Charging system issue

[Ceeby-jeebies]

My 78 400f2 model seems to have a charging system problem and I can’t get to the bottom of it. I had a series of problems in which the battery was unable to start the bike after or during a run and also appeared totally dead at home one morning when it had been fine the day before. A multimeter showed 12.4, 12.5V at the battery when the engine was running regardless of the revs. It should be 14.5 to 15V when revving to 3000 and beyond according to Haynes.
- Subsequently I put in a new battery but after one check when it was charging correctly at about 14.5V at 3000 revs, it reverted a few days later to 12.4V, or 12.2V with the headlight on
- the multimeter showed the rectifier was ok as was the generator.
- Unable to check the regulator so I replaced it and the old rectifier today with a combined regulator/rectifier from David Silver. But the problem remains with the battery only being charged at 12.4V
- the only other oddity is that the electrics twice were completely dead (no ignition lights when I switched on).The fuses appear ok. I prised apart the ignition switch connector and cleaned it with a brass brush, and everything came back on again.
Any ideas gratefully received

[McCabe-Thiele (Ted)]

What type of battery have you now fitted & when fully charged what is the voltage at the terminals I would expect it to be around 12.85 volts or more?

Are all your earth connections good from battery to frame etc - check the headlamp earths. 

Have you checked the alternator connections to the wiring loom.

Have you cleaned the fuse holder - have you checked the voltage at the fuses when the ignition is on?

There are some tests you can do to check the field windings but that's beyond my knowledge.

[Ceeby-jeebies]

It’s an AGM battery replacing a MotoBatt AGM battery, both of right size and spec. Fully charged giving 12.7v, 12.8v.
Earth connection from battery ok, but have not checked headlamp earth.
Alternator connections prised apart, cleaned and reconnected after diodes tested ok on multimeter
Fuse holder ok but have not checked voltage there - will do
Thanks so far!

[K2-K6]

As Ted mentioned, have you checked security/integrity of wires to and from alternator?  If these are not consistent you'll have no output to regulate or rectify.

[Oddjob]

I'd especially check the 2 bullet connectors from the stator, tend to get corroded due to location. Also have a look at the 3 yellows going onto the field coil, reports of them detaching and just one loose would really lower the output.

[Ceeby-jeebies]

Have checked earth connections, alternator connections, fuse box, bullets etc and all seem good. Problem persists sadly.

[Bryanj]

Have you checked the stator coil resistances between yellow wires, i have had one that had something dropped on it and cut a winding

[Matt_Harrington]

Maybe this thread may help? http://www.sohc.co.uk/index.php?topic=16291.0
Matt

[Cappodimonte]

Aside from checking and cleaning the bullet connectors check the wire soldered to them, if it has a green tinge suspect it to be causing your problem as it will have high resistance. All the earth points need checking, including the one under the petrol tank which is usually overlooked as it is unseen for the most part

[Ceeby-jeebies]

Thanks for all the suggestions. Tried everything and cleaned everything and put it all back together again, and now it’s charging better if not as per the manual, ie 12.5-12.6V at tickover and 13.3V-13.5V at 2000-4000 revs. Any more revs and the multimeter seemed to go erratic, flickering on and off with no clear reading!

[Bryanj]

That probably means thr contacts in the reg are vibrating between zero and either halh or full charge.
There is a document, in alladins cave i think, called 3 phase charging which explains with diagrams how the system works

[Ceeby-jeebies]

Thanks although it is a brand new regulator rectifier from David Silver that I fitted on Thursday

[Bryanj]

Never liked the electronic versions personally, too fragile for me

[Oddjob]

Have you tried another field coil or stator coil? Just to see if the fault goes away, sometimes swapping parts is quicker than fault finding.

[Ceeby-jeebies]

Turned out to be a loose stator wire. Now fine when soldered back in. Thanks to all