Without the battery to absorb the stator’s current, the output voltage surges to the very high voltages seen during unclamped load dump, as shown in Figure 3 from the ISO 16750-2 specification. This corresponds to the unclamped alternator scenario in “Test A—without centralized load dump suppression.”
Alternators with Internal Voltage Clamps
Newer alternators use avalanche diodes that have well specified reverse breakdown voltages which limit the maximum voltage during load dump. Figure 4 shows current flow during a load dump fault in a clamped alternator that uses avalanche rated diodes in the six diode rectifier.