I too am building a “full electrical system” for my MB. However, I’m not planning to power it from the engine, which puts out 6v +/- at 3 Watts +/-. This is what I’ve learned so far:
For a 12v system, you should plan to use 12v LED tail, stop, and turn signal lights because these use the least power. For the headlight, in my opinion you will need a 20 Watt (minimum) up to a 50 Watt incandescent bulb with a good reflector to create enough light to safely go 25 MPH+ at night. Incandescent bulbs of lower power don’t put out enough light.
I built a headlight using a 4" dia. PVC cap, some aluminum bar stock, and a 20 Watt landscape flood light. See the attached photos.
Unless you get creative (see ZnsaneRyder post above), LED headlights seem to produce a relatively dim flood pattern or a bright and small spot pattern, but not both at the same time. In my opinion, they don’t put out the “volume” of light that is needed to drive safely at night. Not only do you need to see the road, but you have to be seen by other traffic as well. Consequently, having a thin beam that produces a bright spot in front of the bike isn’t necessarily good enough to keep you safe. You need a bright area in front (spot) and a relatively wide (flood) light pattern side to side as well. Look at your car’s headlight pattern – bright in the middle, with a dimmer, but wider flood pattern to the sides.
Generally, the more power a light draws (in Watts), the brighter it is, but the more load it puts on your batter/charging system. A 20 Watt bulb will draw about 1.7 amps of current and a 50 Watt bulb will draw about 4 amps (Power = Current x Voltage, or P=IxE. Therefore, I=P/E). A 7amp-hour 12v battery will last about 4 hours powering a 20 Watt bulb, and about 1.75 hours powering a 50 Watt bulb.
If using a 12v gel cell battery in your electrical system, the brightness of the headlight will diminish with time as the voltage decreases. You should not let a gel cell battery go below 10.7 volts or you shorten its life. The “best” battery to use may be one made from nickel metal hydride (NMH) cells. NMH batteries are light, have a flat discharge curve, but “die” quickly with little notice. NMH batteries don’t have a memory effect like nickel cadmium batteries. Another nice thing about using other than gel cell batteries is you can buy or make a battery that puts out more or less than 12v. You can drive a 12v bulb with 14.4v to get a brighter light with shorter bulb life, or with will less then 10.8v to get less light, but longer bulb life.
Wheel-driven, and hub bicycle generators provide 3 to 6 Watts of power, which is probably enough to power the LED tail, stop, and turn signal lights, but is way too short on power for the headlight. I doubt the generator/alternator in your small motor puts out more than 6 Watts. You will likely need a battery in your electrical system to provide power for when you turn on the headlight.
FYI, Harbor Freight Tools is selling a package of two, rectangular, 12v, 50 Watt spot lights for $7 until June 6, 2009. Normally they sell for $14. The lights have a relatively clear lens, and a relatively light black plastic housings with a mounting bolt. Good for experimenting.
