Torque Shop: Regular 12-volt battery in EV is separate from high-voltage ones powering drive motor
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Complement: The 12-volt battery (with the red connector cap) is on a separate network of an EV to power the operational equipment.
ST PHOTO: CHRISTOPHER TAN
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I understand that my electric vehicle (EV) has a regular 12-volt lead-acid battery. What does it do and what happens if this battery goes dead or if the alternator fails?
Just as it is in any other type of passenger vehicle, the light bulbs, wiper motors, power windows, central-locking, infotainment system, climate controls and electronic control units in an EV run on a 12-volt direct current system.
The traditional automotive 12-volt electrical network has been in production for decades and has proven to be safe and reliable, while the battery is widely available and easy to replace. Component manufacturers base all their designs of on-board operational equipment, driver-interface, monitoring and safety controls, and every powered accessory, on the 12-volt system.
In addition, the voltage is well below the threshold that can cause injury. Occupants are therefore never in danger of electrocution even when any of the standard 12-volt equipment suffers a major malfunction or short-circuit.
On cars with internal combustion engines, the lead-acid battery is charged by a belt-driven alternator when the engine is running. For EVs, the battery is kept at full charge by the high-voltage (HV) 400- or 800-volt system via a converter.
The 12-volt battery system is separate from the HV batteries that power the EV’s drive motor and the air-conditioning compressor. Although it is possible to step down the HV to also run the ancillary systems in place of a separate 12-volt battery, the current technology keeps the networks separate.
This is to ensure maximum safety and complete isolation of the HV when the vehicle is shut down, during servicing or maintenance and in the event of a road accident.
When an EV is switched on, it is the 12-volt system that energises the switch that transmits high electrical power to be transmitted to the motors. This is a crucial feature of all EVs.
So, when the control system signals the HV to be disconnected, it is the 12-volt switch gear that isolates the HV. This will immobilise the EV drive.
However, the car’s power steering, brakes, power windows and central locking will still operate as normal, thanks to the independent 12-volt battery and its low-voltage network.
If the 12-volt battery fails, it is possible to use an external battery or power-bank to energise the low voltage network so that lights, door and boot locks and electronic parking brakes can function.
