OT: Bicycle Lighting System?

 Posted here bco the obvious expertise of group members in matters
electrical.

Bicycle-mounted front wheel generator (alternator?) hub - puts
out AC.

Numbers on the hub say 6 volts, 4 watts.

Putting a volt meter on it, I get 3v at walking speed (2.5 mph),
6v at 5 mph, and more as speed increases.   With me on it, I
don't see it ever getting up to 20v, but 10-12v could be fairly
common.

From what I've heard, there is a problem with using bulbs wired
direct.   You get a bulb that won't burn out at the higher
voltages, and it's dim where most of the riding happens - at 5-10
mph.  It also goes out when the bike goes really slow or stops.

I'm basically clueless re/electrical stuff, but what I've gleaned
so far is this:
------------------------------------------------------------------
1) Something called a bridge rectifier will convert AC to DC.

2) If I put a couple of 1.5v NiCad batteries end-to-end, but    
   across the rectifier's output, they'll be charged when the
   output exceeds 3 volts and supply 3 volts when the output is
   less than 3 volts - limiting the voltage that any bulb or
   LED emitter is subjected to about 3 volts.

3) There are myriad 3-volt LED lights out there that I can choose
   from for the lighting part.  Red, white, steady, flashing....
   you name it, somebody's selling it.
------------------------------------------------------------------

Bottom line, I want maximum brightness when just noodling along
at 3-7 mph, but don't want tb burning out bulbs if/when I go down
a hill fast.

My primary concern is the lighting that's visible to closing
traffic from my back.  I avoid roads with any significant amounts
of traffic, but even in the quietest neighborhoods and parking
lots there's some exposure.  

The more light and the more attention-getting on the rear the
better, since I'm competing with cell phones, text messages,
email, and navigation screens.

I use a hand-held flashlight for the front lighting and it works
well.  (Lowe's TaskForce 4w LED... one *brave* little flashlight)
.. but I also want a token front light attached to the bike and
wired into the system in case some cop wants to get technical or
the hand-held fails when I still have to get back to my home.

Am I on the right track?   Seems like the capacity of the
rectifier would be a half amp max (4w/20v + fudge factor).

One more time: I'm clueless about electrical stuff.
--
PeteCresswell

  I use one of those flashing LED rear lamps.

And a converted head lamp with a 6v Kryton bulb driven off 4 1200mAh AA's. Its
2hrs of light.

You could use this araingment and use your Hub generator and a Bridge tied to
the batteries. Not a problem for short trips or
a casual rider, but extended trips and high speeds may over charge the batteries.

Also, be sure your hub is isolated. Other wise if one end of the hub winding is
tied to GND then a single diode should be
used instead of the bridge.

4W at 6V is 0.666 A a 1A rectifier is best,


HUB---------|
            |
           /A\
          /   \
GND _____/-   +\___________________Lamp
         \     /    |
          \   /     |        GND---Lamp
           \A/      +B
            |        A
HUB---------|        T
                    -
                    |
                    GND
Cheers

 Per Martin Riddle:

That was *quick*... I'm not even seeing my OP yet.

Is the diagram above predicated on an "isolated" hub?
--
PeteCresswell

 

 Per Martin Riddle:

2hrs of light.

There's not doubt whatsoever in my mind that the rational
solution is battery-powered lights.   They're everywhere - and on
sale right now at Performance.  Witness my own hand-held
flashlight (2 C batteries - probably be putting out light on the
original batts long after I'm dead...)

But now I've got this Sturmey-Archer Dynohub (was planning on
just a drum brake... but the drum + generator was only five bucks
more...) so, just for grins, I'd like to make a system that works
without batteries.
--
PeteCresswell