Hi Stu, I do not have a good explanation for that. Maybe it was a lower wattage headlight bulb, ?LED. Was that 30 mph in top gear on a twin? As an aside when I had mine I fitted a small fan, similar to that which is in an electric hand drill, to the armature to try to keep it cool. It worked for several years but whether the fan did any good I do not know. My worry with all these small devices is that nothing is 100% efficient and the electrical losses will appear as heat somewhere. It is going to be interesting to see if the experiments with brushless servo motors used as generators is successful.