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Evening and sorry if this is a dumb question as a first on on the forum.

I have a 1986 R80 and have had no issues with the charging until a ride today, which has me confused.
Did about 25 miles and then pulled over for a photo, when to restart the bike and there wasn't enough to start it so 2nd gear bump and off I go thinking "ill do the 30 miles home and look at it later". Did about 15 miles more then the bike started miss, lose power and I came to a stop. Battery appeared dead, nothing and unable to bump it. Just had enough power to light the side light and that was it.

After 20 mins or so sat trying to think of how to get home I switched the ignition on again and there was a tiny bit of power at the button but nothing near enough to turn it over, but it did allow me to bump it again and to my suprise it got me home another 15 miles. When I got back it restarted as normal on the button and I had a headlight and about 11.5v on the battery.

I took off the front cover and cleaned all the connections on the alternator and electrical cleaner on all the terminals, cleaned the brass coloured rotors and the brushes look ok. Restarted the bike and with revs up and a multimeter across the battery it rises from 11.5 to just about 13v.

I have got the battery on charge overnight and will retry again tomorrow to see if I get a higher reading .

Question - what should you get with the multi meter across the battery with revs raised and a fully charged battery .. 13, 14, 15?
Highest I have seen when getting the bike back on the a year ago was just over 13v but its started and run with no issues until today.

Cheers

Welcome! 9 times out of 10, the problem is the battery. Even if it charges, you should probably remove it and get it load tested at a local store. If the battery is a sealed type, they can just be OK and then drop off a cliff.

When taking the front cover off, always remove the grounds to the battery...it's possible to short out sensitive electronics under there.

When revving the bike to say 3K-4K RPM, you should see a solid 14v. If you've only been getting 13v, then the battery has not been getting fully charged. Hopefully you'll be lucky with a solid charge with an external charger.

A final thing, be sure and confirm that the ground connection to the frame is clean and solid. Don't over tighten that connection, but it needs to be snug.

Kurt

Thanks for the replies.
I didnt know that about the earthing point in the trans and will check that. I don't have a charging light as it's yet another "messed with" old RT and I replaced the light with a diode in the wiring to replicate the bulb after lots of reading and learning a couple of years ago. I fitted small LEDs and then wondered why it wasn't charging! It's worked fine up until yesterday and clearly was charging once back on the road. The only other thing I forgot to mention is one side of the gel battery does appear to have got hot. I wondered if the diode board going bad could cause it to overheat to where it stopped working and then as it cooled it was able to be bumped again?

Read this and is an R80 regulator which I'm guessing is under the tank a "shunt regulator" which i believe is also know by another name I can't remember and maybe the problem..."Shunt regulator burnout: If the shunt regulator burns out, the regulator rectifier can't control voltage levels, which can cause the battery to overcharge.

Daft as it sounds I quite like it when stuff like this crops up as you end up learning stuff about the bike, how it works, how stuff like AC/DC differs and a big reason why I lost all interest in modern bikes and went old again where half the fun is the fixing and maintaining it.

So after cleaning everything up yesterday and charging battery overnight I have 12.5v and then on revving the engine 13.5 to 13.7.

Will take it for a run on next days off and see what happens. Whether there's still a problem or was it just a simple clean of terminals and brushes

Are you measuring battery voltage with your own known-good meter? There can be a drop in voltage if you're looking at a factory installed gage somewhere.

Also, you could be having some voltage drops along the full path of battery charging. All of the corrosion that builds up at each connection adds to the loses.

Kurt

Yeah just using a multi meter across the battery terminals.
Going to see what happens in a few day when I take it out and do 50 miles.

Airheads don't use shunt regulators. Instead the VR is in series with the rotor winding and varies the average current through rotor to maintain the required charging voltage which for a standard VR is 14 volts. As you have found, the measured charging voltage will vary depending on the state of charge of the battery and you will only expect to see the full 14 volts with a fully charged battery and no heavy electrical loads switched on.

Your battery sounds suspect. A standard Gel battery doesn't like excessive charging voltages but it doesn't sound like yours has been seeing even the full 14 volts so why did it get hot ?

Thanks, and yeah doesn't really make sense. I thought it had got hot as on one side I had some lightly packed sort of nylon packing stuff and that had melted against it, needless to say I've taken that out now