Why not go back to a few fundamentals? When a wire is moved through a magnetic field, a current is generated in the wire. In physics the prof had a large permanent magnet shaped like a horseshoe. When he moved a plain wire between the two ends of the magnet, it made a big very sensitive meter needle move, and the faster he moved the wire, the further the needle moved proving he was making a weak electric current in the wire. If he made a bundle out of the wire and passed it between the North and South pole, the needle moved much more. So a generator is just a very long wire wound into an "armature". When this is made to spin very rapidly between two magnetic poles, you have a generator or dynamo. With different ways of winding the armature and placement of magnets, either direct current or alternating current can be produced. In the early days, Thomas Edison favored direct current, because it would drive a motor with more power, such as those used in elevators. But the direct current generated at Niagara Falls had its voltage drop so fast in the transmission lines that it could not be sent to New York City. Along came a Hungarian, Nikola Tesla, who showed that alternating current was more desirable because its voltage could be raised or lowered by transformers, and so it could be transmitted for great distances. So alternating current became the widely used system of today. When semi-conductors became available, it became possible to raise voltages of direct current, and now direct current can be transmitted long distances with very low losses, and then turned back into alternating current to use in the home. The early automobiles used direct current generators to charge the battery. But when motor was idling, current output was insufficient to keep battery charged. When semiconductors became available, alternators in cars could keep battery charged even when idling. So cars now all have alternators. Dynamo and generator mean essentially the same thing, a means of turning rotatory motion into electricity. Alternator just specifies that it produces alternating current.
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