The reasons alternators overcharge include issues with the battery, drive belt, alternator output, external regulator and type of alternator, explains AA1Car.com. Issues with these specific components result in the alternator overcharging the vehicle’s battery and electrical system. When this occurs, the alternator does not operate properly and malfunctions as the source of self-generating electricity.
A malfunctioning external regulator does not disengage properly, which causes the alternator to overcharge, AA1Car.com explains. This is the part of the alternator that regulates the amount of electricity the vehicle needs to perform at varying speeds. Alternator output is another reason for overcharging. Re-manufactured and replacement alternators are larger in size and offer a higher output than stock alternators. This causes inefficiency in the pulley on the belt drive, which causes the alternator to rotate more. The additional rotations increase the charging supply.
AA1Car.com adds that alternators have different designs that can incorporate computer sensors. Computer-controlled alternators use sensors to distribute voltage. The sensor regulates the amount of electricity the alternator produces. A defective sensor causes the alternator to overcharge by sending an inaccurate signal.
Alternators can also overcharge due to incorrect replacement batteries. This generally occurs in newer model vehicles when the alternator requires a signal from the electronic control system and the replacement battery does not send the correct signal.