What is the difference between a dynamo and alternator?

A dynamo normally refers to a DC (Direct Current) generator. An alternator produces AC (Alternating Current) electricity. An alternator in a car actually generates 3 phase alternating current which is converted to direct current using a rectifier.

Generally, vehicle alternators are lighter, cheaper to produce, have better capacity over a wider range of speeds, take less maintenance and generally last longer than an equivalent generator. The one disadvantage is that they must have a battery in the circuit to excite the field coils.