Electrical Demon

[awaffa2003]

Hey all,I just started riding my recently finished R65/R90 conversion, putting an R90/6 motor in my R65 frameand have just ran into some electrical issues. At first i thought it was just a dying battery but now i know it must be more than that. It was fully charged one day and after riding around town one day it was dead so of course i thought "ok ive been starting it on and off for a while so i guess that wore down my battery" put it on the charger and it got charged again but the next time i rode it, during my ride all the lights started going dim and my GEN light stayed on so again i went home and charged it. next day i took it for maybe a 40 mile ride and my GEN light stayed on most of the time except for maybe the last 10 miles so im thinkin "ok maybe it totally charged now and ill be fine" so i left the bike off the cahrger when i got home. this was last night and today i rode it maybe 20 miles to my friend's house, left it for maybe an hour, went to leave and the bike wouldnt turn over. had to pop the clutch and ride home with no lights..... where do i start???

[Crossrodes]

It sounds like your generator is not putting out.  

Do you know how to check if it is charging?

The second possibility is that you have a short somewhere in the system.  I would check out the generator first.

[montmil]

Stator brushes?

[Bob_Roller]

What is the voltage at the battery, when the engine is at around 4000 rpm ?

You need to do this check with a fully charged battery .

Seeing as how you've done a lot of work on the bike, you need to back over the electrical connections, to see if something is loose .

[Justin B.]

The fact that the charge light magically "went out" disturbs me.  I had an MG that did that, I thought, "Fantastic, it fixed itself", when in fact the bulb had burned out and I had to have the wife stop and hook up jumper cables every 5-6 miles for a charge until I got home!

[larstorders]

The occaisional return to charging, as the gen light goes out, suggests to me a break in the alternator windings, either the stator or much more likely the rotor. I've experiencd this a couple of times and still have reels of lacquered copper wire at the back of the garage left over from DIY rewinding attempts. Which did work, sort of. I'd check continuity across the windings as a priority, after chhecking the brushes are clean., it only takes two minnutes. Good luck.

[awaffa2003]

ok ill do some checks and get back to you guys. but i doubt it's the rotor cuz i swapped it with the one on the '65 its the shiny one. ony thing i couldnt swap was the field coils again the shinier of the two.

[Ed Miller]

I thought that R90s used a different alternator than our bikes, a 240 watt one or something like that.  Ours should be 280 watt.  So I wonder if there might be some mis-matched parts.  Here are a couple of articles on the charging systems:

http://[http://bmwmotorcycletech.info/altcapability.htm/url][url]http://bmwmotorcycletech.info/trbleshootALT.htm