An alternator is self-limiting on current output, controlled by the resistance of the stator windings, so no current regulator is necessary. The battery's state of charge will determine how much current output the alternator produces, not the advertised current capacity of the alternator, so it's just about impossible to damage the battery if the voltage regulator is functioning correctly. The only time an alternator will even approach its max output will be for a short time after a hard start, when the battery is low on charge temporarily. Another possibility is if you have a HUGE sound system amplifier or something really stupid like hydraulics, etc. Electric cooling fans will draw more current than normal, but the alternator will supply any external load first, and use whatever capacity is left over for battery charging.
For example, let's say you have a 500 watt sound system amplifier (36 amps at 100% efficiency, realistically around 50 amps) and a set of fans that draw 20 amps. Add in ignition (10 amps), high beam headlights at 15 amps, and a heater fan at 20 amps. That's a 115 amp load that needs to be dealt with before any current gets sent to the battery, assuming you're running the woofers wide open, and it's a cold, rainy night and you're driving wide open throttle uphill so the fans are working hard. A 100 amp alternator wouldn't quite keep up with the load and the battery would supply the extra current. Turn off or reduce any one of the loads, and you're good to go. I have described a "worst case" scenario here, so a 100 amp alternator would be adequate for any reasonable operating circumstances. If you dump the stupid sound system, or at least cut back on the power demand, a 70 amp alternator would be plenty. When fewer external loads are operating, the alternator will charge the battery and run the ignition system at a fraction of its full capacity, and there will be plenty of reserve current available for other demands.
Jerry
