As there has been a bit of debate about regulators and alternators in this thread I thought I'd add my two cents worth having been in the electronics industry since 1980.
Alternators produce AC (Alternating Current)
Wiki on Alternators:
http://en.wikipedia.org/wiki/AlternatorFrom Wiki:
"Automotive alternators invariably use a rotor winding,[citation needed] which allows control of the alternator's generated voltage by varying the current in the rotor field winding." This is how they achieve regulation of the output voltage. As the current draw increases, the voltage tries to drop. (Power = Current x Voltage) so teh exciter coil is energised harder to make a stronger "magnet" which produces more voltage. As the current draw drops the exciter coil is driven less hard bring teh voltage back to the correct level.
Alternators are more energy efficient with most of them being 3 phase alternators, meaning that there are three sets of coils producing energy, but the coils are 120 degrees out of phase with each other. (360 degrees per circle/cycle). by having them out of phase it requires less energy to pass each coil through the magnetic field and because they rapidly follow each other there is a constant supply of energy. Each phase normally rectified in the alternator and the regulator is usually built into the alternator as well.
Automotive Generators usually produce DC (direct Current)
Most automotive generators are actually Dynamos:
http://en.wikipedia.org/wiki/Electric_generator#DynamoIt was the old dynamos that used either shunt or series regulators and sometimes both. The old Land Rover Series II had a Generator mounted on the engine and the regulator up on the firewall. It limited the voltage to 13.8V but could not stop it dropping low and it also regulated the current by limiting the current draw.
Hoping this clears it up.
