15 minutes ago I got the battery charging circuit working on the R65, I have spent a total of 12 and a half hours on this, the only break being a 1.5 hour diversions to put the wife's bike back together after borrowing some bits.
I could not work out what was going wrong. A Bosch alternator is not rocket science, consisting of:-
A soft iron rotor with a coil wound into it so that excitation current will increase its magnetism and therefore the amount of power produced;
A pair of carbon brushes to impart excitation current to the rotor
A "wye" or "delta" wound stator coil in 3 part harmony.
A voltage regulator.
A bank of diodes to turn the AC power produced from all of the above into DC power that can be used to charge batteries etc.
and lastly, about 1/2 doz bits of wire that connect the major assemblies, stator, regulator and diode board together.
So simple as, but mine didn't work.
Lunch time Saturday I did the obvious, separate out all the individual components and test them individually (where possible). Long story short, everything tested fine and dandy, but it still didn't work.
The rotor (which is always the primary suspect because it is the only bit that "moves') tested just fine, besides I had a "gen failure" light which will not work unless current is passing through the regulator and the brushes and the rotor. The regulator is a brand new purchase, so I grabbed a spare and fitted it - no charge. Ok that left the stator and the diodes.
Tested the stator, it was just fine. Tested the diode board and it came up with the right numbers, although a couple of times it seemed to take a long time to settle at the correct resistance, but the final figures were OK, so not the diode board.
Lastly I rechecked the wiring, no problem found. I did notice that the three phases were wired up in a different order to the wife's bike, I couldn't see that would make any difference, but i changed them anyway - no charge.
Then I remembered something critically important.
The alternator in the wife's R80 is actually out of the R65, I dimly remembered battling with her non-charging alternator and being unable to find anything wrong with it. Eventually I simply put the entire alternator, diode, regulator, wiring package out of the r65 into it and it worked - case closed, although I had a vague memory of being suspicious of the wiring.
Of course I forgot all of that until I'd spent nearly 8 hours checking and re-checking stuff.
Now it occurred to me at this point that I had a fault that was "hiding" from me. It's difficult for wire to do that, it either works or it doesn't mostly (with rare exceptions), I knew it wasn't the regulator because I'd swapped it.
That left the diode board. I had a spare I'd bought along the journey of the last year, problem was it was a freebie throw in for the alternator i bought and the seller hadn't packed it well, it tested OK but the printed circuit board on the back was cracked and I really wouldn't trust it.
Which led me to pulling the diode board out of the R100.
Fitted it, cranked the engine and it started charging like a bought one.
So what is going on with the diode board I first used - which I now remember as coming off the wife's bike? I had a hunch and this time instead of mucking about with the minute current applied to the diodes by a multimeter I rigged up a test lamp consisting of an old Kombi headlight - i wired the high and low beam in parallel to maximize the load.
There are of course six diodes on the diode board, they work in pairs to rectify the current coming from the 3 phases of the stator. As soon as i loaded up the middle pair the diode went open circuit which it should not have done. I waited 5 minutes and tested that diode with the meter and it firstly gave a "funny" indication, then tested perfectly - in both forwards and reverse current. Then i hooked up the test lamp again and it failed immediately.
What a b-a-s-t-a-r-d! Tests perfectly using test equipment and fails as soon as a real world load it put on it.
I am going to keep it and give it to someone I really dislike when they need a diode board.....
Well, glad that is over, but it has nicely stuff nearly two days of working on old BMW time for me.....
Got a few other things done, will post some photos tonight.