A strange electrical problem.

[Barry]

Do you know if the alternator can raise it's output voltage and not charge ?

No, if the alternator voltage is higher than the battery voltage then a charging current must flow.

The normal behavior of the alternator is for the voltage to fall slightly as the engine warms up.  Say it's charging at 13.7 Volts with a cold engine by the the end of the ride it will have fallen to something like 13.4 -13.5 volts. It should still charge though as the technical reason for this voltage slope being built into the voltage regulator is that it's designed to compensate for the batteries internal resistance falling with rising temperature which makes it "easier" to charge.

Could it be that the 0.6 amp current drain only occurs with a hot engine ?

[georgesgiralt]

So, here are the day's results :
As said, no start at noon. The bike had to be pushed to start. So I rode the Honda to return to work.
When out, I came home and measured the leaking current on the R65. 0,1 mA max. (oscillating from 0,01 to 0.1 mA seems the clock does not draw constant current). Battery was around 12.50V. (I rode without headlight at noon and with engine revving). Started the bike and measured the alternator voltage : 14.25 V with only the engine and 13.9V with the headlight both at around 2000 RPM. I checked the residual alternating voltage (just in cas I had an intermittent diode) and the voltmeter gave me less than 0.5V which is not so bad..
Bike started instantly. So I went to the battery shop and bought a FIAMM VRLA (looks like the Tashima AGM battery I once had). Returned home with the new battery in the pannier and with the old running fine.
At the battery dealer we measured the leak : 0.0 A and the current draw of the starter. There was a peak at 300A (which is not uncommon for a Bosch). The guy was very reluctant to sell me a new battery seeing the ease the old one started the bike... As I need to be sure I can depend on the bike I invested...
I'll order a starter relay from BMW just to be sure.
I do hope I will have a trouble free bike now ....
Will keep you posted ;-)

[tvrla]

Three hundred amps is a LOT! Mine don't usually draw more than 100 to 150. I think the starter is your problem.

Try the new battery (since you have it) and see what happens.

There was a thread on Adventure Rider several years back that went for pages and pages and pages -- trying to figure out this one particular bike's electrical problem. It didn't seem like a battery issue at all, but finally out of frustration it was replaced and that fixed the bike!

After that, anytime someone presented an electrical issue the stock answer was "it's the BATTERY!".

So I'm saying, it sure sounds like the starter at this point, but who knows? I will say, that if the battery could flow 300 amps to the starter, it doesn't seem to be too bad off. Perhaps the answer is that the starter draws sooooo much current that the ride to work doesn't recharge it sufficiently to offer up another 300 amps at lunch.

[georgesgiralt]

Hello Wirespokes,
I said that the peak current was 300A when starting not that the starter used that for a long time. It needs around 160 A but the surge starting current is 300A. No battery of this size could sustain such a current for a second or more  IMHO.
Monday evening I put the AGM battery on the tender to get it charged. Tuesday morning starting was fine. Ditto at lunch or in the evening. This morning starting was fine... So I save the current for the Optimate .... Will see at noon or tonight ...
I wonder if the old battery has a bit of lead moving inside which could explain why it is fine some times and not at other times. But this still don't explain the leak seen by the battery guy once...
So, for now it seems to be fixed. Wait and see .

[Barry]

I too initially thought the 300A was high. The 300A surge current if very brief is probably normal though as it's a characteristic of electric motors that they have a current peak while they get up to speed. The specification for our Bosch starter lists a stall current of 320A

[georgesgiralt]

Hello !
At noon, bike started like new ! I had to buy something to eat and bread. 2 stops so two more starts... 5 minutes apart. A breeze !
Back to work, without any problem. Tonight, everything was fine. In the garage, my Chinese multimeter reads 12.96 V just after I've stopped the machine.
So glad I drained gearbox and motor oil and changed filter. Put new oil in the gearbox and in the engine. Started the bike to check oiling and leaks. Still running fine.  
I'm confident the problem is solved or near it !  8-)

[montmil]

Cool. Fingers crossed for ya.

[Bob_Roller]

Glad to hear the fix was quick and not overly costly .

[tvrla]

So, again, it was the battery.

Isn't it amazing how often a bad battery confuses us into thinking it's something else and CAN'T be the battery?

[georgesgiralt]

Well, I still don't know if the bad battery was the root cause or the consequence !
The battery guy measured 600 mA drain current with it's tool.
I was unable to find why and where this drain came from but it may still be present. Time will tell.
BTW, bike started fine this morning.... but oil filter leaked so she is in the garage 'til tonight ... I'll fix it ...

[steven m]

Is it possible that when you ride the bike in the morning and then park it you are leaving the ignition in the second position, the one that leaves the parking light on?  Or that your voltmeter is drawing current all the time?  I put a Wudo 90S fairing on my bike with a clock and voltmeter, using the factory harness, and the battery seemed to drain overnight.  Took it off and the problem stopped.  Not a lot of room under that ignition switch for all the connectors.  On my 83 US spec R65, when the bars are fully turned to the left, the turn signal switch hits the tank bag just enough to turn it on, and that will drain the battery.  You might try systematically unplugging lights, one at a time, to see if you can isolate the drain.  I think if the alternator wasn't charging you would have a red light on.  Could be as simple as a multi pin connector loose or corroded.  A wire to one of my turn indicators wore through the insulation and was grounding to the mount.  After a while, the fuse would blow, but not instantly, which was irritating.  After I found the fault it was so obvious.
Electrical gremilns are maddening...

[georgesgiralt]

No cabling problem nor parking light left on.
As far as I can tell it is a battery problem. With the new battery everything is fine. As per the 600 mA found at the battery dealer, a friend proficient in electronics and measuring devices told me that "using a 300 A meter without contact to measure a so small current is doomed from the start".
So .... I ride, I smile and try to forget the 72 € I left in the pocket of the battery seller ...

[georgesgiralt]

Hello Lads,
The day before yesterday I put the old battery in charge. When done, I let it sit for the night and measured the voltage. According to the chart I've, it has lost 10 % charge sitting on the bench.
Yesterday it was 15 % and today 20 %.
The bike runs fine and start every time with the new AGM battery .... All is well !