Only on the cybertruck, the Y and 3 are still mostly 12v

I wonder why all electric cars aren’t designed from the start to use 48v.

Component availability mostly, the entire automotive world is designed for 12v systems.

I would not have expected many shared components between electric and ICE cars. Especially Teslas.

Not only is the majority of an EV the exact same components as an ICE car, but the electric car industry has been using off the shelf components for decades.

Tesla buys plenty of products from them, including things like electric steering assist.

Bosch wants to stay relevant for longer than ICE cars after all, and a lot of these components were developed for ICE cars anyway.

For the powertrain, sure obviously and absolutely.

But e.g. why have different electric window motors, wiper motors, turn signal solenoids etc etc?

Tesla have done a lot of vertical integration, but for other manufacturers there's a lot of common electronic components. Stuff like headlamps (even if it's a different plastic housing the board will be the same basic design), door locks, infotainment, dashboard displays where there's little reason to significantly reengineer them for an EV.

I don't think it would have to be only electric cars, if you're building a hybrid where the 12V battery is kept charged by the high voltage battery, you've got basically the same situation.

Availability of accessories seems like it would be inconvenient for any early adopters, e.g. you can readily get USB chargers, portable generators, coolers, tire inflators, battery boosters, etc. that run off 12V... if you get a 48V vehicle today, you'd either need a 110V->12V adapter to run accessories, or you'd be limited to 48V RV accessories.

What would be the exact benefit for 48V?

Virtually all electronics need a step down (buck) converters as they run at lower voltages 5, 3.3, 1.8. 12V > 3.3- 1V would a single step. 48V ones would likely require an intermediate step. The only exception would be running some power systems where it'd require less current.

You're going to need the expensive bits of a power supply anyway to meet transient requirements, so it's not much of a savings to run at native voltage and it gives a lot of design freedom/reusability to have one voltage for everything.

The main savings is current though, because the wiring harness is one of the most expensive parts of a car.

The move to 48v is very much about efficiency within the harness backbone. For the same wattage, less amperage is needed in a higher voltage system, meaning the wires can be smaller and they produce less waste heat.

There are a few different topologies for a 48v harness, but somewhere in the line there's a 12V DC/DC converter in there somewhere.

Cost.

The wiring for 48V can be a lot thinner than it is for 12V. As there is a square law involved for resistive heating it turns out that wiring for 48V can use 1/16th of the weight of copper as that for 12V.

A switchmode converter can be designed for 48V just as easily as 12V.

It's far cheaper and easier to just pluck a readily available 12V power supply off the shelf than it is to design one that will have limited applications outside of a single manufacturer.

The inertia of established supply chains and industry norms can be a real mother to overcome.

Hobbyist computing could benefit from a move to 48V as well, if only to keep the problematic 12VHPWR from killing expensive video cards.

I say hobbyist because AIUI 48v is making inroads in server hardware but that's not my area.

48v automotive designs have been available from suppliers for a few years now.

You generally can't reuse non-automotive power supplies in automotive because the requirements are very different.

Less copper and thinner wires throughout the vehicle.

12v is easier to adapt and take parts off the shelf. Remember that EVs weren't quite obviously the future at some point.

I have to wonder if this ever happened with the 6v to 12v transition somewhere in the 50's-60's

Because all of the IC's that are attached to the battery are designed for 12V. Things like solid state relays (BTS7008 for exammple) and the 5/3.3 volt regulators.

Interesting, thanks!

16V internally