Load Dump on a Tractor
A high-energy voltage rise lasting on the order of a hundred milliseconds that occurs when the battery connection is suddenly broken while the alternator is charging the battery. Since the battery is the largest buffer in the system, when it drops out the energy produced by the alternator is dumped onto the vehicle line. It is the highest-energy transient event known in vehicle electronics.
The mechanism of the event is this: the alternator's field current cannot fall instantly, so generation continues for a while. With no battery there is no buffer left to absorb that energy, so the line voltage rises far above normal and then decays slowly. Short as it is, the energy it carries is enough to destroy semiconductors permanently.
- Typical triggers: a loose battery clamp, disconnecting the battery cable while the engine is running, a corroded terminal post.
- Protection: keeping the clamps tight and clean, not touching the battery connection while the engine is running, supplying critical devices directly and through a fuse.
- Outcome: the damage is usually not visible immediately; the device fails inexplicably some time later.
That is why old habits such as "testing the alternator by disconnecting the battery terminal while the engine is running" must not be practised on vehicles with electronic equipment. The same logic applies to welding and jump-starting: the supply to electronic units is disconnected before these operations.
Context in which this term is used: Converting a tractor hydraulic lever to electronic control