1979 Charging System

[bbelk]

I had three stops on the way to work this morning, and on the last one, my 1979 R65 wouldn't start.

Battery is 3 years old.

After bump starting it, I noticed the generator light on at higher RPM than normal. It didn't fully go out until 2,500 RPM.

So - when I get home, whats the testing sequence?

Thanks in advance.
Brad

[dwerbil]

Brad, I'd hook up a good voltmeter to the battery cables, then start the bike. Rev it on up and watch what the meter does. If the meter reads only around 12 volts when you rev it, it's probably your voltage regulator that needs replacing.
Is your battery a bit weak....how the starting this morning sound?
Others will weigh in with other ideas.

[Kurt in S.A.]

Snowbum has an article on this.

Rob Frankham used to have article for testing the charging circuit on his website; seems to be gone at this point.

Kurt in S.A.

[bbelk]

Three bump starts, 18 miles, and a short trailer ride and I made it home with 7 volts left in the battery. Its on a charger now and I will start diagnoses when its off life support.

[Jean]

If it is a wet battery, check the electrolyte. No use wasting time charging a faulty battery. if your charging system is OK, the battery might have a dead cell. or 2.
3 years might be a problem, depending on how it's been used or charge maintained.
I have 2 of those fancy sealed batteries. One is good after about 7 years. the other died (failed to charge up sufficiently) after only 2 years, and quite suddenly!! since it was sealed there's no way to "check it" but it's charged voltage is only around 11.8 volts; that suggests a faulty cell. It WILL start the lawn mower...Not the R100s.

[bbelk]

The battery was charged all night with a 2 amp automatic charger. Voltage was 13.2 on the charger and 12 a few minutes after I took the charger off. The bike started fine. At 3,000 RPM the voltage is 13.2.

but (and this is new)

The generator light is on at an idle and doesn't go off until about 1700 RPM

[SteveD]

The generator light is on at an idle and doesn't go off until about 1700 RPM

When that happened to me, the rotor failed eventually. EDIT: then I had NO LIGHT AT ALL

Replaced it, and the red GEN light behaved normally.

There was a failure in the winding where the red dot is...it's covered by resin there, and the resin had cracked, along with the wire. I wonder if it was an incomplete crack...but only for a while.

[bbelk]

The generator light is on at an idle and doesn't go off until about 1700 RPM

When that happened to me, the rotor failed eventually.

Can I detect a failing rotor with an ohm meter without having to pull it from the bike?

[dwerbil]

If it is a failed rotor, I bet Mikey would have several used ones on the shelf.

[Robert C]

I had a similar situation a few years ago. Finally the red light went to full bright and that was that. Wasn't the regulator. When I pulled the front cover the diode board was visibly failed. Replaced the diode board to no avail. Turned out the rotor was bad as well (tested okay at rest). I think the diode board must have partially failed first, followed by the rotor.

Bob