Originally Posted by
noglider
The drag is not that bad. It's so little that you can't feel it. But the power output is low. It's 3W (at 6V) nominally, not 6W. They could make dynamos that put out more, but then the drag would be intolerable. So they're great for powering lights, but that's because lights do great with 2 or 3 watts. But it's not enough or cost-justified for charging except in a very few cases. And even if it's good for charging, you should still have at least one spare external battery.
I run dynamo lights, and they work great for me. I run them day or night, so there is no charging available from the system.
I’d agree with that.
They work well for lights only. Dynamos are at the limit of their capability for that since there isn’t much left over for charging They really don’t work all that well if you have even modest battery needs by today’s standards. There is no real room left to add more charging capability in the design of dynamos because it’s going to eat into your rolling resistance pretty significantly if charging were to go to, say, 20W which would be reasonable but that would likely require 30-35W at the cranks (which would be a problem). 20W would be pretty reasonable and would be enough to support a single 5V/1A plus a single 5V/2.4A USB ports.
I see dynamos as useful if you’re completely off grid and have no access to an outlet. I also see them as being overtaken by solar panels pretty quickly.