Last month we discussed alternators to see what goes on inside them, and how they work. We saw that the rotor rotates an electromagnetic field inside a stationary winding called a slator. Diodes rectify the AC voltage induced in the slator, changing it into pulsating DC to charge the batter and run the vehicle’s electrical systems. That’s important to remember. The alternator’s job has two parts: it must not only charge the batter, but also operate the electrical/electronic system all at the same time.