Hi all,

An update:
I got my el cheapo voltmeter from Ali, hooked it up and it works.
It shows a 0.2V difference compared to my voltmeter, so at least one of them is not correct.
But since I'm more interested in the course of the volt changes rather than the absolute value, it doesn't worry me.
The voltmeter is installed so that it is only switched on with the ignition switched on.

Here are the measurements.
First is hooked up to my Optimate 3 trickle charger. Battery fully charged.
13.5-13.4 ignition on, very slowly going down
13.2 first lights on, sorry don't know the correct name for it. The first position on the light switch, so "below" the low beam. It's only 5W.
12.8-12.4 lights on, immediately jumps to 12.8V then goes down, slowly.
11.8-11.5 high beam on, immediately jumps to 11.8V then goes down, slowly.
11.8 high beam off
12.1-12.4 lights off, jumps to 12.1V then slowly goes up.
All this without the engine running, and the battery hooked up to the trickle charger.
After this the trickle charger indicates a fault. Unplugging and plugging in again, starts the charger again.

The next day I roll the bike outside to do the same measurements but now with the engine running. So starting point for the battery is the same: fully charged.
13.6-13.5 ignition on
12.9-13.0 after start of engine @3000rpm
12.1 lights on, low beam
11.7 high beam on
12.1 high beam off
12.1-12.7 lights off, voltage slowly starts to increase, approx 15s
12.1-11.5 lights on, low beam
12.3-12.5 lights off

Got the bike in 2003 or 2004 with a new battery. That lasted pretty long (2014?).
Then replaced it with a cheap nameless brand, lasted for one year.
Another new one in, also nameless. Didn't last 6 months, got refund. Then got a Bosch, which is currently still in use (just under 3 years old).
All batteries have always been on a trickle charger during the hibernation.

I'm not an electrical expert but here's my theory.
Battery is shot, needs replacing;
RR is shot, needs replacing;
Generator is the actual culprit. This is somehow malfunctioning, which in turn fries the RR, which in turn cooks the battery.
I think this is the case since when I installed the new cheap RR, voltage immediately went up to 13.5V. Now it isn't. So I have to assume it's gone.

If my theory is wrong or if it's correct please let me know. I'm curious what you are thinking.

Greetz,
Roger

Results read as not enough charge voltage, have you tried connecting RR output directly across the battery. Battery requires approx. 14v to fully charge, slow running, lots of headlights on and less than 13v slowly degrades the battery capacity if there is no extended period of 14v running. Direct connection of RR to battery removes the wiring loom common earth loop, and should boost the charging voltage. If you decide to use the direct connection a permanent fitment, make sure you include a 30A fuse in the wiring.

Hi magg,

Thanks for the reply. It's definitely not charging.
Took the bike for a spin today (15km?).
Fully charged battery, 12.5V after starting the engine. Turning on the headlights (on high beam), reduces that to 12.2V.
As the km pile up, the volts go steadily down.
At 11.2V I take the bike up to 12.000rpm, voltage drops to 10.0V
As the revs come down, voltages recovers back to 11V.

If I turn off the lights, the voltage goes back up to 11.6 and from there on continuous to decrease.
Turning the lights back on at 11V (only 2km from home), I make it home @8.8V.
The good news is the bike didn't cut out on me. But I reckon it wasn't far off.

I measured the wiring from the RR to the battery and it had 0 Ohm resistance.
The output of the RR (measured directly at the RR), was 13.5V. At least it was when I first plugged it in.
At that point voltage over the battery was also 13.5V, so that seemed to work fine.
Now it doesn't anymore.

I'll start looking for new generator, RR and battery.

Greetz,
Roger

Disconnect the plug at the RR. Use multimeter on resistance range and place one probe on any yellow wire at the plug and the other on the chassis. Should measure infinite resistance. Place one probe on yellow at plug and other on another yellow wire, should measure less than 2 ohm resistance. Repeat this procedure on all three yellow wires.

Hi magg,

Thanks for the reply. I already did that and the readings were infinite between any three of the yellow wires and chassis. 0.1 Ohm between the yellow wires themselves.
Also with the engine running I get 30V @2000 and this goes up to 42V @4000 on the yellow wires themselves, so that seems to be working.
Nevertheless I have a problem.
My guess is that it is not a constant problem but maybe it only pops up when heated or something like that.
I think I'll just change all three components.

Thanks,
Roger

Not sure from your comments, did you replace the connectors between the alternator output and the loom, what was the condition of the connector at the RR?

Hi Magg,

The condition is relatively good. After all it's a 25 year old bike. That means the plastic of the connector isn't exactly white any more but a bit faded yellowish. The contacts themselves are clean, not corroded. All measurements check out.
So today I got a second hand RR from an FZS600. Bigger unit with cooling fins.
Different connector but made some adapter cables.
Remeasured the cables and generator, everything still checks out.
Hooked up the new RR, started the bike and guess what: 13.8-14V on my now installed voltmeter. So it's charging!
I now have to mount the RR (slightly different mounting holes), tidy up the cables and I'm back in business

Thanks for all the help guys. Seeing the examples of bad wiring and connectors really helped me finding the root cause.

Greetz,
Roger