Thread: Alternators

Hello, i have some questions regarding alternators say the car alternator.
I know that it uses the rotary motion of the engine to spin a magnet (rotor) inside the coils of wire (stator). I gues the rotor is basically an eletromagnet and it needs some current to produce the inducting magneting field. Well where does that current come from? From the car battery? Does it take an amount of current and produces say twice as much?

This page explains it. It's supplied by the battery until the vehicle is running.

http://en.wikipedia.org/wiki/Alternator

also here is a rather crude but useful video

http://www.youtube.com/watch?v=0VzvhfI4UpA