I have questions: Does this seem right to you?
Using a 6V, 3W 0.5A Dynamo.
The voltage is clamped to a set level. (Zener Diode)
Clamp voltage is 3V you get 0.5A and 1.75 Watts. Half power at 4Km/h, Full power at 7Km/h.
Clamp voltage is 6V you get 0.5A and 3.5W, 7Km/h, 15
Clamp voltage is 9V you get 0.5A and 5.25W, 10Km/h, 20
Clamp voltage is 12V you get 0.5A and 6.9W, 12Km/h, 20
Clamp voltage is 15V you get 0.5A and 9W, 15Km/h, 25
Clamp voltage is 18V you get 0.5A and 11W, 18Km/h, 30
There is little to no increase in power at increased speed?