# Help understanding generators/alternators

1. Nov 7, 2009

### wall6ly

Dumb question, inappropriate forum. Sorry

Last edited: Nov 7, 2009
2. Nov 9, 2009

### Bob S

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.
Bob S

Last edited: Nov 9, 2009