Originally Posted by
wschruba
Just remember, if your frame/fork is carbon, without a place to mount the bottle already, the mounts almost universally have some kind of grub screw that pushes in the frame to keep it from rotating. Obviously, you can't mount those on carbon.
the grub screw is actually to make sure the light is grounded to the frame. Bottle dynamos only have a positive terminal, you have to complete the circuit through the body of the dynamo, and generally through the frame. I wouldn't put one on a carbon frame, but I'm sure there is some way you could hook the negative wire up to the body of the dynamo.
Carbon is conductive, but I don't think it would make a good negative return circuit.
The currently available dynos from Europe are a lot better than cheap ones, I think I would spend the extra $20 and get a good one.