Originally Posted by
Tourist in MSN
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.
I think that’s the takeaway from all of this - you either have to be pretty careful with your power needs or ride a long/appropriate time or find another power source. From those charts, it’s probably prudent to plan on something less than the 5W peak output and factor that against the time you can ride per day. If your needs are below that, you’re good.