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I’m having a charging problem with my ’94 R100GS PD that has resisted my best efforts at troubleshooting. The charging light does not come on while running (but does light with the ignition switch) but I’m getting extremely low charging at the battery. After some cursory examination, I decided to start out with a new battery as the old one came with the bike and was of unknown age.

This had no effect so I bypassed the voltage regulator with a jumper and still got low charging voltages ( ~11.5v @ 3750, ~10v @ 2000rpm).

I then pulled the front cover and found an Emerald Island diode board (which fit the previous owner’s claim of a new diode board last year) mounted on degraded rubber mounts. It appeared to be held in place but came off (all 4 mounts separated) in my hand when I touched it. I replaced the rubber mounts with metal ones and examined the board, finding the “U” wire not soldered at the board end (it pulled free of the spade connector which, oddly, was soldered to the board). I soldered the wire into its connector and, thinking my problem found, put it all back together. No such luck, still charging low.

I then checked the rotor resistance and got 3.9 -4.1 ohms, depending where on the rings I put the probes. This fit the values in my manual.

I moved on to the stator and checked resistance between the three windings (~9 ohms consistently) and between each and ground (open circuit) which all met with what I’d expect from a healthy stator.
At this point, I backtracked to the diode board and began working through checking the diodes. Unfortunately, I wasn’t able to find a good explanation of how to troubleshoot one of these boards. I used the table on Joerg Hau’s site (http://jhau.maliwi.de/mot/r-elec.html#alternator1) to test as much as I could but there is no “B+” terminal indicated on this board. The values I got from this (minus the absent “B+” set) all seem to match Joerg’s table.

I’m at a loss and am on the verge of resulting to mindless parts replacement as everything acts like it should work and the bike has run well for 8,000+ miles since I bought it in may. Can anyone offer advice on some flaw I may have missed?

Thanks!
Clark

Hmmm,

Voltages of 10 and 11.5 volts at running speed should only be related to the word 'charge' when it is accompanied by the words 'lack of'... or to put it another way, your alternator isn't producing any useful charge at all.

I'm not familiar with the Emerald Island diode board but I think it must have a B+ terminal somewhere as B+ is the voltage aoutput to the battery. I assume that there is a connection somewhere from the board to the battery and this is the B+ terminal.

Reading through your post, I think its highly likely that the problem is in the vicinity of the diode board. There is one thing worth checking and that is the board earth (ground). This needs to be clean and making a good connection. As much current runs through this connection as runs though the big wire to the battery (more in fact).

If this give no results, then I think you are looking at a replacement diode board.

Rob

Rob,
Thanks for your thoughts. By the time I noticed the problem, the resting battery charge was at ~8v so I took 10+v as an indication that there was some, albeit insufficient, alternator output. I just replaced the diode board and voltage regulator with Thunderchild units to no effect. Now I'm wondering if a (1 of the 3) stator winding would account for the reduced (by about 1/3 of expected) charging voltage?
Clark

Before chasing any more "problems", I would run a ground wire from the diode board mount straight to the ground lug on the frame and continuing back to the battery ground post - per Rob Frankham's web page. I know from personal exasperation that the black coating on the timing case is a pretty effective insulator.

BRUSHES????
Resting Bat voltage of 8v is mighty low.
How does it look after charging with an external charger?

Apologies that I've not been back before this... I've just had a horrible thought... what are you using to measure your voltages...?

If you're relying on the stock voltmeter then go out and invest in a digital multimeter before you do anything else. You can get a cheap (but adequate) one from most auto stores or electronic parts retailers for a very small sum. The stock voltmeters are notoriously unreliable.

The reason I say this is that a lead acid battery with a no drain/of charge voltage of 8v is essentially totally flat. There is no way that it should even light the bulbs. To put it another way, if the battery is even trying to start the bike, I would be pretty sure that there is something wrong with your reading.

It may just be that there is nothing wrong with your charge system at all.

Rob

I was just waiting to find out how a battery with only 8 v at rest could start the bike.
Only Rob noticed THAT...

Jean, I think it's pretty evident that it wouldn't.

Others,
Thanks for your input. I installed an Omega 450 system and it resolved my charging issue. If you're on the fence about one of these, I really recommend going for it. It was a super easy install and the support and customer service we're top notch.

Optima 450...one of these?

http://www.nitroplanes.com/75m37-optima ... 050kv.html

...or do you mean "Omega" 450???

Kurt in S.A.

Kurt, You're right. The bike got an Omega system and my truck got an Optima battery. My life involves far too many expensive electrical parts lately...