Why would an electric car need a separate 12v battery like an ICE powered vehicle?

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In reference to [this post. ](https://www.theverge.com/2024/6/21/24183439/tesla-model-y-arizona-toddler-trapped-rescued)

In: Engineering

6 Answers

Anonymous 0 Comments

I have Toyota hybrids, they also have a 12V battery. 

There’s a safety/reliability play also. Have a separate power supply should separate bus voltages – no way that parts designed for 12V can see the battery voltage (277V (I think) in Toyota hybrids). Means the start button can’t somehow see more than 12V. 

12V runs the “always on” items to keep drain off the HV battery. Car always has some power draw for unlock/start commands. Teslas must have an inverter/transformer to charge the 12V system from the main battery back (equivalent to an alternator in ICE vehicles). 

Anonymous 0 Comments

Nearly every part made for modern cars that works off electricity uses 12V; radios, motors, sensors, etc. It is easier and cheaper to use those existing parts. It is also easier, cheaper, and more efficient to run those parts from a 12V battery than to convert the high voltage of a larger battery down to 12V all of the time.

You could go to the store (high voltage battery) for every meal but it is easier and faster to grab something from the cupboard/pantry (12V battery).

Anonymous 0 Comments

The high voltage battery and the 12V converter do not run all time when the car uses turned off. In most EVs those components only run when the car is on, when it is charging and for a short time once a day or whenever it senses the 12V battery is getting low to charge the 12V battery back up. Running them all the time would require running the high voltage battery heater/cooler all the time and would waste a lot of power.

Anonymous 0 Comments

In addition to the other comment, it enables a system where the high voltage battery is disconnected when the car is turned off, for safety.

The 12V battery engages a relay which connects the high voltage supply to the motors and controls.

Anonymous 0 Comments

Everyone talking about it being cheaper to run radios and stuff but Im pretty sure DOT requires cars to have emergency flashers that run even if all other systems have failed.

Anonymous 0 Comments

Either you add a transformer to bring the electricity characteristics from the big battery to compatible with the electronics. Or you put a battery that will be directly compatible. Given batteries in this segment are mature, and transformers not so much, the 12V battery must be used.