Originally Posted by
steelbikeguy
can you elaborate on the shortcomings of hub dynamos regarding rpm?
The German standard requires the dynamo to bring the light up to full power at a fairly low speed.... 10kph or so, IIRC.
Steve in Peoria
I'm thinking about charging a battery or USB device, not lighting. In this case, the wide range of wheel rpm means you won't get full charging capacity (eg, USB requires 5W) until you are moving fairly quickly.
Originally Posted by
HerrKaLeun
Unless you are climbing steep hills, the hub runs at higher rpm than the crank. And on steep hills you likely are OK giving fewer Watts to the dynamo. So a crank dynamo would have to be physically larger for a given power output.
If you took power from the chainring, you could gear back up to something more reasonable.