Modified on: Wed, May 19, 2021 at 3:30 PM
Electric vehicles require two interdependent batteries: a high-voltage main battery that powers the drivetrain, and an advanced 12-volt lead-acid battery that handles key offloads. The 12-volt battery stores the power for the 12-volt system that runs components like the lights, instrument panels, door locks and alarm system, radio, as well as the battery management system and telematics. The 12-volt battery draws power from the high voltage main battery when the vehicle is on through the DC/DC convertor. The DC/DC convertor steps down the voltage from the high voltage main battery (typically around 400V), to around 14V which is required to charge the 12V battery.
For safety reasons, the high voltage main battery is electrically isolated when the vehicle is shut down due to its high store of energy which is more than enough to deliver a fatal shock. The battery management system (powered by the 12V battery), controls the isolation of the high voltage main battery through relays that connect the high voltage main battery when the vehicle is on, and isolates the high voltage main battery by disconnecting relays when the vehicle is off. Because the 12V battery controls the battery management system, if the 12V battery is flat or dead, it will not be possible to start the vehicle regardless of the charge on the high voltage main battery. The good news is that an EV can be jump-started just like an ICE vehicle using jumper cables.
Below is an illustration of the systems that are powered by the 12 volt battery in an electric vehicle.
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