On 11/08/2016 09:12, NY wrote:
"harry" wrote in message
...
Bicycle generators are all AC.
Why would they need to be DC?
Have you never dismantled one?

I'd never thought about this. For lighting it doesn't matter at all
whether you generate AC or DC - it's only when you need to power
electronic equipment (eg USB charger) that you need some form of
rectification and smoothing.

Do modern dynamos that can power USB devices still generate AC, or do
they have the commutator rings wired to reverse the phase of the
negative cycles to give full-wave rectification? I suppose it's about as
easy to modify the generator as it is to add a couple of extra diodes as
part of all the other electronics needed to provide a smoothed and
regulated 5V for USB, together with a bit of storage in a battery to
cover times when you are going slower or when you stop at lights.

I would put moving magnets inside fixed coils and have no commutators.