Opening the hood on a typical electric vehicle can be a frightening experience for some people. We have all heard that these vehicles carry high voltage often in the 200–800-volt range!
The owner’s manual informs us that all the high voltage circuits will have some sort of orange identification but what does that mean? It simply means that if a circuit harness carries high voltage, it must be at least wrapped to some degree in orange tape (not necessarily the entire harness). If a component is considered high voltage, it must have a warning sticker on it clearly visible for anyone servicing these vehicles. You can clearly see that the sample photo of the chevy bolt abides by these rules.
Car manufactures have built many safety mechanisms into the electric vehicle’s operation for both the consumer and the service technician. First, we should start by saying one should always refer to the safe practice procedures set forth by the manufacture before attempting any service on these vehicles. One should also seek out quality training on how to test for any high voltage threats before removing their PPE devices.
All hybrid, plug in hybrid and full electric vehicles will still have a conventional low voltage 12-volt system to operate many of the vehicle’s electronics such as computers, headlights, wipers etc. The 12-volt system is also needed to power up the high voltage circuits. Without a properly functioning 12-volt system, the high voltage is as good as dead in all areas except the internal HV battery pack. Let’s talk about two common safety devices that the manufacturers use to assure the safety of all involved.
Interlocks are commonly found on high voltage components. Components such as inverters, on board charging modules, d/c to d/c converters, junction boxes and even some battery compartments. The job of the interlock is to open the HV circuitry when a cover is removed. These interlocks can be bypassed by trained service personal when live circuit testing is required but a do it yourselfer without having been properly trained by the manufacturer should never attempt to remove any covers on an electric dive type of vehicle! The following photo shows an interlock from a Toyota Prius’ inverter assembly. This type of interlock is essentially just a shorting bar that once the cover has been removed will be taken out of its connector along with the top cover. In theory, once the circuit is opened, the HV threat located inside the inverter should be eliminated. Again, before taking any manufactures word for it, always perform a SAFE measured reading before removing your high voltage protective wear.
Another interlock is tied into the SRS or air bag system. Manufacturers have implemented the use of pyro fuses and traditional crash sensors that will also prevent the HV from leaving the battery pack assembly in the event of air bag deployment.
Another safety device that all manufacturers are using are HV switching contactors. Often, a vehicle will have at least two HV switching contactors. One for the HV positive cable and another for its negative cable. Think of these as fancy relays for high voltage circuits. When the driver presses the start button on the dash, a 12-volt ignition signal is sent to the low voltage side of the switching contactors through the pre-charge relay and system’s main resistor. This low voltage signal will close the contactors thus allowing the high voltage from the battery pack to power up the rest of the high voltage circuits. Without the contactors closing, the HV threat in theory, remains inside the battery pack. Again, one should always prove out the absence of any high voltage before removing any PPE devices.
These are just a few examples of how the manufactures have tried to incorporate various levels of safety into electric drive vehicles. These vehicles should not intimidate anyone when purchasing a new vehicle. An internal combustion engine has far more dangers than their counterpart, the electric drive vehicles.