In electronics, load dump means the disconnection of a powered load. It can cause 2 problems: * failure of supply to equipment or customers * large voltage spikes from the inductive generator(s) In

automotive electronics Automotive electronics are electronic systems used in vehicles, including engine management, ignition, radio, carputers, telematics, in-car entertainment systems, and others. Ignition, engine and transmission electronics are also found in truc ...

, it refers to the disconnection of the vehicle battery from the

alternator An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.G ...

while the battery is being charged. Due to such a disconnection of the battery, other loads connected to the alternator experience a surge in the voltage on the battery bus. This surge may be as high as 120 volts and the surge may take up to 400 ms to decay. It is typically clamped to 40 V in 12 V vehicles and about 60 V in 24 V systems.

Overview

The field winding of an alternator has a large

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of t ...

. When the vehicle battery is being charged, the alternator generates a large current, the magnitude of which is controlled by the current in the field winding. If the battery becomes disconnected while it is being charged the load on the alternator suddenly decreases. However, the vehicle's voltage regulator cannot quickly cause the field current to decrease sufficiently, so the alternator continues to generate a large current. This large current causes the voltage on the vehicle bus to increase significantly -- well above the normal and regulated level. All the loads connected to the alternator see this high voltage spike. The strength of the spike depends on many factors including the speed at which the alternator is rotating and the current which was being supplied to the battery before it was disconnected. These spike may peak at as high as 120 V and may take up to 400 ms to decay.{{cite web, url=http://www.ti.com/lit/an/snva681a/snva681a.pdf , title=Load Dump and Cranking Protection for Automotive Backlight LED Power Supply , publisher=Texas Instruments , date=March 2015 This kind of a spike would damage many semiconductor devices, e.g. ECUs, that may be connected to the alternator. Special protection devices, such as TVS diodes,

varistors A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non- ohmic current–voltage characteristic that is similar to tha ...

which can withstand and absorb the energy of these spikes may be added to protect such semiconductor devices. Various automotive standards such as ISO 7637-2 an
SAE J1113-11
specify a standard shape of the load dump pulse against which automotive electronic components may be designed. There can also be a smaller inductive spike due to the inductance of the stator windings. That may have a larger voltage, but it will be for a much shorter duration, as relatively little energy is stored in the inductance of these windings. Load dump can be more damaging because the alternator continues to generate power until the field current can decrease, so much more energy can be released.

References

Power electronics