And would it matter, as we aren’t using the 12V to “start” our cars, more to power accessories.
Actually, Tesla made a design decision with the 3 that means we are using 12V to start our cars. Let me explain. Inside the battery pack is the High Voltage Controller (HVC). It is actually directly connected to the battery pack. It supplies 25V power to the High Voltage Processor (HVP) and High Voltage Battery Management System (HVBMS), and 10V power to the pyro disconnect. Those systems are what report battery capacity to the main computer, and control opening/closing the High Voltage Contactor.
The Power Conversion System (PCS) produces 12V to recharge the battery, but the PCS only works when the HV Contactor is closed.
Because the HVC is directly connected to the battery,
it will continue to function without 12V power, but cannot begin operation without 12V power. So without 12V power, the car can't close the contactor to allow the PCS to make more 12V power.
I'm hoping that in the future Telsa upgrades the HVC so there is a backup way it can start operations without 12V power OR the car could be upgrade via software to enter an "OH SHOOT" mode when the 12V battery dies where the car stays on and PCS maintains a 12V output indefinitely - it would use up range, but the car would remain drivable.
Would you rather the car just refuses to work when the 12V battery dies? Or you get a message that say "12V battery dead. Increased main battery usage to compensate will result in higher standby losses. Please replace 12V battery ASAP. If main battery reaches 20% power support mode will be disabled and car will be unable to start"
PS: Yes, this means you can jump a Tesla from another car. I would do it differently than normal jumping though. Normally, when jumping an ICE, you keep the engine running in the donor car. I would turn the engine off when trying to jump a Tesla. Once the Tesla turns on, it should start trying to charge the bad 12V battery, and the Tesla should continue to run until turned off.
