[intrepidhero]

Why would a car need a 48V system for accessories? In general the things a car's 12V system powers have gotten less power hungry over time (LED's, heat pump) and in particular, an EV loses the highest power electrical device on the 12V bus, the starter. The typical equipment used for the entertainment and control systems are going to be much more available with 12V supplies, just because that's the industry standard.

Obviously the traction system is using much, much higher voltages.

The article cites "complexity" of the wiring harnesses, which is nonsense. The wires might get a little smaller, but not by a lot. Like I said, the 12V bus in an EV isn't driving a bunch of high power stuff. (Is it? Am I missing something?)

The one place I can imagine it helping is for driving inverters so you can provide AC outlets for laptops, power tools, etc.

[myself248]

Hi, automotive electrical is my job.

There's quite a bit of very thick wiring in a car, not just the starter wire, but boring stuff like audio amplifiers, rear window defrosters, power seat motors. Those things don't draw a ton of power, like maybe just a few hundred watts, but at 12 volts even modest powers require extraordinarily thick wires, especially when you account for bundle derating.

This requires large terminals, which requires larger connectors, and there's the complexity, because MOST of the wiring in the car is just signals, or low-power stuff, which can run over thin wires and small terminals. (Minimum size is limited by mechanical durability rather than electrical conductivity.) Making a "hybrid" connector that has a couple large cavities for large terminals, and a bunch of small cavities for small terminals, is a pain. Having separate connectors for heavy power and for signals introduces more assembly work and negatively impacts testability. The wires have different stiffness and bend behaviors, they exert different amounts of force on weather seals, they have to be terminated on different machines at different points in the assembly process.

By allowing power wires to be nearly as thin as signal wires, you can use simpler connectors with unified terminals. Manufacturing gets simpler, harnesses get lighter, assembly gets faster and easier.

Weight is also a huge deal, every ounce counts. There's upwards of 100 lbs of wiring harness in most cars, more in larger or premium models with a lot of accessories. If half of that weight is signals and won't change with voltage, but the other half is heavy power circuits that'll get 4x thinner at 48v, it's significant weight savings.

Furthermore, switching heavy current means massive relays or FETs and the heatsinks thereon. If you can reduce the current, those components get lighter too. Audio amplifiers get lighter, speakers get lighter (stupid heavy-wound 2-ohm speakers to get reasonable volume out of low voltage drive? Nah, use standard 8-ohm now that you have real voltage at the amplifier!), all sorts of things get lighter.

That's all in addition to the electric power steering already mentioned by others. EPS can easily move 1kw for short periods, and has stupidly huge wiring to do that at 12v. It's still chunky at 48v, but a lot less so, and can use more common terminals and connectors. Replacing a hand-assembled bolted connection with a machine-crimped and clicked-together connector improves reliability or reduces testing process overhead.

It's really significant, and it's embarrassing that the industry fell flat on its face in the late 90s last time they tried. Here's hoping this takes off.

[Tuna-Fish]

And to explain why this hadn't been done before/how we got here:

Nothing in a car actually wants 12V DC. Most of the low voltage stuff will run better at 5V or below, while a lot of the higher voltage stuff would benefit from going as high as possible. 12V exists because DC-DC conversion used to be expensive, and you had to make a compromise about the voltage based on losses, wire thickness, and picking a low enough voltage that all the low-voltage stuff doesn't suffer too much.

What's changed is that you can get a single-device DC-DC converter for really cheap these days. Cheap enough that you might as well put it in the light bulbs, and everywhere else that wants a low voltage.

[myself248]

12v exists because 6v was too low; wires were impractically thick for even the early accessories being added in the 1950s. The 6v-12v transition happened in 1955/56 for many cars. Some stuff like lightbulbs could be reused by putting two 6v bulbs in series in a 12v car, so it was a very cheap and relatively straightforward transition.

If they'd just had some foresight and gone 48v in 1955, we would've saved 50 million tons of copper in the years since. It's no harder to make 48v motors or lightbulbs or relays or anything else (and in fact, the telephone network contains plenty of exactly those things, and has, in staggering numbers, for over a century), but the automotive industry isn't exactly known for being forward-thinking.

