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What Causes an Alternator to Overcharge?


The alternator in an automobile functions as a self-generating power plant that produces electricity. It converts alternating current (AC) to direct current (DC). It must supply enough electrical energy to the battery for recharging, along with maintaining sufficient voltage to run the vehicle’s accessories and components. Original factory alternators come fine-tuned from the factory to meet the precise needs of the vehicle’s electrical demands, including charging level and intensity. A few problems can result when an alternator undercharges or overcharges the electrical system.


Alternators that overcharge will typically produce excess voltage to the battery, making the battery case swell up, become very hot and lose its electrolyte through boiling. Improperly jump-starting the vehicle can send a surge through the battery that destroys one or more cells in the battery or shorts it out. This surge disrupts the wiring in the alternator, causing an overcharging condition. Additionally, an incorrect replacement battery in the vehicle can cause an overcharging condition. This happens in newer vehicles with alternators that need signals from the vehicle’s electronic control unit.