The best overvoltage protection device on a truck electrical system is the battery banks that help condition system voltage and smooth out high-voltage spikes. Emergency operation without the batteries or with deficiencies on the insulated side of the battery circuit can produce extreme voltage transients (short duration spikes) that can damage both solid-state and electrical components. Some electrical circuits are susceptible to load dump, a condition that occurs when current flow to a major electrical consumer is opened, creating a voltage spike.
Zener diodes can be installed in the rectifier bridge to limit high-energy voltage spikes. These can be used elsewhere in the electrical system to protect voltagesensitive components. Other solid-state overvoltage protection devices can be used to protect the alternator ground circuit for voltage spikes. These are designed to short the alternator to ground at the excitation winding.
CAUTION: Truck alternators are not provided with reverse-polarity protection. Reverse-polarity connections such as those caused by jump-starting can destroy alternator diodes and numerous other chassis solid state devices.