Originally Posted by Road Fan

Plano, you are assuming that the rating of the dyno is a power limiting value. I think it's instead a guaranteed level of performance at a specific road speed - the statement of compliance with the specifications of the German road law (I can't give the citation). At a higher road speed or at a lower electrical load impedance it may put out more than that. We don't know it's maximum power, short-term or long term because of several other uncertainties: we don't know if the standard (i.e. LED light) load is a matched load for any given generator, we don't know if the generator physical design is thermally limited (affects long term power output), and we don't know at what combinations of load and speed the magnetics saturate (electrical limit of the generator circuit).

I'd say (and I cannot say I can do this at my house, I could have done it three jobs ago when I was still a power electronics engineer) test the generator by spinning the wheel at fixed speeds and loading it with known resistor loads. Observe the load waveform with a current probe (or a shunt) and an oscilloscope. Take data to indicate at what power level the current is becoming distorted, also what the RMS voltages and currents are. Since it's an AC machine, power factor must be considered in assessing output power. Just for a little more fun and understanding, probe the dyno case temperature with a thermocouple right after each test to observe temperature rise with increasing power level.

While we're at it we should measure the Thevenin voltage and source impedance as well as the Norton current of the dyno.

With all this we'd have a good understanding of what the dyno's capability is.

I suspect you're exactly correct, that Mr. Bubbles' neat setup is not doing what he thinks it is, because he does not understand how the load circuit affects the generator. But now we should find the truth.