R-65 Today's Charging system frustration

[R65john]

Sorry if this problem sounds duplicative, but here it is....

1984 R-65 42,000 miles

Recently installed new battery....Odessey Brand...seems to be working fine.

Red generator light has ceased functioning during the present electrical problems.

13.7 volts at 3000 RPM into partially charged battery

Current has not been measured. My mechanic doesn't have the toys needed to measure amps.

Twice now the cycle has died due to lack of current while travelling at highway speed, so the 13.7 v. must not have
sufficent amps to carry the lights and ignition.....

Suggestions? Sympathy?

[montmil]

If the GEN bulb is burned out, there will be no charge passing to the battery. That little bulb is part of the exciter circuit that, well, wakes up the alternator and gets him to go to work. Check the bulb.

[dwire]

Regardless, once the root cause is isolated and cured, it surely is not a bad idea to add a small resistor in the circuit there at the lamp (or elsewhere in the wire - I chose the lamp area in the bucket so I would not "lose" it at one point or another if it needed attention...) as I' did some years ago once realizing how the system worked. There is a great writeup on .... Let's see ahh, I guess Snowbum's site. Look there, it will explain a few things and as well guarantee that even with a burned out bulb in the middle of nowhere, your charging system should not fail to operate. Unsure if my modifications were the same as his article is now dated 2011 and I did my first one of those mods to my ex's bike maybe 6 or so years ago.

http://bmwmotorcycletech.info/genlampresistor.htm

Also, if you are interested in any of the plethora of articles and data he has there, wipe out everything in the address to the, "http://bmwmotorcycletech.info/" and you should be able to find an index of sorts somewhere. His site is full of all manner of BMW and related articles right-ups and the like - I think the only thing it really truly lacks is a very good organizational method; but the first hyperlink above will take you directly to his newest description of the simple generator lamp (alternator) resistor modification page. The infamous Duane A. may as well have this data up or refer to it, I am not sure; I just for some recalled reason it being at Snnowbum's site perhaps it has been suggested here recently enough. You could Google it too... Good luck.

[R65john]

Wow ! Who would have ever thunk of one little indicator bulb?

The previous bulb only lasted 28 years, so I might just try to see what happens without using the resistor.

Wishful thinking, and I hope it works because the thought of having to pull the tank, front engine cover and whatever else is needed to get to the alternator sounded like a lot of $$$$$$$$

thanks for your prompt assistance and hopefully great news

[Jean]

Where are you measuring the voltage: 13.7 volts? At the battery? How much does the battery show when it's not being charged?
The others are correct, if the gen light does not light, you are not charging thru the alternator...unless it's been modified already. I take it the light does not come on when you turn on the key switch and before the engine starts...is this so?
If you have enough current to operate the starter, you certainly have enough to run the lights and ignition.
If you are running and the ignition SUDDENLY fails, you have another problem, especially if the starter will still operate.
Please fill-in the "blanks"...does the starter still operate when the bike fails?

[dwire]

Where are you measuring the voltage: 13.7 volts? At the battery? How much does the battery show when it's not being charged?
The others are correct, if the gen light does not light, you are not charging thru the alternator...unless it's been modified already. I take it the light does not come on when you turn on the key switch and before the engine starts...is this so?
If you have enough current to operate the starter, you certainly have enough to run the lights and ignition.
If you are running and the ignition SUDDENLY fails, you have another problem, especially if the starter will still operate.
Please fill-in the "blanks"...does the starter still operate when the bike fails?

Jean, you are spot on; I was ahead of myself... For me when I read something such as the OP's post, it is easy to take things such as the obvious, "Does the engine still crank over when the bike dies???" for granted as something the OP would have already noted and just left out (meaning the bike or more accurately, the battery is DEAD) as his voltage quote is about what one would like see from a fully charged battery, either fresh off the charger, after a good little run on the bike, or for some systems with the regulators set lower than I prefer (lol, - that is without boiling the electrolyte or overheating the battery...) what one might read with the bike running and a fully operational alternator doing its job, right off the battery posts.

Good thing you and others are around to point out the obvious omissions in his description of the issue... - and of course my glossing right over them!

So, "R65john" I apologize, the flowchart in this thread would be to skip my initial post and head right to Jean's queries. Then when all is tip-top, perhaps consider the resistor addition as a fail-safe to a possible future Gen-light bulb failure...

[R65john]

Thanks for the follow up inquiry. I am experiencing a charging system problem and not an ignition problem.
It appears I have been operating on battery charge alone, and when the battery loses all potential, the cycle stops.
The 13.7 v. was measured prior to the lamp failing. At that time I replaced the BMW (Excide) battery with the Odyssey brand. The light has subsequently failed.

The generator light does not come on when I turn on the switch.

I doubt that I have any output from the alternator now as the cycle has quit at highway speed, subsequent to obvious dimming of the headlight.

The only factor not previously mentioned was that all of the electrical issues have occurred in continuous 110 degree weather, never experienced before.

Appointment later this morning with the mechanic. I did purchase some 330 ohm resistors, but in retrospect the previous generator lamp lasted 28 years, and I assure you I will not last for another 28...Might just have the mechanic change out the lamp and see what happens.

Since my original posting, I purchased a digital voltmeter that plugs into an accessory cigarette lighter socket, so
I should have some quick grasp if the problem is resolved.

Fingers crossed/ I'll let you guys know.

thanks

[SteveD]

Have you tested the GEN bulb in another socket on the circuit board? It's just as likely to be ok, and if so, the likely cause is a duff rotor. They're cheap enough from EME and very easy to replace, but you will need the hardened bolt to extract it...any old bolt will not do.
Test the bulb, then test the rotor...before pulling stuff apart.

[Duane Ausherman]

R65 John, Your explanation tells us almost nothing of use, sorry.

You must measure voltage correctly or you will only confuse yourself and us. When not under charge, the battery voltage measurement means almost nothing.

Even a fully charged battery tells you nothing about the capacity. As a battery ages, the capacity is constantly reducing. So, a fully charge battery with 1/4 of the original capacity is useless, but does measure correctly.

You either need to know about electricity or follow a good article exactly.

Replace all of the bulbs in the headlight shell and then you can be fairly sure they are OK. Measure resistance across the rotor to know if it is open, or working.

[Deleted User 287]

Measure resistance across the rotor to know if it is open, or working.

But what if it's one of those damn rotor faults ("opens") that only occurs at speed?