Originally Posted by
zacster
What I want to do is to take my DVM with me and just measure what the dynamo puts out unloaded, and also what the light draws. There is the connector for the rear light that I could tap into, I think it is in parallel with the main light? Or is it in series? Must be parallel because it is currently open.
You could measure voltage in that way, but not current. To read power you'd have to be drawing current from the generator, which will inherently reduce the voltage you read due to the resistance of the wire inside the dyno, and perhaps the magnetics. You'd have to set your DVM to read AC volts, which is no big deal, it will still be power. If you connected a resistor (12 ohms, at least 3 watts rating) to the dyno's outputs and did the measurement and recorded the data, you'd be able to compute power in very real terms. This would be a rigorous measurement of power.
If you can do this it would be nice to get speed at the same time, and graph power over speed. It should increase with speed, up to a point. Touch the dyno from time to time. If it gets uncomfortably warm, you're probably at a reasonable upper limit.
You could also do this with the bike stationary and the wheel driven by an electric drill with a rubber disk rubbing on the tire, with a cheap Cateye or something computer reading speed. The dyno only "knows" it's turning and producing current, not that it's on the road or not. You should be able to verify the German spec and discover how much power you can really get at your riding speed.