65 Ammeter now shows overcharge when accelerated

IIRC, the car is running off the battery until ~ 1100 rpm when the alternator is producing enough electricity to get involved. Power from an alternator remains relatively flat over the rpm range. A generator on the other hand produces more power the faster the armature is turned.

It amuses me when I hear someone say they left their car running to heat or cool the interior and to charge the battery. The fan is set on high and the car is idling. The voltage may look fine, but an ammeter would be pegged. Who puts an ammeter in a car in this era anyway?