On 9/24/2014 10:17 AM, Ian Field wrote:


"Andre Jute" wrote in message
...
On Friday, August 29, 2014 3:34:46 PM UTC+1, jbeattie wrote:
On Thursday, August 28, 2014 11:42:20 PM UTC-7, Lou Holtman wrote:
I don't know if a hub dynamo is a good thing on a mountain bike and
defer to those who use them. Personally, I wouldn't bother with one
because of all the wiring and additional crap on my bike that would
get infrequent use, being that night trail riding is not something I
would do often. A battery light would be a more reasonable option,
and I could simply shift a light from my road bike for trail riding.
I also wonder whether a dynamo would put out enough light when I was
picking my way up forested single track at 4mph. It seems to add so
much complexity without a real pay-off. The calculus is different on
a commuter that gets a lot of night time use.



-- Jay Beattie.

Either of the common topclass dynamos, Shimano sports version or a SON
appropriate to wheel size, will put out enough light. I have both and
the cheaper Shimano is excellent. The question is the
lightdistribution of the lamps they normally drive. The German lamps,
which are in many ways the best, are crippled by their legislation
and useless except on smooth well-demarcated roads. (Krygowski, with
his usual railroad vision, claims German lamps are socialized by being
limited to being like dipped car lamps, which is true, but it makes
them worthless for many common functions a cyclist demands of his
lamps; their socialization is one way, in favour of motorists.)

You don't have to be stuck with German light fittings, there's probably
oodles of other stuff on Ebay that will work with a hub.

There are "off-road" German lights that don't comply with StVZO and that
are usable. Unfortunately they don't include a flash mode. Daytime front
flashing lights are extremely popular because they greatly increase the
conspicuousness of bicycles during daylight hours. The only dynamo light
I've seen with the flash mode is the Planet Bike dynamo light.

It's really too bad that otherwise excellent lights are de-featured to
comply with StVZO and that there are so few full-featured models. But
since the market for dynamo lights in countries like the U.S. is so
small that's unlikely to change.

As I'm into constructing my own lighting sets, I'd probably start with a
rechargeable battery to charge off the hub, then rig something to run
off that.

Good idea. I have designed something similar. What you have to
constantly be aware of are conversion losses. The design I have runs the
light directly off the AC dynamo when the bicycle is in motion and only
switches to the rechargeable battery when stopped. There is no need to
always run the light on DC.

Also, use Schottky diodes for rectification as the forward voltage drop
is smaller.