Monday, January 13, 2014

Debugging the Charging System w/More Pictures

Updated photo of the
alternator with labels
I finally dug into the charging system problem that I mentioned a couple of posts ago. To summarize, when leaving the Silver Gulch Monday evening, I noticed that the GEN light did not light up when getting ready to start the engine. This means that the charging system was not working and the problems could range from a burned out indicator light to a failed rotor and everything between those two points.

Exhaust Nuts
To reach the alternator, I needed to remove the fairing front lower, the mufflers, the exhaust headers, the rear engine mounting bolt, the oil cooler and finally the front alternator cover. It turns out that I didn't need to remove the exhaust system as the alternator cover is separate from the front cover. But I needed to renew the high temp anti-seize on the exhaust nuts anyway.

Alternator brushes and
slip rings
I removed the plug from the "DF" connector on the alternator which provides power to the rotor through the brushes and connected the plug to ground. After reconnecting the battery, I turned on the ignition and lo and behold the GEN light is on nice and bright. Darn, this means that the problem is more major.

Schematic of the BMW
airhead charging system
I then used an ohm meter from the DF terminal to ground and it was open (bad). DF terminal to the forward most slip ring on the rotor and 8 ohms (the brush was good). DF terminal to the second slip ring, open circuit (very bad). This means that the rotor has a broken wire somewhere within the windings. Major problem.

Original Enduralast aftermarket
charging system
I have multiple options at this point. Look for a replacement rotor preferably new. Or upgrade the alternator to one of the two aftermarket options. Since I have been looking at the aftermarket options for a couple of years, I decided to go with the original Enduralast system which replaces the alternator, the diode board and the voltage regulator. The other aftermarket option produces slightly more amps but at a much higher RPM and still uses all the other parts.

Diode Board
The stock system generates 24 watts at 1050 rpm and 280 watts at ~4000 rpm. So until you hit at least 3000 rpm, the battery is not being charged. The Enduralast system produces 100 watts at 1000 rpm and it max of ~450 watts at 2000 rpm. So even running around town, the battery will still be charging. And I don't really need to be worried about heated gear or auxiliary lighting. As you can see, there are very few parts to the new system.

On the Enduralast system, the rotor uses a permanent magnet so there are no slip rings or brushes and the stock problematic diode board and discrete voltage regulator is replaced with the integrated rectifier and voltage regulator. I have been wanting to upgrade to this system for a couple of years but it was hard to justify since the old system still works. I am still wondering if the addition of the larger battery and charging load contributed to the failure of the old system.


Unknown said...


Sounds like the perfect solution. Simpler is better as long as it works. So sorry for the expensive solution, but perhaps it will be worth it in the end as it solves all your power requirements

Plus now you can install a heated gear socket for the Monkey

More Watts may also mean more power from your engine at lower speeds, due to better sparking and fuel combustion, perhaps new high performance coils ?

Riding the Wet Coast

Lucky said...

Well, it's always a drag when something breaks, but when you can replace the broken bit with an upgrade you wanted anyway, it all works out.

Glad to see you didn't get stranded either. I imagine push-starting your bike is a little tougher than it is with mine.

Dar said...

It seems anything 'fix' related on a bike is an expensive proposition. At least though you won't have to be worrying about being dead in the water so to speak and now you will be toasty warm because you can plug in gear.

RichardM said...

I've been looking at comparisons between the two aftermarket systems for a couple of years. The stock system was adequate as long as you rode long enough at higher engine speeds to charge the battery.

No new coils as they're not needed.

RichardM said...

I was thinking that I could just continue riding without an alternator and just charge the battery every evening but opted to replace it.

Didn't expect a failure without warning like that. Now I know why some opt to carry a spare rotor on long trips.

I don't think it would push start very well. Now, if it had a kick starter...

RichardM said...

