Boxerworks.com

I need help troubleshooting what is causing my dash panel battery light to intermittently go on and off. It goes from bright red at higher rpms, fades at lower rpms and sometimes fades at higher rpms. Some background on the bike and recent charging issues:

Bike - 1992 R100R
Mileage - 29k
Battery type, age - wesco sealed, age unknow as I've owned the bike since october 2012

Recent performance - kept battery on BMW trickle charger last winter, rode occasionally last winter, rode 5k miles over last 12 months without issue.

Recent issue - battery was dead after sitting for 2 weeks, recharged then rode last week when light started coming on. Went for 2 hour highway/backroad ride last Saturday and light never came on. Went for hour long ride yesterday and light started coming on after 45 min of riding 3500-4500 rpms.

Troubleshooting so far - connections checked visually, need to remove pos/neg cables and reinstall. Also will check alternator output voltage under load. Need to check alternator but don't believe this is not the issue as I'm thinking recent charging cycle did something to damage battery.

Any other ideas are much appreciated, thanks for the help!
Charlie

I moved his OT, and deleted yours, so that link will probably dead-end...
I also deleted the ghost. I never did like those things.

edit: welcome aboard! I haven't read your issue yet. That is next.

Well, I am sure it is something specific, and I will let smarter folk fill in there.

I will say with certainty that you should inspect and clean all of the major connectors on the bike, making sure they are as bright & shiny as possible, and reassemble with some sort of grease to act as a dielectric.

Have you had the front cover off of your bike yet? Do you know to disconnect the ground at the battery (check for any accessory grounds at the battery) before you remove the front cover, to prevent shorting of the diode board?

Are you familiar with a VOM?

I had a similar thing with my 94 R100 Mystic.
Turned out to be the alternator rotor. The varying RPM would make the broken contact touch, which would dim the light. Also, with the key on, motor not running, the light didn't come on at all.

Seapbmw, if you don't already know about Rick at Motorrad Elektrik http://www.motoelekt.com/ you might want to bookmark that link.

Like Seth said, a alternator rotor can have a break that only opens up at speed. Bench testing (or with the engine shut off and the brushes pulled back) can often show continuity, that goes away at speed when the break opens up.

If that did indeed turn out to be the case, I would shop with Rick, unless you can buy a good used one from a trusted source.

But if you like a lot of electrics on your bike, like heated clothing/grips and/or high wattage lights (conspicuity), you might want to invest in one of the higher-output options that are available.

I'll toss my vote for rotor intermittent connection, too. It's spinning fast and that's why the connection can change...

Don't go using the shot gun approach, as that will waste time and money. Start with logic and do the testing.

It costs nothing to measure the charge voltage, this tests the alternator. It costs nothing to do a load test of the battery to get a rough idea.

The only way to test a rotor for sure is to swap it out.

There are plenty of websites with this info.

I'm sure a 'Megger' ( Insulation tester ) would expose a dodgy rotor.The high voltage should do the trick.
Find a mate who has one or get local auto lecky to do it, and test across the slip rings. A good rotor will show as a short.
Can also test each slip ring to the shaft ( should be infinite resistance ) Make sure you test BOTH slip rings....