No Charges and a Lack of Evidence - an Electrical Mystery

Clive said:

Greetings All. Here's one for the Auto Electricians;
I've been involved with various fields of electronics both hobby and job for many years but this is puzzling me. Haven't started pulling the bike apart yet so looking for inspiration before I start. A 2017 961CR Euro4 Donny Bonny.

Bike has been running really well for years since the 'Saviour of the 961' Stu carried out a rebuild. Rode to work but at the end of the day just the clack-clack of a low battery. Left it there over the weekend and put it on charge all day Monday. Started first press. Half hour ride to my son's house and the voltage was hovering at 12.2-11.9. That didn't look right. Switched it off but then no power to start it. Charged it and rode it home. Again the voltage slowly dropped; obviously not charging. Not good.

Unplugged regulator - interestingly completely unbranded...... Measured coil resistance and hurrah! coils seem intact. Strangely all resistance across the regulator terminals was almost infinite, but not a particularly meaningful test. The positive on the connector goes straight to the battery and is showing 12v ish with the negative terminal or engine case as ground. Didn't know if there was a fuse in the way which had blown but a check on the circuit diagram showed a straight connection. So a new MOSFET regulator was ordered. Supposed to be kinder for the generator coils and anything with MOSFETs has to be good

Now here's the interesting bit;

Bolted Reg. straight on and went out for a celebratory ride but....... no charging. Oh dear. Unplugged regulator and grabbed old multimeter. Generator coils not open-circuit. Voltage on terminals to battery a bit low at 8 volts but there is voltage. Measured voltage on charging connector just out of curiosity and, hang on, that measures 12v ish. My mistake so tried again and sure enough voltage on positive regulator connector is lower than charging connector positive (to connector or chassis earth both same so no earthing issues). Scratch head.

Grabbed proper Fluke digital multimeter and repeated. This time both voltages the same. Repeated with old multimeter and different voltages....... Ahhh we may have a clue at last. So reckoned the lower impedance of the analogue multimeter is dragging the voltage down on the Reg connector. So measured impedance from Reg connector positive to charge connector positive and we have 4k Ohm!!!!!! That fits with the two multimeter readings, the apparently good coils, new Reg but no charging.

Now there should be no fuse assembly in the way according to the diagram and if there is a bad/loose connection it will normally only drop voltage under load so it doesn't really fit with a loose/bad connector. A 4k resistance would normally indicate a path through some other bit of circuitry which is bridging between the connector positive and the battery. But nothing on the circuit diagram looks obvious. Of course we don't know how the loom is wired and if there is a peculiarity there.

In the middle of a house move so haven't started stripping the bike yet. I could just wire directly from the Reg connector to the battery or even to an external battery to see if it charges it but thought I'd lob this one in to see if some bright spark (see what I did there?) has an idea. Otherwise fit a trailer with a generator and Optimate....?

PS after 9 years (WOW where did those go?) just love riding this bike. How it rides, how it sounds, how it looks. Wish it was a few pounds lighter but it probably thinks that about me..... Can't think of anything I'd want to replace it with.

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Clive said:

In the best crime drama tradition never dismiss something which doesn't seem quite right; my tracker has not updated for a month???? Maybe it has both switched and unswitched + connections and that 4k resistance is through that and the regulator + to battery has gone O/C?

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cliffa said:

@Clive Have you checked the regulator fuse near the battery?

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Clive said:

I'm so surprised at you cliffa, as you are such a knowledgeable log-term member; if you look at the circuit diagram there is no regulator fuse! And the circuit diagram isn't going to be wrong is it?

For the benefit of some of our overseas Forum friends this is what we call 'sarcasm'.

It has to be a hidden secret fuse (those horrible under-tank fuses) or a broken connector based on the symptoms.

When back from shops will take a look. And fit new battery as preventative maintenance.

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