Battery disconnecting is an operation that occurs, or at least should occur, on nearly every car that is repaired. Welding discharges substantial energy in order to generate heat to melt metal. It’s easy to understand the amount of heat required to melt metal, now realize that during welding the metal is reaching that temperature instantly. For this instant melting of metal, a focused and intense amount of energy is needed. Car computer systems operate on 12-volt DC current, with some sensors using a 5v reference. Welders operate on no less than 110-volt AC current and when grounded to the vehicle body, represent a real risk to every ECU on the vehicle. Even a stud gun or a dent puller sends energy into the metal to weld the tip of the machine to the panel. Those, too, are 110-volt current, and again, they, too, take an intense energy
|(Photo courtesy of Pete Meier) Working on a hybrid? Don't attempt to disconnect the HV battery or any of its related components without proper training and safety equipment."|
When the vehicle's battery is connected, a path to all of its electrical systems potentially exists. The energy from the welders can therefore over energize and thus damage the electrical components. Any time a welder or dent puller is used a battery should be disconnected. There is one more area that always requires the battery to be disconnected prior to repair, and that is when working on SRS components. In addition to disconnecting the battery, most OEMs specify a period of time that you must wait prior to disconnecting any of these system components to avoid accidental deployment.
Vehicles are now often equipped with two batteries, a primary battery and an auxiliary battery. With the large array of computer systems vehicles today are having to share responsibilities across multiple batteries. The primary battery takes care of the standard vehicle operations, the starter, engine control, and other basic features. The auxiliary battery will handle things like navigation, advanced air conditioning systems, lighting and other high power using accessories. It is critical to know if the vehicle being worked on has just one battery or multiple batteries. Disconnecting only the primary battery will not suffice in proper electronic protection during welding, SRS repair, or other repairs that require the primary battery to be disconnected. The auxiliary battery may not be located near the primary battery or even with-in eye site. It is critical to pull repair procedures to discover if a vehicle has additional batteries and if so where they are.
The high voltage batteries used in hybrids is a story all by itself. These vehicles also have an auxiliary 12v battery in addition to the HV battery. Don't attempt to disconnect any HV battery or HV system component without proper training and safety equipment.