550F charge issue?

[Davelu88]

Hi all , when checking over my bike I tested the battery with my multi meter, the battery was 11.84v with the bike off . With it switched on it dropped to 11.45v and with it started and revving it rose to 11.49v . I put the battery on my other F1 and when revved it rose to nearly 12.8 v . Does anyone think I have a charging issue 🤔

[Sesman]

Yes, absolutely.

[Davelu88]

Any ideas on what to check first, bearing in mind that I am electrical challenged although I can swap out some parts from my other one to check , eg rectifier etc .

[Sesman]

Obviously carry out a visual check of all connections and joints, especially earth connections. You can check the alternator with your multimeter set on AC. Suggest you have a peep in Aladdin’s cave at the workshop manual….excellent guide in there. And yes of course, swapping out components is a quick dodge.

[Sesman]

Manual page 94….

[Davelu88]

Many thanks

[McCabe-Thiele (Ted)]

Personally I would start by charging the battery fully with a charger then see what the volt readings are after standing overnight Then I would see what the readings are with the engine running. Could be you have already done this. When I've ruled out the battery then as has been said I would check earth's etc & charging voltage. I use an old fashioned clip on induction gauge on the battery earth strap  to then check current flows.

[Davelu88]

Thanks Ted ,  Battery is on charge so will see what happens but same Battery on other bike showed charging when revved . I asked Mick the previous owner and  he said he checked it when rebuilding it and it was putting out 14v so obviously something amiss . Electrics are like magic to me so not overly confident with this 😒

[deltarider]

Personally I would start by charging the battery fully with a charger then see what the volt readings are after standing overnight Then I would see what the readings are with the engine running. Could be you have already done this. When I've ruled out the battery then as has been said I would check earth's etc & charging voltage. [...]

This ^. After a night at rest the battery, not connected, should read 12,6 V or more. When less, battery is nearing its end.
Start engine with fully charged battery. Switch on the headlight. Rev the engine from idle to say 3500 rpm, whilst holding your left hand in front of the headlamp and check if the light's intensity increases. When it does, there is charging. These are basic tests. Toying with the multimeter comes later... maybe.

[K2-K6]

Regardless of battery float level, it should be showing decent increase in charge volts when running and revs increased. 

Going from 11.45 to 11.49 when revved shows there's negligible power coming from alternator to battery, for whatever reason that may be.

That's the problem to investigate. Basic connection check first, wires from alternator, everything around regulator rectifier to ensure no simple disconnect is present is initially a good place to start.

[Sesman]

Like i mentioned, visual/physical check of all connections especially the rectifier and regulator ground/earth. If you intend to substitute devices from a donor I’d start with the regulator (field control) then the rectifier.

Most likely problem is a poor ground/earth for either the field coil, regulator or rectifier.

[McCabe-Thiele (Ted)]

Not sure what impact a failing battery has on the  voltage output but below is a little account of a battery failing in a car.

In 1974 I was taking a prospective buyer for a test drive in a brand new red Opel Ascona in Burton on Trent, I was held up at a set of temporary traffic lights on Balaclava Road opposite the Shell Station. As I started to move off when the lights changed to green the engine started to loose power it stalled - I saw smoke coming from under the bonnet edges so switched off the ignition and we alighted from the vehicle.

Vehicle was towed back to base and the battery had failed due to a dead cell short. New battery fitted & everything was okay - customer decided to buy an Audi 100 from me instead!

[K2-K6]

Yes Ted, a dead short is always going to be problematic  as there's quite a potent energy stored in there to make fire with  it's usually the result of physical damage though to get that.

If you loose one cell it tends to be below eleven volts (missing two from 12.6 gives 10.6) is a good indicator.  In the eleven range, they're usually OK but can be toward end of life or just reasonably discharged from not have alternator input.

[deltarider]

Here's a little anecdote about how to make it home with a dead battery. Enjoy. http://forums.sohc4.net/index.php/topic,164389.msg1914136.html#msg1914136

[McCabe-Thiele (Ted)]

Back in the late 1969/70 I had a battery fail on my Honda 250 Dream - at that time the only option was to buy one from a Honda dealer iirc it was £34.00 (3 weeks wages) for a  replacement.

I cut around the top of the battery to separate the top section from the casing - pulled out the top - a load of what looked like thin sheets of glass fibre started to fall out from between the battery plates. I pulled them out & binned them washed out the sediment in the bottom as well as dipping the top with the plates attached into some clean water. I Araldited the top back on and filled with battery acid & put it on trickle charge overnight.

Incredibly the bike started first touch of the button, when I sold it six months later to a mate - I told him to never let it go flat - about six months later he let it go flat so had to fork out for a new battery.