[robocat]

A 12-volt battery typically has six cells. A 48 Volt Lead-acid battery would have 24 cells - I'm not sure how that would change the constraints on charge balancing and starter-motor stress.

I can say that the 24 Volt deisel vehicles I have used makes buying two batteries expensive.

[15155]

> If they'd just had some foresight and gone 48v in 1955

How would they have done this without cheaply-available high-speed switch-mode power supplies with low-DCR inductors/MOSFETs?

[myself248]

Why would they need those?

All the stuff that's natively 12 volts now could simply have been made natively 48 volts. You can make a 48-volt lightbulb as easily as a 12-volt lightbulb. You can make a 48-volt motor as easily as a 12-volt motor. Actually, motors for higher voltage tend to be smaller and lighter, which is why industry tends to go straight for 4160-VAC motors whenever 480VAC is inadequate.

What applications cannot be made to work at 48? I'm not aware of any. As I said in the comment to which you're replying, the telegraph and later the telephone network had been running similar DC systems since the 1850s or so at various voltages depending on the length of the telegraph line, with the telephone network taking over and 48 volts firmly entrenched by the 1910s. There was a huge manufacturing base producing 48-volt equipment, including motors and generators, indicator lamps, and a mindboggling array of switches, relays, stepping selectors, and their ilk, and all that was before WWI.

Furthermore, Charles Kettering who invented the automotive starter motor (and made it work at 6 volts), was around the same time making Delco-Light plants for rural electrification, which mostly ran at 32 volts DC. These supported a whole line of 32VDC appliances -- lights, vacuum cleaners, kitchen gadgets, irons, motors that could be attached to other machines in the shop. There was also a less common 110VDC version of the system but I can't find any contemporary literature discussing the differences, although I'm sure they would've quickly discovered that the 32V system was pretty docile while the 110V encouraged extreme care around open contacts.

As for why cars didn't use the higher voltages already in use and superior in many ways, my only guess is that a lead-acid battery with a high number of small cells must've been difficult or expensive to manufacture, compared to one with a small number of large cells. The Delco-Light plant used a large rack of 2-volt cells, whereas the starter motor used a single 3-cell packaged battery that fit easily under the hood. If they'd just figured out how to package more smaller cells together....

[15155]

> Why would they need those?

To convert voltages to useful levels without suffering massive losses in efficiency.

> What applications cannot be made to work at 48?

Basically every logic-level transistor will not work at 48V. It's nice that these last-century analog devices could be made to operate at different voltages: present-day semiconductors are not so conveniently flexible.

Simple physics dictates that required inductors to step between voltages increase in physical size (and weight, and material cost) as that voltage disparity increases. Capacitance required, etc. all increases with it. Efficiency plays into both of these as a triangle. Heat increases as this disparity increases. These properties are unacceptable for a myriad of use cases.

[elihu]

I think another big part of it is that DC switches tend to get expensive above 12V. Cheap AC switches work fine at higher voltage, because the arc is self-extinguishing as it passes through zero twice per cycle, but DC doesn't do that so you can end up with an arc that doesn't extinguish itself, which, aside from not turning the thing off when you want to, burns out the electrical contacts.

[dreamcompiler]

Now we have MOSFETS and IGBTs that can switch DC without sparks. I suspect most DC switching in the Cybertruck is relayed through these. (Except the main contactor and pyro fuse of course.)

[myself248]

And the contactor is usually switched with no current through it. The only time it would open under load is in an emergency, and presumably it only does that once.

Which is to say, yeah, it's a non-issue for pretty much everything. Even in the 12v realm, new BCMs have so few relays anymore, almost everything's done with onboard FETs and software.

[elihu]

And given that this is a Tesla, it wouldn't really have had many mechanical switches in the first place. Maybe the turn indicator? Which could happily run at 5 volts or something and blink the lights via CAN bus messages.

[Kirby64]

None, unless you count the physical buttons as 'mechanical switches'.

