On 3/6/2017 2:12 AM, DATAKOLL MARINE RESEARCH wrote:
Assumptions or measured ?

I forgot to respond to that question.

I've measured dynamo torque vs. speed. As James says, the resistance
torque of a dyno decreases as speed increases. It doesn't decrease as
much as speed increases, however, so the power required still increases
with speed.

Example: Soubitez roller dynamo

Speed (mph) 6 12 18 24
Torque (N*mm) 26.4 22.6 18.1 14.3 with 12 Ohm load
Torque (N*mm) 22.6 23.4 19.6 15.1 with 24 Ohm load

I found similar behavior with other dynamos.

With an open circuit, drive torque did increase with road speed.

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- Frank Krygowski