Boxerworks.com

Hello gentlemen,

Long time, no post.

it's been an interesting few years, had bypass surgery, got married, had a decent business that is struggling due to overall conditions, but I'm happy and I have a rebuilt heart that should last a while longer.

But anyhow, i have been trying to get the bike ('78 R100/7) on the road, added a second disc, solved the leaky undertank master cylinder issue (fingers crossed) and a few other things, but I would like some verification on my charging system diagnosis, if I may ask for help.

New battery, had the bike out last weekend and was going to take it out Monday AM when the starter sounded sluggish, horn wouldn't blow etc. Checked voltage at battery and it was down to 11.9v. Put it on the charger, and when I got back all was good. Then I decided to check the charging system.

At 4000 RPM i was getting 13.2v across the battery terminals
16.7v across the B+ to D- on the diode board and alternator, respectively
11.7v at the disconnected D+ on the voltage regulator to negative on battery

Haynes says a difference of more than 4?v and there is a problem with the diode board.
I pulled the board, most of the terminals were pretty corroded from the old leak in the M/C. Hoping that that's all it was, I cleaned them,checked the diode board (OK) and made up new leads from the alternator to the board. Made all the connections and rechecked.

@4000 RPM, 13.6 across the battery
16v across B+ to D-
12v at D+ to battery at the voltage regulator lead.

I added a test lead from the other D+ on the rear of the board, reconnected again and got 13 4v from the test lead to battery negative.

That's where I sit now as I had to go make a pickup at the airport.

i am going to connect the test lead to the VR and see how that reads and maybe improves charging voltage, I would really like to see 14+v across the battery terminals. The VR is a solid state one from Motorrad if I recall correctly.

Did you resolder the connections on the diode board? I would resolder every point on the boards where the components touch the runs. If the board has single sided runs, with no through hole plating which adds strength, they may crack due to vibration.

Make sure that your test leads touch the battery terminals, not just the connectors. As you know, that is way too low and won't keep the battery charged. Did you leave it on @4000 rpm for awhile to see the voltage when it stopped rising? It will slowly creep upwards to some terminal amount. That is the charge voltage.

Our experience was that anything under 14 v wouldn't work. We seldom set them lower than 14.2 v and that was only on touring bikes. We would set them as high as 14.35 v on around town bikes.

as far as resoldering the board, how does one get through that gray paint or whatever it is on the board? I have another board, actually two if i count the parts bike, and I will try those if I need to .

And yes, I was clamped to the terminals and the Voltmeter had stabilized at the listed values.

I'll keep plugging...

My biggest question is whether that 16.7v reading at B+ is way off. Anything i've read says it should be 13.5 -14.2v. Does this indicate a bad board?

Sounds like the regulator is shot to me.