semantics question, generator or alternator Options

[type47]

So, I went to local FLAPS to have my "alternator" tested (it tested good) and they asked me if it was a generator (since it was so old) or an alternator. I said alternator. I looked it up in the PET because the guy testing it needed the part number (022.903.023 is -4) and the PET says it's a generator. What shall I call it and would that have any influence on the testing. Someone might explain the difference btw alt and gen. (gen doesn't need external current for the field windings, if I recall...)

[ClayPerrine]

Generator VS Alternator.

First some background. To generate electricity, you have to move a coil of wire past a magnetic field. The motion induces electrical current in the windings as it passes through the magnetic field. The spinning will cause the current to fluctuate as it spins due to the polarity of the magnetic field.

In a Generator, the magnetic field is created with permanent magnets. The armature is wound with wire, and a commutator assembly ( the split rings and brushes) are used to make DC voltage.


In an Alternator, the magnetic field is created by a coil that surrounds the armature. Battery voltage is used to energize the field, and the armature is turning, so it makes more voltage out than is required to energize it. The commutator is not a split ring, and the output is AC voltage. A series of diodes setup as a rectifier is used to convert the AC voltage to DC voltage that the battery can use.


Drawbacks to a generator are that the output voltage can vary. The advantages is that they don't need a battery, so you can push start a generator equipped car even if the battery is stone dead.