The turn signals on a Tesla don't even make the 'clicking' noise if the Infotainment is rebooting, because it's literally just a noise piped through the infotainment.

[carabiner]

Have you been able to look at the Tesla document? Do you think it'll meaningfully help the EE's at other automakers redesign their architectures?

[panick21_]

Awesome to hear from an expert. Im looking forward to some teardowns to see how the set this all up.

[sowbug]

Thanks for this detailed answer. The chassis is normally grounded. Has anyone tried sending a positive charge through part of it? Combined with a Powerline-style signaling system, some components wouldn't need wires at all.

I already can think of several reasons why this wouldn't work, but I wonder whether there's a good idea in there somewhere.

[mcguire]

The rumor I heard was that the higher voltage resulted in lower switch lifetimes. Any truth to that?

[tgsovlerkhgsel]

Would there actually be switches switching 12 or 48V in a modern car, especially a Tesla? I'd expect the switches to only switch signal voltage/current, and power electronics (MOSFET? no idea, not an electrical engineer) switching the actual loads.

[stephen_g]

That's right, the switching concern was in older cars where they were switching the 12V straight up, so that is a reasonable point for why they never switched to higher voltages, but yes, in most modern cars (and basically all EVs) buttons and switches would mostly all just be signalling electronic units to do the actual switching.

[cogman10]

Yes, but not meaningfully. The higher the voltage you get, the more arching there is when a relay trips (also depends on if there's any sort of inductive load, think the sparks you see when you unplug a vacuum without turning it off).

But when you think about the impact that has on switches and relays, realize that in your own home you have 120V controlled by switches. Very cheap switches last decades (though admittedly not switched as often as something like a blinker).

[myself248]

Ahh, no.

AC is fundamentally different from DC when it comes to arcing behavior, because it has zero-crossings. If a switch arcs while switching AC, the arc goes out 1/120th of a second later. An arc would have to be pretty enormous to have enough thermal mass to remain ionized long enough for the next half-wave to re-energize it and sustain it. (HV AC transmission and distribution tends to have SF6-filled switches for this reason.) But around the house, your AC switches are really simple because they're not moving anywhere near that much power. And statistically, some fraction of switch openings happen with near-zero instantaneous current anyway.

DC, by comparison, is brutal to switch. It doesn't have zero crossings, so the arc has to be blown out by the design of the switch. That means nice wide contact openings, and on really large ones, magnetic blowouts to divert the arc into chutes that cool it.

If you look at a switch datasheet.... pulling up a randomly-selected one from Digi-Key now.... https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus...

Look at the cycle ratings. It has a bunch of different ratings depending on the contact form (some that're forced apart, some that're sprung apart), but in all cases, the DC rating is equal or much lower current than the AC rating. And the DC ratings only go to 24V, this switch IS NOT RATED for use at 48VDC at all, despite happily going to 250V when switching AC.

So, if you're comparing apples to apples, if you had 48VAC for instance, that would be easier to switch than 120VAC. (At constant current, that is. If you want to move the same power, you need more current at the lower voltage, and it gets harder again.) But DC is oranges.

Yes, switching 48VDC is harder than switching 12VDC, but only at constant current. And it may require _different_ switches than 12VDC. Given that you only need a quarter as much current to move the same power, it's still a net win, but it's not at all comparable to switching AC.

[Kirby64]

You're correct in all of that in regards to mechanical relays, but none of this matters for solid state devices. I'm not aware of any actual mechanical relays in Tesla's. They do have contactors for the HVDC connections, but that's about as close as you get to relays. Hell, they don't even have fuses; they use self reset-able 'soft' fuses.

You have to worry about shutting down current quickly (i.e., inductor flyback), but that's a pretty trivial problem to solve.

[mcguire]

I thought about those, but the 120v AC switches are gigantic beefy things compared to most automotive switches.

[tootie]

Is Tesla's design here actually innovative or really just they're the first ones to put together a bunch of stuff that everyone knew and hasn't had the wherewithal to implement?

