92 R100R charging problem

[jblamey]

Just bought this bike. Dealer said all checked out but it is not charging the battery (and we wonder why dealers get bad rep, of course it was a Honda dealer and this was just traded in). I did check out the snobum website but was looking for specific voltage checks I can make at points in the wiring harness. This is what I know so far: The rotor reads 3 ohms, at the brushes 5 ohms, across the brushes, at idle I get 5.9 volts. Across the stator windings I don't recall voltages but I must recheck. At the battery I see 11.9 volts (and suspect diminishing) when engine running (no matter the engine speed), 12.5 volts engine off. My battery has been drained at least once, I hope it did not totally tank, I am usung a new smaller capacity battery in the interim. So I am thinking the rotor is good, the stator good, that leaves what poor connections between alt and battery, bad regulator, bad diode board?

J

[20774]

Rick at Motorrad Electrik has a pretty good book for doing these kinds of systems checks. Might want to consider getting one at some time. I don't recall what the ohms are supposed to be for the rotor...the later airheads have a slightly different number. You might want to a search on this forum...seems like these numbers were posted before. You did this with the brushes lifted off the slip rings, right?

Any chance the brushes are worn out and not making good contact with the slip rings? Sometimes they get wedged in their holders and/or the snail spring doesn't have enough push on the ends of the brushes to force them down on the slip rings.

Snowbum gives instructions on performing voltage regulator checks by bypassing the regulator as well as doing checks of a regulaor on the bench. I recently did the on-bike bypass test. Voltage at the battery went up to around 16v at a decent RPM so it seemed to show that the basic charging system was OK. For grins, I ended up replacing the mechanical regulator ('78 /7 bike) with a new solid state type.

There have been some recent articles in the MOA News by Matt Parkhouse on how to perform bench checks of the diode board. You might want to give the board a quick visual to make sure there are no burned components. Definitely pull all connections for cleaning and ensure they are tight when slid back on.

Kurt in S.A.

[rinty]

JB

With your professional skills, you're the perfect guy to own an airhead. I second Kurt's suggestion to get Rick's airhead electrical systems book, and it's an interesting read to boot. Airheads have some electrical features that can fool some general mechanics, and this is perhaps what happened in the Honda shop. If you want more information, I would suggest that you have a look at the airheads site and there will be lots of threads on charging issues there.

One final suggestion is to install an absorbed glass mat Odyssey battery. I had an airhead for 15 years, and I think this is one of the best helps you can give them.

Welcome to the forum.

Rinty

[20774]

Here is a good article on the BMW charging system. It takes a little more than my EE101 edumacation, but still it helps to understand where all those little sparky things are going...

http://www.buchanan1.net/charge.shtml

Kurt in S.A.

[rinty]

JB:

And if you want more electrical output, you can install a 400 watt Omega system. My tech has one in one of his GS's and really likes it. I had the stock 280 watt system in my bike, and it worked fine, but I never ran any heated clothing or auxiliary lights.

Rinty

[35303]

The approach I took is to ditch the Bosch system and replace it with the Endurolast alternator. It works very well.
http://www.euromotoelectrics.com/EDLBMW.html

[The_Veg]

I'll second the vote for Motorrad Elektrik- either the book or the Omega system, in fact I'll vouch for anything from Rick (BTW I *HIGHLY* recommend the LED taillight he sells).

[jblamey]

Thank you to all who replied. Some very good advice I think.

I took a good look at the diode board and discovered that three of the big diodes had fried and the ground wire from the board to the engine case was a bit toasty but intact (melted insulation).

So besides the diode board I am thinking the regulator as well, wouldn't hurt to have a spare, they're small ;-) The dealers in my area closed on Mondays, huh? Coming from automotive retail, we were 7 days a week, dealers 5.5 days a week.

The rubber mounts for the diode board look to be 100% so remounting it solid should not be necessary.

