On Thu, 11 Aug 2016 09:20:09 +0100, charles wrote:

In article , 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 remember seeing some dynamo systems which had a battery container
attached to the frame. The advantage of batteries was that when you
stopped moving - eg at traffic lights, your cycle lights stayed on. But
nowadays cyclists never seem to stop for traffic lights, so behaps a
back-up battery isn't needed. ;=)

I had one on my bike in the early to mid sixties (which also had a hub
dynamo). Alloy tube which held about three U2 batteries (whatever they are
called now). The headlight had a 3 position switch underneath; on, off,
battery.

Cheers


Dave R



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