Dumb question, inappropriate forum. Sorry
This not an inappropriate question, and this is not an inappropriate forum.
Dc generators were used on cars up to about 1970, because the rectifiers for a high-current ac current (generated by an alternator) were not sufficiently compact or reliable. So the old generators had a stator excitation field coil, and the dc current output was taken off the armature via a commutator. These dc generators were often unable to produce a sufficient voltage and current at idle speeds to charge the battery.
In the modern automotive alternators, the armature coil is excited with a dc current via slip rings, producing a rotating dc multipole magnetic field. The alternator output is taken off the stator as a high frequency ac 3-phase current. Rectified 3-phase voltage has significantly less voltage ripple than recifiied single-phase voltage. Three pairs of rectifier solid-state diodes, usually inside the alternator case, convert the ac to dc. Because of the ac frequencies, the magnetic components (especially stator) have to be laminated.
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