Based on what I read off the web, the Buchanan article in particular, they say stators hardly ever fail, then moreso rotors, regulators and diode boards most likely, or opens/shorts in wiring. As far as I can tell via the meter there are no shorts and no opens.

BTW: I found the breather from the gas tank hanging loose because the end cracked, easy to put back on, and what looks like a hose from the bottom of the tank to the top of the crankcase was broken in two. So this problem with charging has had a side benefit of finding these two other issues. It may also be indications that SOMEBODY had the tank off trying to troubleshoot this issue and maybe decided to trade it in instead of fixing a charging issue. Hmmmm... Gotta go work on my bicycle now!

I'll keep you posted as to what else I find. Thanks again.

Jeff

[rinty]

Jb:

I seem to recall that there is a later and greater diode board available. You can check with Rick. Also, there is a "spider" (triple) groundstrap upgrade available from BMW, but it may already be installed in your later model airhead. It installs in the vicinity of the diode board. For the regulator, get a 14 volt "police special" one.

May as well do all the good stuff now while you've got it opened up.

A popular mod is to cut the bottom part of the ring on the end of the battery groundstrap where it bolts onto the engine case. Then all you have to do to disengage the ground is back off the 10 mm bolt a bit and it'll pull right up. Make sure you disconnect the ground before pulling off the front engine cover!! Some keeners like to hook the bike's voltmeter right up to the battery, as it reads a bit conservative the way BMW wires them.

Rinty

[20774]

Rick can hook you up with most of this stuff, although there are other automotive options for the regulator. Borg Warner makes a replacement as well as Transpo. I believe Rick sells the Transpo, both fixed voltage and adjustable.

I'm surprised there are rubber mounts on the diode board. I thought BMW went to the solid mounts in the early '80s. Solid mounts provide better ground and heat transfer but can be a bioytch to install. DAMHIK.

The diodes can be replaced...check Snowbum's site out for info. You could pick up a new one (Rick, Thunderchild) and repair your original one as a spare.

Kurt in S.A.

[The_Veg]

My '95 had rubber mounts. Replaced with solid mounts when I installed the Omega board.
It would be a good idea to figure out WHY your board overheated before you throw too much parts-money at the bike. While on that subject, you should definitely use a cross-fit regulator as they only cost about 1/3 what you'll pay at a BMW dealer. Basically you want a Bosch-compatible external solid-state (MUST be solid state for 81-on bikes with electronic ignition) unit with a capacity of at least 33 amps. Such units are getting hard to find on shelves at auto parts stores these days though (since most cars in the last 30 years use internal regulators), and may need to be ordered. Most stores can get them in by the next morning and they cost about $30.

[pmdave]

One big (and expensive) error is removing the front cover without first disconnecting the battery ground. The cover can easily contact the diode board, shorting out one or more diodes. BTW, it's unlikely a Honda dealer would know this.

After years of trying every trick in the book to get the maximum watts out of the stock system, I finally sprang for the Omega alternator kit. Wish I had done it years ago instead of fiddling with the marginal stock system time after time.

The stock BMW diode board mounts on rubber cushions--theoretically to reduce vibration. But the rubber isolators require ground wires to the case, and the original (brown) wires were a little skimpy. The older R75 has the diode board bolted straight to the front case (with appropriate insulators). I wouldn't have any qualms about tossing the rubber thingies.

In addition to the other character faults, the exciter current for the alternator is delivered via the charge light in the instrument cluster, and that involves several wire and pin connectors, a light bulb socket, and a flexible circuit "board", plus several other contacts in the switches, relays, and fuses. It wouldn't hurt to clean up all these connections and replace the charge bulb.

pmdave

[20774]

In addition to the other character faults, the exciter current for the alternator is delivered via the charge light in the instrument cluster, and that involves several wire and pin connectors, a light bulb socket, and a flexible circuit "board", plus several other contacts in the switches, relays, and fuses. It wouldn't hurt to clean up all these connections and replace the charge bulb.
pmdave
There is even a resistor modification that will keep the exciter voltage going to the rotor should the bulb fail.