I was plugging in gear but I would always make a point to turn it off when leaving the highway so it wouldn't run the battery down. Since I put a car battery in the sidecar, I haven't worried too much about it. I have noticed that as the week progresses, the battery voltage slowly drops suggesting that the bike charging wasn't quite able to keep up.

At least it is a simple swap (I hear).

redlegsrides said...

The Enduralast is a bit pricey but I think you'll be happy with it RichardM. I plan to go that route when my own airhead's charging system bites the dust. Great writeup on the steps you took, any chance of pictures of each test point? I am not familiar with the setup so was unable to reference it to a visual. Or is there a link to where the diagnostics you followed are accompanied with pics?


RichardM said...

I'll add more pictures tonight. I just dug into it after looking at a wiring diagram for the charging system. It's pretty straight forward. BMW wants $459 for a new rotor, after market rotor $79. But because I ride in the winter, one of the optional charging systems seem to make sense. Omega, the original Enduralast or Enduralast II. I opted for the original Enduralast as the others still have the VR and diode board, albeit updated versions. Also the original Enduralast will even charge at idle. The Omega and Enduralast II use better Bosch parts and produce 450 and 400 watts respectively but not until 5k rpm. I'm rarely above 4k rpm.

VStar Lady said...

Glad you found a solution ... very few parts, the trick is getting them in the right place. Hats off to you!

RichardM said...

I hear that installation in only a couple of hours. The wait for USPS is probably going to feel like forever. (The website claims delivery by Thursday!)

Troubleshooting these kind of problems is pretty straightforward.

Conchscooter said...

All those lonely dark hours in a shed in Barrow with a bear guard finally paid off. I could barely follow the science but I'm glad you're happy with your new wiring.

RichardM said...

I don't have my new alternator yet but looking forward to getting the rig back on the road!

The shed was too long of a walk through the snow. Didn't go...

redlegsrides said...

Thanks for the additional pictures Richard, the procedure is clearer for me now. Not crystal but clearer. I'm the type who has to actually do it to learn it. :)

Unknown said...


You may have a point about your marginal charging system having to charge a larger capacity battery and being unable to do this for long periods, which basically, fried it

There is this same problem with C4 corvettes where if the battery is not near full charge, will fry the alternator. It happened to me twice, plus I had to buy new batteries every 2 years.

Your new system sounds like a great upgrade

Riding the Wet Coast

RichardM said...

No real procedure that I followed but just tested things in sequence cutting the system in half then worked my way in. Actual time including disassembly was maybe 30 minutes. I needed to pull the mufflers to get to the transmission spline anyway and now need to remove the air cleaner housing, top cover and starter to pull the diode board and mounting posts. I needed to clean the starter anyway and probably replace the nose bushing. I think the starter has been dragging. Much of this also needed to be removed anyway.

RichardM said...

With the stock Bosch system, as well as with a couple of the aftermarket ones, current is fed to the rotor through the slip rings to magnetize it. The higher the current output the more current sent through the rotor. A byproduct of this current is more heat generated in the rotor. It's easy to see how this heat could cause failure in the rotor windings. The permanent magnet rotor on the Enduralast system eliminates this heat and one of the comments I heard about the Omega aftermarket system was how hot the rotor gets.

But this is probably more detail than you want on a charging system.

VStar Lady said...

Only if you know what you are doing Richard!

RichardM said...

There's an assumption there… We'll see if it starts up again.

David Masse said...

Richard, I hope you have a nice well-lit and warm place for the wrenching. You make it sound simple, but it's very impressive. Sounds like your rig is headed to electrical paradise.

RichardM said...

I do have a "heated garage" though the temperature inside depends on the temperature outside. But it has been shirtsleeve weather inside for the last couple of days. Hopefully it last through this next weekend.

I am doing a bit more disassembly than I need as I want to do one other bi-annual maintenance task while I'm at it. Greasing the input splines on the transmission and checking on the condition of the starter.

VStar Lady said...

I have faith ...