SAE J2990-2:2020 pdf free

SAE J2990-2:2020 pdf free.Hybrid and Electric Vehicle Safety Systems Information Report
Consider the situation of Figure 1. Such an accidental connection between a power system conductor and the earth (ground) is called a ground fault, modern vehicles have fault protection programed into the operating system with Diagnostic Trouble Codes (DTC) to provide information. Ground faults may be caused by many things, including dirt buildup on high voltage insulators (creating a dirty-water path for current from the conductor to the technician, and to the ground), ground water infiltration in buried power line conductors, and birds landing on power lines, bridging the line to the pole with their wings. Given the many causes of ground faults, they tend to be unpredictable. In the case of trees, no one can guarantee which wire their branches might touch. If a tree were to brush up against the top wire in the circuit, it would make the top wire safe to touch and the bottom one dangerous – just the opposite of the previous scenario where the tree contacts the bottom wire (see Figure 2)
With the tree branch theory in mind, the vehicle is similar to this scenario. One-hand work on high voltage is a must for technicians working on or around possible high voltage equipment. In most cases the high voltage has been isolated to a split power pack, meaning there is no path for the current to flow unless it is shorted. Since in a collision the technician does not know what wires are touching it is not always safe to assume the fault system has been activated. Caution and not becoming the ground path is essential.
Conventional vehicles generally use low voltage electrical systems, commonly a 12 volt system, to run lights, horn, power door locks and various other vehicle loads. A 12 volt electrical storage battery is used to supply energy to these devices even when the vehicle’s engine is not running. Some smaller hybrid systems might use this low voltage battery as power for a hybrid motor, but many classes of hybrids require larger batteries with higher voltages to provide the necessary power. Hence, xEVs often have two nearly independent electrical systems.SAE J2990-2 pdf free download.