Kurt in S.A.

[The_Veg]

One thing I just remembered: if you are going to install an Omega kit, before doing so you should check all the crimps on the supplied wires. While the Omega wiring is generally much sturdier and better-made than the stock BMW wiring, I found out the hard way that not all the crimps were up to par. Last October (after a year with the Omega and just when I thought I could really trust it) I had a charging problem on a trip that made me have to disconnect the headlamp (PITA with the S-fairing!) and buy another battery from an auto-parts store in the small town I was able to reach before the ignition ran out of juice to run total-loss to my destination, which luckily was a gathering of fellow airhead enthusiasts. We found that the big red wire from the starter to the diode board had fried itself, and a loose crimp appeared to be the culprit. We made a new wire and first crimped the bejeezus out of the terminals then soldered them. When I got home I tightened and soldered all other crimps in the charging system. No problems since, except for discovering that that battery I picked up on the trip puked acid all over the bike's silencer, making nice stains that won't polish out and being an R100R I can't exactly just find a nice used one very easily. But that's another story...

[jblamey]

Thanks again for all your help.

I replaced the diode board, and also the regulator just in case the diode board took it out, saved both parts, the diode board to be repaired and stuck in the toolkit box just in case, the old regulator also goes in there with it.

Gotta look for the diodes as a kit or from someplace like Digikey.

Jeff

[20774]

Does anybody have a list of the diodes used on the board? They may have changed over the years... I'd like to file that away for my /7 for "whenever"...

Kurt in S.A.

[jblamey]

Seems the discharge of the battery from when the charging system diode board failure caused the battery to be weak and then the starter failed. I have a new AGM on the way. Yikes, bad luck eh? I checked around and I found a Valeo starter down in Monument for $179. Thinking of driving down and picking it up this PM. The Bosch units look like they're in the ozone $400+ and Valeos from other sources $300+.

I think I know where the starter is located, any good web pages on starter replacement? Duh, I guess I can google it.

Jeff

[rinty]

jb:

I had a local electrical shop rebuild mine; it's no big deal. But if your bike has the starter with the glued-in pieces, you may want to upgrade it. It's under the (alloy?) cover on top of the engine. There's a good article on starters by Matt Parkhouse (I think it's Matt's) in a recent issue of the MOA News.

At the risk of sounding like a broken record, don't forget to disconnect the ground before you start.

Rinty

[jblamey]

I bought a new valeo starter from Euro Motoelectrics ($179), went down to Monument, CO to pick it up, met the owner Mr. Rayski, great guy, threw in a set of plugs for free! 719-487-9397 He's got motors, and a great deal on the 400 watt charging system for the Airhead.

Put in the starter, works great, what a pain to get at tho. I took a look at the motor section of the starter and found three of the magnets loose, no wonder it was broken. I may check out the Saturn starter from the junkyard for a donor motor, so I have a spare starter just in case. BTW: The valeo EM sells has metal keepers between the magnets to keep them from shifting in place.

So I went back to check out the charging system just because I had my suspicions something wasn't right and found no output at the battery. Ouch will this not end? I removed the ground, opened the front cover, and did some more checks with the ground restored. The rotor is getting exciter voltage however when I check the stator windings I was getting residual,<2V. YIKES. Shut off the bike and checked out the rotor now reads like 4Mohms, open rotor! A few phone calls will get me a new one plus the tool. Man, what a way to get to know a new vehicle!!! I still need to put a new tire on the back but that has been ordered and will be here in a day or two.

[rinty]

What a pain to get at though...

The starter nose bolt design is compliments of the BMW Irritation Committee. Isn't that fun to put in? I understand the trick is to put some grease in a socket to hold the bolt head secure, and then thread it through the hole at the front of the engine. But I didn't know that when I did mine....

But to be fair, the starter access difficulty is more than offset by the ease of access to the valves, heads and cylinder barrels. And the alternator's easy to get at too.

Now you know why you got such a great deal on the bike, jb.

Rinty