Load dump
Encyclopedia
Load dump means the disconnection of a powered load. It can cause 2 problems:
In automotive electronics
, it refers to the disconnection of the vehicle battery from the alternator
while the battery is being charged. Due to such a disconnection of the battery, other loads connected to the alternator see a surge in power line. The peak voltage of this surge may be as high as 120 V and the surge may take up to 400 ms to decay.
. When the vehicle battery is being charged, the alternator supplies it with a large current. If the battery gets disconnected while it is being charged, the alternator current drops sharply and suddenly. This causes a high voltage across the alternator due to the inductance of the field winding. The field current cannot drop quickly, so the magnetic field remains large, so the rotation of the alternator continues to generate a large voltage.
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. This kind of a spike would damage any semiconductor device, e.g. ECUs
, that may be connected to the alternator. Special protection devices, such as TVS diodes
, varistors which can withstand and ground
these spikes may be added to protect such semiconductor devices.
Different automotive standards such as ISO 7637-2 and SAE J1113-11 specify the standard shape of the load dump pulse against which automotive electronic components may be designed.
There can also be an inductive spike due to the inductance of the field winding. That may have a larger voltage, but it will be for a much shorter duration, as little energy can be stored in the inductance of a field winding. Load dump can be more damaging because the alternator continues to generate power from the rotation of the engine, so much more energy can be released.
The inductance of the current-carrying windings has no direct effect on the load dump, but it has a large indirect effect. In normal running, current flowing in the inductance of the windings causes a large voltage drop. To keep the correct terminal voltage, the magnetic field from the field winding has to increase a lot at large loads. When the load is disconnected, there is no current, so there is no voltage drop in the inductance of the windings. The full voltage appears on the alternator terminal until the field current falls.
- failure of supply to equipment or customers
- large voltage spikes from the inductive generator(s)
In automotive electronics
Automotive electronics
Automotive electronics are the electronics used in the automobiles.It includes body electronics, in car entertainment, carputers, chassis electronics and telematics.Automotive electronics...
, it refers to the disconnection of the vehicle battery from the alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
while the battery is being charged. Due to such a disconnection of the battery, other loads connected to the alternator see a surge in power line. The peak voltage of this surge may be as high as 120 V and the surge may take up to 400 ms to decay.
Overview
The windings of an alternator have a large inductanceInductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
. When the vehicle battery is being charged, the alternator supplies it with a large current. If the battery gets disconnected while it is being charged, the alternator current drops sharply and suddenly. This causes a high voltage across the alternator due to the inductance of the field winding. The field current cannot drop quickly, so the magnetic field remains large, so the rotation of the alternator continues to generate a large voltage.
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. This kind of a spike would damage any semiconductor device, e.g. ECUs
Electronic control unit
In automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....
, that may be connected to the alternator. Special protection devices, such as TVS diodes
Transient voltage suppression diode
A transient-voltage-suppression diode is an electronic component used to protect sensitive electronics from voltage spikes induced on connected wires....
, varistors which can withstand and ground
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
these spikes may be added to protect such semiconductor devices.
Different automotive standards such as ISO 7637-2 and SAE J1113-11 specify the standard shape of the load dump pulse against which automotive electronic components may be designed.
There can also be an inductive spike due to the inductance of the field winding. That may have a larger voltage, but it will be for a much shorter duration, as little energy can be stored in the inductance of a field winding. Load dump can be more damaging because the alternator continues to generate power from the rotation of the engine, so much more energy can be released.
The inductance of the current-carrying windings has no direct effect on the load dump, but it has a large indirect effect. In normal running, current flowing in the inductance of the windings causes a large voltage drop. To keep the correct terminal voltage, the magnetic field from the field winding has to increase a lot at large loads. When the load is disconnected, there is no current, so there is no voltage drop in the inductance of the windings. The full voltage appears on the alternator terminal until the field current falls.