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this post was submitted on 24 Jun 2024
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Really interesting design decision. Was the main battery also dead? I'm guessing not. There's a step-down converter under the rear seat that outputs 12-16 volts, Tesla could probably have fairly easily set the car up to power the doors from that when the auxiliary 12V battery dies.
Probably would still need the 12V battery to have enough charge to close the connection to the high voltage battery that would power the step down converter.
But yeah it seems dumb to me that most EVs don't keep the 12V battery topped up from the high voltage battery somehow while the car is parked, but I'm not an electrical engineer ¯\_(ツ)_/¯
There really shouldn't need to be a 12V battery at all. Stepping the voltage down isn't that complicated, but the supply chain for the necessary parts aren't there for the car industry.
Plus, it'd be really nice if everything could run off a 48V line instead of 12V. The wires can be thinner due to less current draw. Getting that to work across all the electronics for everything is a whole separate level, though.
You don't want to fully drain the main battery as it would do severe damage to it and most of the 12v system has a phantom draw of power so to keep the main battery from running out they have a separate one
Compared to what the main batt can provide, there's barely any draw from the other electronics.
That's not the point the fact is that there is some dumbass that probably will let it sit at 0% and kill the battery
Battery management electronics don't let you drain lithium batteries to 0%. It's a severe design flaw if it does.
I think it's mainly there just to be able to control the circuit that cuts power to the high voltage battery off while the car is parked for safety reasons.