Alternator Crowbar Load-Dump Test (100A) 

This video shows a demonstration of a "home-brew" alternator protection crowbar. During the test, the batteries were disconnected while charging at 100A. The crowbar system instantaneously applies a dead short to all alternator phases whenever a voltage excursion in excess of ~19V is detected.
This prevents damage to alternator diodes and other sensitive electronics connected to the alternator output. Without a crowbar system, disconnecting the batteries while the alternator is generating causes a destructive voltage surge, sometimes in excess of a hundreds of volts.
In this demonstration, the batteries were disconnected remotely using a remote battery switch (RBS) manufactured by BlueSeaSystems.
For video of bench test, see • Alternator Crowbar Ben...
DISCLAIMER: NEVER DISCONNECT YOUR BATTERIES WHILE YOUR ALTERNATOR IS RUNNING, OR START YOUR ALTERNATOR WITH THE BATTERIES DISCONNECTED!