Load Dump — Electrical
A high voltage pulse lasting hundreds of milliseconds that appears on the supply line when the battery connection is broken while the alternator is working under load. In unsuppressed systems it can reach tens of volts on a 12 V line; because of its duration and energy it is far more destructive than an ordinary voltage spike.
The mechanism of the event is this: the alternator field is set to deliver a certain current when the load is suddenly lost. Because it takes time for the regulator to reduce the field, the energy produced holds the line at high voltage for typically 100-400 ms. Removing the battery with the engine running, a loose battery terminal and a broken supply cable are the classic causes of this event.
This pulse is different from short spikes: because its duration is long, the energy it carries is on the order of joules and small suppression devices cannot absorb it on their own. Modern vehicle alternators have suppression inside the regulator, but in agricultural and construction machinery applications this protection is not always reliable.
The practical measures are these: keep the battery terminal clamps tight, never disconnect the battery while the engine is running, take the driver supply directly from the battery terminal and fit a suppression device of a suitable class at the input. A significant portion of the failures where electronic modules burn out "for no reason" are supply-related events of this kind.
The context in which this term is used: DC Motor Driver Selection Guide
Do not confuse: what is described here is the electrical voltage pulse originating from the alternator. For the speed runaway caused by the load being removed from the motor, see the entry Load Rejection — Mechanical.