Originally Posted by
Trevtassie
Just so you know, pretty well everything you've said here is not well informed.
The efficiency of conversion for most dynamo to USB chargers is now in the mid to high 90s percentage wise. So even if you did want to extract 20W it's not going to take 30-35W watts at the crank.....
At this article:
https://www.cyclinguk.org/sites/defa...ub-dynamos.pdf
on the third page there are two graphs, one for drag and one for electrical output. When you compare drag and output you can see that there is a lot of inefficiency in the hubs.
But it is my understanding that the chargers that convert the AC current into USB 5v DC have the high efficiencies you cite.
My point is that if you wanted 20 watts of power, you might need 30 to 35 watts at the crank due to the hub inefficiencies.
That said, nobody is going to want to pedal that hard, I am content with the output from my SP hub. If someone feels a need for 20 watts, it is their choice if they desire that much electronic stuff, I don't want that much stuff.