Okay, round two. As soon as I got home from work, I did the following:
- I put the battery in after removing it from the charger. It had been charging all night/day and was at 13.44 V in the bike with the lights off, dropping down to 12.4 with the lights on. I think this is pretty normal.
- I started the bike and the battery voltage was about 12.4 V at idle (1200 rpm).
- I checked the difference between the battery voltage and the R/R voltage.
Battery voltage (negative to positive terminal): 12.4 V
Regulator red/white wire to negative battery terminal: 12.2 V
Regulator black wire to negative battery terminal: 12 V (this is the black wire that connects to the main power circuit and fuse box, not the wire to the field coil) - I did a battery voltage vs. rpm test with the field coil powered by the battery. I did this by shutting off the bike, pulling the contacts out of the connector housing, and jumpering them to the battery. Black to pos, white to negative.
12.5 V @ 3000 rpm
12.6 V @ 4000 rpm
12.8 V @ 5000 rpm
13.3 V @ 6000 rpm - I did a battery voltage vs. rpm test with the field coil powered by the regulator, with the following results:
12.4 V @ 2000 rpm
12.7 V @ 3000 rpm
12.8 V @ 4000 rpm
12.8 V @ 5000 rpm
12.9 V @ 6000 rpm
So, in the above tests, both results are similar except for the outlier of 13.3 V @ 6000 rpm with the batt. powered field coil. Not sure if that's significant.
Now, the previous owner passed on a bunch of parts with the motorcycle. Looking at these parts, and at all the snipped and resoldered connections in the wiring harness, I'm starting to wonder if he'd been troubleshooting the same issue and had given up. The battery in the bike was apparently pretty new (though I bought a newer one), he provided a spare regulator, a spare stator coil, a spare stator coil housing with brushes, and a spare regulator/rectifier, all used. Next time I'll take a close look at the bucket of spare parts when buying a bike
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The next test was to swap in the other R/R, which I had previously checked with the diode test (same results as in previous post). The results were:
- New regulator, field coil powered by regulator:
12.2 V @ 1200 rpm
12.6 V @ 2000 rpm
12.8 V @ 3000 rpm
12.9 V @ 4000 rpm
13.0 V @ 5000 rpm
13.1 V @ 6000 rpm - New regulator, field coil powered by battery:
12.3 V @ 1200 rpm
12.6 V @ 2000 rpm
12.9 V @ 3000 rpm
13.1 V @ 4000 rpm
13.1 V @ 5000 rpm
13.2 V @ 6000 rpm
So, about the same.
After this I tried checking the current that was being output (I think) by the rectifier. I hooked up an ammeter in series with the red/white wire that leaves the R/R and heads to the starter relay. I wasn't sure how to measure this (AC or DC) so I tried a few different settings. Unfortunately I didn't write much down for these tests, but I recall the following:
- DC measurements: the measured current fluctuated wildly (by several amps) at idle, and climbed as I revved the engine. It reached upwards of 14 amps, but was fluctuating wildly the whole time.
- AC measurements: the measured current was something like 0.6 A and was more steady. It seemed to decrease a little with increasing revs, until above 3 or 4000 rpm it climbed until it was at 1.1 or 1.2 A at 5-6k rpm. Again, I didn't write much down.
I also checked all of the yellow wires leaving the stator while the engine was running, with the AC measurement function. They were all the same, 10 or 12V when revving the engine around idle to 2-3 k rpm.
One final test was to recheck the difference in voltage between the battery and the regulator. Again I got more or less the same values as previously. I also checked the voltage on either the black or the white wire leading to the field coil (can't remember which) and it showed 0.6 V above GND. I'm not sure if the ~0.5 V difference between various points in a circuit is significant in a bike. As far as I know this usually implies that the conductor is under-spec'd, but perhaps that's not unusal in a bike. And all of the ground lines are AWG 16 or so, about the same as what comes out of the RR/alternator etc.
Anyway, I'm pretty confused as every individual test I've performed seems to indicate things are normal, and unless both R/Rs are failing with the same symptoms, the problem is elsewhere. Also, what is the spec for charging voltage delivered by the R/R vs. rpm? Is this published?
Is there anything else I can check? I've looked at the grounds pretty closely, and was surprised to find that the chassis ground was so far away (near the ignition coils at the front of the frame), but this sounds normal from Hondaman's book. I'm really hoping it's not something crazy like an intermittent short that shows up at a certain temperature...
Thanks again!
PS after all these tests the battery had drained to 12.1 V with the lights on... so, winding down steadily. I've got it on the charger now.
