[T77911S]

an alt is a 3 phase generator. it has 3 pairs of diodes. one diode on each pair allows the positive portion of the sine wave of that phase to go to the battery and electrrics, the other diode sends the negitive portion to ground. if you look at the output of a bridge rect. with an O scope, it would look like a ramped DC, or a saw tooth. IE, the voltage may start at 13 volts and ramp up to 15 volts, then drop down and do it again. if you add a capacitor to the output, it smooths out the ramps and make a flat DC voltage. yes i am at work and putting off doing work right now, its early. if you just had one pair of diodes, the ramps would be steeper, or there would be more of a swing, say, 11 to 15 volts. (i dont know the exact volts, just numbers to give you an idea of what it looks like). plus, the 3 phase is more efficient.