Over this past winter I spent a fair amount of time doing some upgrades to my '77 R100/7. Mostly doing handling, braking and cosmetic modifications. However, once the bike was back together and I started it for the first time, I've noticed an issue that wasn't there before. My generator light isn't behaving as it should. In fact, it seems to be doing nearly the opposite of what it should. At idle, the light goes off and once I'm on the throttle it comes on very brightly. Also, when I turn on the ignition, the generator light is also bright, as it should be.
My first thought was to pick up Rick Jones Classic Boxer Charging to see if it would lend some insight. In reading through his book, it seemed like my Voltage Regulator may have been the issue. But, I swapped out, what I believe to be a functional, used voltage regulator, and it did the same thing.
In full disclosure, I had one of the moments when putting the bike back together, that makes me feel a little less than bright. Fairly recently, I replaced the battery with a MotoBat. They seem highly regarded and I've been really pleased with it. However, these batteries have 4 connection points rather than 2. And I found out the hard way then the connections aren't symetrical. Obviously, I wasn't paying close enough attention when reinstalling the battery and had it sitting in the cradle backwards. I attached the positive terminal first and then when attempting to hook up the negative terminal, I was treated to an impressive sparks show. It took me a minute to figure out what I had done. I then swapped the terminals, turned on the ignition switch and everything seemed to work as it should.Â
This past weekend is when I finally had the bike ready for its first spin. It started just fine and seems to run with no apparent issues, other than the generator light burning brightly as I motor down the road. I'm wondering if I have fried the diode board or maybe something else. Any sagely advice would be greatly appreciated.Â
Much appreciated.Â
Bombadil
> You're correct. The signal for the dash indicator lamp comes from the voltage regulator.
> When hooking up a battery with reversed polarity, the diodes in the rectifier would be the first to be damaged. There are 6 diodes in the Airhead rectifier, 2 for each of the 3 phases coming off the alternator. If any one of those 6 blew out, then you'd lose 1/3 of your charging current, which would make the dash indicator light come ON.Â
> In the old days rectifiers were sometimes made of selenium, which was more bulky and more expensive, but blow out proof. The Airhead rectifier uses solid-state diodes which are far more efficient, but also more susceptible to damage.Â
> For the repair.... Buy a good used rectifier board. Buy the solid metal rectifier standoffs offered by Motorrad Elektrik. And then install the new board AND standoffs after applying a coating of No-Ox-Id anti-oxidation compound to: 1) both ends of the standoffs (these standoffs provide the Negative "ground" termination for the rectifier board) AND 2) every male electrical terminal before plugging up the connecting wires. This work will require removing the Starter Cover and the Front Engine Cover.Â
Link to Standoffs: http://motoelekt.com/charging.htm
Link to No-Ox-Id: Here
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you Wobbly. You always seem to be there offering your wisdom to us Airheads, as needed. We're lucky for that.Â
I am still going to remove the old diode board and test according to the Classic Boxer Charging instructions. However, I've also already ordered a replacement from EME. Sadly, I'm replacing the one I had recently replaced as part of a charging system upgrade. It's the one listed as Heavy Duty and I believe may be an Emerald Isle replacement part. When I originally replacing this part, the original rubber mounted standoffs were replaced with the solid metal variety. I will also take your advice and use some No-Ox-Id when reinstalling the posts and connectors. Hopefully this repair goes smoothly so I can get this bike on the road and enjoy some of the recent upgrades. Â
I will be sure to provide an update as to how the repair went.Â
Your advice was spot on. I changed the diode board and the generator light went back to functioning normally. I've attached a photo (hopefully) of the ruined board. If you look closely, you will see what I believe are the diodes on the Y circuit, that have fried and no longer have a gap between them. The other 3, W V & U, all still have a gap between.Â
Thanks for your help Wobbly in getting my bike back in shape. And be wary of the 4-connection, non-asymmetrical batteries when reinstalling. My inattentiveness cost me $100.Â
Bombadil
Advertisement
