R100RS charging issue

The bike is a 1977 RS. I had a 400 watt enduralast charging system put in last winter. The other day when out for a good ride the volt meter would swing wildly when over 4k rpm's but would settle down when I lowered the rpm's. Today when riding in town the generator light goes off over about 2k rpm's but then glows faintly at over 3,500 rpm's and up. Bad regulator?

I would track down all the grounds in the charging system and make sure they're clean. Snowbum has some info on testing a regulator if you want to try that:

https://bmwmotorcycletech.info/testingvoltageregulators.htm

You might also want to touch base with the people who supplied the system and get their input. From your statement, you said "I had...a system put in". So some other shop put the system in the bike?

Sounds like your diode board is pooched. With the bike running, check for dc voltage at the battery. If there's more than .5 of a volt ac the diode board is the culprit. The bonus is, you don't have to take off the timing cover to test anything.

Woodgrain

volt meter and things

One thing to remember with BMW volt meters is they are not be all that accurate. I have two BMW airheads, one volt meter reads 5 volts lower than the other and responds differently than the other. They give a good idea/trend as to if your bike is in fact charging or not but I would not count too much on what they read, unless of course it is less than 11.5 volts.

The only way to test things is to get a good trouble shooting guide as suggested by Kurt. Then, use a proper test meter to do the testing. Only that way will you know what the true readings are.

There is a book out by Rick Jones of Motorrad Elektrik. Snowbum has very good tips as well as http://largiader.com/articles/charging/

Easiest thing to do first is check the grounds as has been recommended. Also make sure your battery terminals are clean and tight.

It would be easy for me to say because, the light is glowing above 2000 RPM the diode board is bad. It may in fact may be bad. But I do not jump to conclusions. I happen to have a spare diode board in my tool box but most people do not. No matter where you buy them, they are not cheap.

Better to spend a bit of time researching Snowbum or Arn, or spend 25 bucks to buy the book and make sure a part is bad before replacing it.

Regardless, let us know what you find out. St.

Relaxed Reading

If you want to learn about charging systems, Snowbum has a spot to learn all about it.https://bmwmotorcycletech.info/boxerelectrics.htm

I have used this site from time to time as needed along with others.
St.

The diode board was replaced about 200 miles ago with the rest of the electric system upgrade. But could still be the issue.

Who did the work?

So, who did the work? What system did you install? what parts, factory or aftermarket? Were any changes made to wiring when the system was installed? What other changes have been made to the bike?

If you did your own work, are you 100% certain all the grounds are good? Are you 100% certain the wireing is connected as it should be?

I agree, a new part can be bad after 200 miles however, it is pretty rare when you buy parts from established companies or factory parts they are going to sell something that would fail so soon.

Now if a part is installed incorrectly, for example; a diode board is shorted out during installation, it can fail.

A new part can also fail if there is something wrong with the wiring. I had a friend with a modified Harley. The previous owner had changed the headlight shell. In doing so, he had taken out the charging indicator light for the bike. Turns out, the charging indicator light is needed in the proper working of the charging system, (just as in a BMW system). NOT having the light in my friend's system ment the system was not charging and the bike was running only on the battery. I put the light back into the circuit and things worked well from that point. Changing the voltage regulator had no effect on the problem. ONLY by looking at the wiring diagram and taking the time to troubleshoot things led to the discovery of the problem.

As I have said, all the tips and tools are available for fixing the problem. Let us know what you find out. St.

First thing to check is that the onboard voltmeter is telling the truth. Use a handheld voltmeter and strap it to the bike and see if the handheld voltmeter gives you the same erratic readings.

/Guenther

The voltmeter on the bike is pretty much a non issue for me but the idea of the faint glow of the generator light at the higher rpm's is what concerns me. Being an electrical halfwit I'll see if I can figure out how to bond with my hand held voltmeter. All the new parts were from Euromotoelectric and installed by a highly reputable Airhead Guru.

When fully charged what kind of voltage should the battery hold? It is two years old, agm.

A fully charged battery will read about 12.5-12.7 across the terminals. But that is a static charge and doesn't really tell you much. Take the same reading when the engine is running at above 3K RPM...should be close to 14v. Or take the reading when cranking the starter...the voltage should not dip below 10v.

faint glow of the generator light at the higher rpm's

Click to expand...

Could be the brushes or their contact to the slip rings.

Could be the voltage regulator.

I exclude the diode board. If there would be a problem with the diode board you would always see a red (dimmed) light.

/Guenther

What say they?

Have you contacted Euromoto electric? How about the mechanic?

A voltage reading at 3500 RPM would be a very good thing to have. I recall from my old mechanic days, 13.8 to 14.8 was a good range to charge at. As Kurt stated the battery should be about 12.5 to 12.7 at rest.

Has anyone done any wiring changes on the bike other than installing the charging system? Is it possible you have a wire out of place or crossed?

I have no idea as to the condition of your bike, I am guessing it is in clean good shape and is well maintained.

If you are the second owner, you never know what the first owner did to the bike. I have seen some horrible things done to wiring.

Just to add to the story, why did you upgrade the system? The stock system is fine for normal use. The only real need to upgrade is if you are running a lot of lights, electric clothing and heated handgrips. I run my 78 RS with a stock system with no problems for charging. On my RT, I did upgrade to a higher output system because I have gotten older and love electric clothing, heated grips and aux. Lights. The stock system could not keep up with the demand.

More questions than answers from me. If you were nearby, I would be happy to help. St.

First off, my appreciation for all the responses. The bike had some failing wiring under the front cover that was causing some issues when I bought it. It has 39,000 miles on it. Build date of 11/76. I had been looking for a 77 RS for quite a while. I am an ok surface mechanic, set valves etc but I took it to a well known mechanic in the Mpls area because I knew it had some stuff that needed help and I didn't have the tools or knowledge base. I had him go over it from stem to stern as they say. It runs and handles pretty much as new at this point. As stated before, I've put a few hundred miles on it since and the faint generator light glow just started in the last few miles.

I have run the mentioned tests on the regulator and it checked ok.

I have talked to the guys at Euromotoelectric and they have been very helpful. I just got back from a moto trip on the GSA and am heading out to the BWCA so when I get back and have time get it sorted I will pull the front cover (ground wire removed first) do some lurking there with my meter and report on what the findings are. Thanks again.

I forgot to add, the bike was completely stock and unmolested, owned by an Airhead family.

Thank you

Thank you for the information. It makes it easier to think about what could be wrong.

Check the wiring that was failing and replaced. It could just be a loose wire or a misplaced wire in the system causing the problem.

At least, you are not chasing an intermittent problem. The light is glowing every ride and above 3500 RPM.

Beats the heck out of trying to find a problem that happens once every five or six rides or more. I have been there, done that.

Let us know what you have found. Good luck. St.

I wish everything was this easy. I finally had time to pull the front cover (retirement is so busy). The W connection on the diode board had come loose, totally unattached. Plugged it back in and went for an hour ride and all is good. Again thank you for the help.

Better go buy a lottery ticket!

Great news!

A simple inexpensive fix! That is great news.

If you don't buy a lottery ticket, buy one for the BMWMOA Foundation raffle. St.