Alternator Sizing - Amp requirements

When adding up, try to find "running current". I suspect many spec's such as radiator fans are for starting current, which drops greatly after the motor is spinning. At a high level, if your battery stays charged over a week of driving, your alternator is doing its job. One way to know is to put it on a 10A smart charger every Saturday morning and see how long before the charger shows "full". Another approach is to copy a modern car with similar loads, since the designers surely put in the smallest alternator which suffices, as every penny counts.

With a bigger alternator, you likely need bigger than factory wires, and probably bypass the alternator route into the cabin (to dash ammeter) to return to the battery. Search "MAD Bypass". I put large diodes in the underhood shunt route so current still routes thru my ammeter until the diodes start conducting it direct to BATT+.