expect the battery to be fully recharged after an ambient (i.e., not warm-to-hot engine) startup, and the rectifier needs to begin limiting generator output to avoid overcharging the battery. At this point, I'm stumped about what to check or do next - any and all ideas are welcome. Bad ground somewhere? Too much load taken off the generator with all those LED replacements?
During the first 15-20 miles, before the oscillation begins, the voltmeter needle stays steadily on 14.2 above 2000-2500 rpm, decreasing to low-to-mid 12's at idle (I've got LED headlight and taillight bulbs and LED turn signals and running lights front and rear). Therefore, I don't think there's anything wrong with the meter damping.
I've cleaned the rotor rings, installed new brushes, cleaned the red and brown terminals on the ignition switch pigtail and the brown terminal at the rotor and have gone thru much of the charging guide. Contacts inside the ignition switch itself were cleaned 5 or 6 years ago; maybe 3000-4000 miles ago. (Four very young grandkids moved near us 4 years ago; I don't ride much anymore.) Slap test good; ring-to-ring rotor ohms consistent at 4.6 over 10+ paired readings at various points around their circumference (at low end of spec, I know); infinite resistance from both rings to ground at multiple paired points. Stator ohms leg-to-leg consistent at 0.5 for all three white pairs; infinite resistance to ground on all three legs. I haven't checked running AC voltage since the bike appears to be charging just as it should for the first 15-20 miles.
I've observed this voltmeter needle oscillation with two different rectifiers on the bike, a Fiat unit I put on last Fall and then also this Spring after removing that one and re-connecting the stock rectifier, so at this point, I don't think it's a bad rectifier - could be both are bad, I guess, but that seems unlikely.
I'm no electrical guru, but from what I've observed and described, it seems like the oscillating begins about when I'd expect the battery to be fully recharged after an ambient (i.e., not warm-to-hot engine) startup, and the rectifier needs to begin limiting generator output to avoid overcharging the battery. At this point, I'm stumped about what to check or do next - any and all ideas are welcome. Bad ground somewhere? Too much load taken off the generator with all those LED replacements?
Analog meters still have their place -- you can tell things from a swinging needle that you can't from a changing jumble of numbers.
