At about 27k miles the charging system stopped working, failing with low voltage and no fireworks. It turned out to be a grounded stator winding. Surprisingly, the stator looked absolutely perfect, and very carefully made. There was green plastic molded over the core, fabric sleeve insulation over all the winding splices and more fabric insulation cushioning the strain relief supports on the wires.

Accounts on the Web suggest stator failures like this aren't rare. So far, nobody seems to be trying very hard to figure out what's going wrong. Admittedly, it's not obvious how to figure it out.

With the new stator installed the SV seems to charge quite well, 13.7 volts on a LiFePO4 battery 3 days after a 30 mile ride.

My attempt to isolate the short in the old stator succeeded after a fashion. Gently sawing through the common point of the wye winding left one phase connected to the core, the other two still connected to each other but not to the core.

Unwinding the shorted turns from the output end with a test light hooked up got me all the way back to the center of the wye. About five turns out there was a blackened spot on the green plastic over the core. A test probe revealed bare metal amid the charring.

The mechanical integrity of the windings is impressive. Attempts to pry the splice free of the varnish, rather than cut it, were totally futile. It seems quite implausible that vibration played any role in the failure. The wires simply can't move. There may have been an air bubble at the point of failure, allowing a track to form, but the low voltage makes that hard to understand. Most insulating enamel will hold off a couple hundred volts (if it's undamaged). Probably the enamel got scratched and there was a flaw in the green plastic over the core. Any air gap must have been extremely small, less than a few thousandths of an inch.

The plastic sleeving over the output wires was brittle and cracked during disassembly. It had nothing to do with the failure, but did suggest age has taken a toll of the materials of construction.

Around a year ago I notied a fast blink on the turn signals when the revs went over about 7k. It only happened on vigorous engine braking toward the end of my exercise ride route. I checked the voltage with a simple LED bargraph voltmeter and saw no anomaly when the flasher was hyperventilating, but I couldn't reproduce the effect in the shop when a good voltmeter was handy. I chalked it up to an old flasher. Perhaps it was the stator putting hash on the harness.

For a while I harbored notions of trying to rewind the core as a spare. Seeing how well it was made and how hard it was to take apart that seems unrealistic. I'll save it as a relic and curiosity, and devoutly hope I never have a reason to attempt a rewind.

Thanks for reading,

bob prohaska