I thought most don’t let you do that these days? I certainly remember that my old 2005 truck would cut off the dome light and headlights if you left them on too long, and my 2024 truck definitely does that.
I’m a little bit surprised that they’ve got two separate battery systems for the traction battery and everything else. I had assumed that even if they did use 12v for the “normal” stuff, that they just stepped the main battery power down to 12v from wherever it is at for the electric motors, and just had the single battery. Having separate batteries seems dramatically more complicated.
Although it is possible, it is more difficult because batteries are DC. With modern electronics, it is possible to convert DC to AC. You then use a transformer to change the voltage. Then, you change it back to DC.
I guess the problem is, with that system, the main battery is always “on”, even when parked and unattended, as the security (monitor cameras) the receiver for the key system, door locks, trunk and frunk and charge port, etc. are always on. It seems simpler to have the 12V battery as a smaller “reservoir” of the electricty needed for basic non-driving functions.
The other issue is that charging in most cars requires a communication between the car’s computer and the charger, for various functions - start, stop, identify car and set charge current, etc. (Tesla superchargers interrogate the car for its ID that determines who to bill for the charge). With the 12V battery, the main battery can be drained and you still get the computers working -for a while - so you can begin charging. If they’re both dead, a simple 12V boost will boot the control computer to begin charging the big battery (and hence the 12V). Beats trying to boost with 350V.
As I understand, Tesla has replaced the traditional 12V lead acid battery like in gas cars, with a small lithium battery (16V) that runs the local electronics, and will refill from the main battery as needed. This eliminates the danger that the 12V battery will die a natural death as most lead-acid batteries do. Apparenlty there are 12V Li-ion batteries that can plunk into the older Teslas to replace the lead acid battey - but as the service guy pointed out, you can buy 4 or 5 regular batteries for the price of one of those, and at 4 years per regular battery, where’s the payback?
Still takes some beefy power components. Window motors seem like they take significant power. There is not a lot of difference between an inductor and a transformer. Maybe high voltage capacitors are more available than they were back in the day but you will need a big one.
DC-DC converters are the magic sauce in a lot of power electronics now. The huge win comes from switching devices with very low forward voltage drops and the ability to preserve these low losses at relatively high frequencies.
Gallium Nitride and Silicon Carbide are the magic semiconductor materials. Compared to switching devices of old they dissipate a tiny fraction of the power for the same current delivery. Both because of an intrinsic low forward voltage drop and an ability to switch on or off very fast spending little time transitioning between where losses are higher.
This ability to switch at high frequencies makes the transformer or inductor tiny. The power capability of a magnetic component is limited by the ability of the device to cram magnetic field into its core. In order to cram a lot in one uses materials with a high magnetic permeability. The down side is that these all have a maximum field density they can support before they saturate and cannot support any more. The faster the magnetic field changes the more power is transferred. Thus power is limited by the cross section area of the core and the operating frequency. Double the frequency and the core area halves for the same power. A transformer running at mains frequency is ridiculously huge compared to one running at 100kHz for the same power delivery. (At the consumer level you will see little portable USB-C chargers for sale that seem impossibly tiny - possible because of GaN switching devices.)
The same architecture and technology is also what enables EV motor controllers to be small and efficient.
Inductor versus transformer coupled can come in part down to safely. A transformer gets you a fully isolated system. Faults might kill the device but they are unlikely to connect sensitive devices (such as humans) to mains or high voltage DC battery systems. This is generally considered a good thing. Doesn’t mean everything you buy is this safe. Which isn’t good.
People focus on the battery technology in EVs. But there are other technological miracles making it all work.