From: strongw@bionette.cgrb.orst.edu (Willard Strong)
Subject: Generator/battery light setup
Organization: Dept of Entomology, OSU, Corvallis, OR, OSU, Corvallis, OR.
Date: Wed, 7 Oct 1992 22:07:09 GMT

Thanks to all who have responded with such helpful hints to
my request for aid in designing a lighting system in which
the bike-mounted generator recharges a battery-powered light
system. Here is the system I finally built. It first converts 
the generator AC to DC, then limits the voltage to 7.0, then 
charges the battery. The lights run directly off the battery.



gen-----------+
            /   \
          /       \  (+)    ----------
        +     R      +---+----   | V | | V |------+----------+------+------+ 
        | \       /     |    ----- |----      |      |      ||         /    /
        |    \          | ===    |    R1<          |      S      S   </
gen-----------+         |     |<    |>        |  B      |      | 
        |                C     +----+          B      |      |
        |                |     |               |      |      |
	|		|     R2              |      H      T
	|		|     |               |      |      |
	+---------------+-----+------D--------+------+------+  ---+
	             (-)		

gen = bicycle generator, Sanyo BB mounted unit, 6V 3W. Voltage, 
	no load is something like this:
		Bike speed	Voltage (NL)
		    3mph	   3
		    6              6
		    10		   9
		    14		   12
		    18		   14
		    22		   16
		    26		   17
		    30		   18
	Voltage with full load (3W) stabilizes at 8V AC at about 20mph.
R= full-wave bridge rectifier, 35 volts, 1.5 A
C= 500 mF 35 V DC capacitor. This takes most of the peaks out
	of the now-DC current.
V= Voltage regulator, variable from 1.7 to 37 V, peak current 1 A.  I
	would have preferred a2 Zener diodes but Radio Shack didn't
	have any over 1 W rating.
R1= variable resistor up to 1 K-ohm, "micro-pot", 0.10 W. The ratio
	between this and R2 determines the output voltage; I set it at
	216 ohms
R2 = 47 ohm resistor, ratio R1:R2 was 4.6 to get 7V output
D= rectifier diode, 1 amp 50 V. I found that current flowed back
	from the battery when the generator was off (i.e. through 
	the voltage regulator); the diode prevents this.
B= battery, 6V gel-cell
S= switches
H= 3W halogen headlight
T= 0.5W taillight

This system works quite well! It's my first electronics project
*ever*, so a real learning adventure. Here are the vital statistics:

	Bike speed	Volts DC	Current (mA)
	   3mph		2.5		100
	   6mph		5.04.5		>200 (my multimeter max's at 200)
	   7mph		6.05.5
	   8mph		7.0
	   10mph	7.0
	   15		7.0
	   25		7.0
The voltages max's at 7.0 regardless of load. However, when the
battery is hooked in, it keeps the voltage to the battery's voltage
until the battery is completely charged, then goes up and
maintains at 7.0 V.

There is a noticable drop in top-end performance with this rig. It
does suck some power, so that the generator produces less current
at low speeds. However, most of my riding is at 15mph or greater,
which is a net positive compared to what the lights take. Also, the
lights don't glow as brightly when screaming down a hill, because
it never hits that 8V it used to. But they glow strongly at 
intersections and up long hills, which of course they never used to.

Next I will get a new bulb for my 6 W halogen light, and hook it
up with another switch, so that when I'm on dark country roads
I can still see. This will use more power than the generator
produces, but since about 3/4 of my riding is in the daylight, Ilight, I
can keep the generator on all the time and it will even out. I
have to admit I like the idea of self-sufficiency this provides,
my legs making the light I see by rather than buying it from a
power company. I also find that the Sanyo BB unit produces almost
unnoticeable drag, at least on my fender-wearing, pannier-toting,
handlebar bag-clad, mirror-sporting commuter bike (I don't think
I would put it on my racing Bianchi though ;-).ing bike.

_Ward_
			*Oh, to light up the world with one's legs!*