This article is from the Misc Bicycles FAQs, by various authors.
From: tomas@Apple.COM (Tom Taylor)
About a month ago I built two lighting systems (one for my bike, one
for my wife's bike). Both systems have been very successful so I
thought I'd describe them here.
The main component of the system is a 20 watt 12 volt halogen General
Electric bulb. The bulb is a sealed bulb/reflector for a track
lighting system and costs about $11 at Home Depot. I made a small
clamp that fits around the base of the bulb and sealed it in place
with silcone sealant. I soldered some "zip" cord to the two pins at
the base of the bulb. Next, I masked off the front glass of the lens
and painted the whole assembly with automotive heat-resistent engine
paint. The whole thing is held on the handlebars with a large nylon
I built the battery in a normal water bottle. The actual battery is
made up of ten 1.2v 2400mah nicad solder-tab "C" cells. I soldered
two cells together end-to-end in series until I had five "sticks" of
two cells each. Next, I soldered each of the sticks together with
about 5" of wire (it looks like a string of sausages at this point).
Then I put some packing "popcorn" in the bottle of the water bottle
and started feeding each of the sticks in the bottle. The battery
sticks fit radially around the inside of the bottle. I drilled a hole
in the side of the neck of the bottle and mounted a mini on/off
switch. I drilled a small hole in the cap and mounted an LED. The
LED (and resistor) are wired in parallel to the outboard side of the
switch. The LED glows when the switch is on. I put it there so I'd
know the switch to the battery was on when I plugged the battery into
the charger. I wired up the battery to the switch, LED, automotive
fuse, and ran the wires out the drinking hole. The wire from the
headlight and battery have quick release electrical connectors. I
packed the rest of the water bottle with more popcorn.
I also built a rear taillight out of Radio Shack super jumbo super
bright LED ($4.99). I wanted the Vistalight strobing effect so I
built a tiny circuit based on a 3909 LED flasher chip. The whole
thing fits inside an empty 35mm film canister that is velcroed to the
underside of my bicycle's seat. The LED protrudes from the cap of the
canister and is very bright.
I've also wired up our Burley trailer with taillights. There's another
electrical quick-release for powering the trailer from the battery.
The whole system may sound clunky, but it's not! When the battery
isn't mounted in the cage, the weight penalty is insignificant. The
wire, front headlight, and film canister only weigh a few ounces.
The bottom line... performance. Since my officemate has a NightSun
team issue, I have something to compare against. My 20w light is
slightly brighter than a NightSun with both of its lights on (they
cliam 27watts). My light lasts about one hour and forty-five minutes.
As I mentioned above, I'm using 2400mah cells. I would guess that
NightSun's team issue battery is built with 2000 or 2200mah cells. I
guessed this from measuring their charging current (which is less than
200ma). Since you normally charge nicads at 10% their rated value for
14-16 hours, I assume they're using 2000mah cells.
Oh, I forgot! Building an appropriate charger is probably the most
difficult part of the whole system. I built mine out of an 18v Radio
Shack transformer and some diodes and resistors I found in my junk
box. The charger delivers 240ma to the water bottle battery.
GE 12v 20w halogen sealed bulb $11 ten 1.2v 2400mah nicads @ $5.20 each $52 switch $1 transformer $10 monster LED $5 wire, charging LED, fuse, resistors, diodes, clamps, water bottle. Already had
Total about $80