[ricardobeat]

> or really just they're the first ones to put together a bunch of stuff that everyone knew

Thats what 80% of “innovation” is, with the exception of applied science fields.

[stephen_g]

I've been in the telco/digital communications space for years and all this stuff has run from 48V for decades. So basically plenty of electronic parts are already available with margins suited to 48V already since it's extremely common in other industries like the one I'm in.

Automotive just tends to be a pretty slowly changing industry, but everything is ready for them to adopt 48V that other industries have been using for a long time, someone just needed to take the plunge I guess.

[myself248]

I haven't seen the document being referred to elsewhere, but I highly doubt that there's anything fundamentally new under the sun. The industry tried this before but got stuck in a first-mover-disadvantage situation, which doesn't affect Tesla as severely because they have relatively few parts in common with other cars in the first place.

So put me down in the "wherewithal" column.

That's not to discount it at all. There are some real challenges; most automotive fuses for instance, are only rated for 32-volt operation. (Fuse voltage has to do with the length of the gap opened when the element blows, and the structure's ability to withstand or staunch any arcing that may happen.) Telephone fuses would work here but they're not exactly cost-optimized, I'd love to see what they do in this space.

Switch and relay contacts too, may need different or thicker coatings to reliably break 48 volts at the number of cycles needed, but they'll be doing so at much lower currents so I think it's a net win. (Contact wear isn't my field of expertise, though.) However, mechanical switches are decreasingly relevant in the power path anyway, and FETs will definitely do better with the lower currents.

One thing I saw talked about last time, which is completely irrelevant now, is alternator load-dumps. You know, due to the lack of alternators. But in the past, with an accessory belt spinning an alternator, the power produced by the machine was dictated by the current in the field winding. Regulating the output was a simple control loop, sensing the system voltage and servoing the field current accordingly. The field winding has significant inductance so its field can't change quickly, but with a big battery sitting on the bus that didn't matter. However, if the battery lead became disconnected, and the power draw on the system decreased, the alternator would suddenly be producing too much current and unable to rapidly reduce its field, and with no battery there to absorb the overage, the result is the system bus voltage spiking as high as 120 volts, or at least that's what the load-dump test spec says you have to withstand for 400 milliseconds. In practice with incandescent bulbs and some other linear loads around, they'll typically clamp the transient to 40 volts or so, but that's still pretty harsh for stuff that's working at 14-ish.

The concern was that a 48-volt alternator could produce some truly terrifying load-dump transients. (Although I think this is also overblown; it's running at lower current so the field winding would be weaker and should be able to decrease its field faster, no? Hmm. I should do some math...)

But now that the 12v or 48v is produced by an electronic DC-DC converter running from the traction battery rather than an alternator spun by the engine, it's completely immaterial.

[jpm_sd]

Littelfuse makes some nice 58V rated blade fuses.

[brandonagr2]

Doing it first is innovative

[dreamcompiler]

Musk said the 48v stuff was not innovative at all; they were only doing the latter things you pointed out.

[brandonagr2]

Related to the weight of signal wires, Cybertruck also moved to using ethernet instead of traditional canbus, which significantly decreased the complexity of that harness

[jabart]

Power steering pumps are electric and have one of the largest wires in my truck. With an EV you also have a heat pump, maybe a heater, coolant pumps now that you don't a constant spinning pulley, windows, lights, headlamps, power doors, seats, radio, amplifier, small PC, etc.

From the article "Switching to 48V architecture alleviates a huge number of challenges automakers are facing with 12V. The biggest one, though, is complexity: You need far less complex wiring harnesses to power all your vehicle systems"

My take is that 12v requires almost a dedicated power line for each part, while a 48v could run to a bus line that gets tapped. 48v might be something that divides easier with the battery pack, and drops the 12v battery.

[intrepidhero]

I hadn't connected the dots that all the various pumps (and fans) have to switch from mechanically connected to the engine via the accessory belt to electrically driven. That's a fair point.

[smileysteve]

It has been optimal to run accessories electrically for ICE already for several reasons. It has been difficult based on some of the loads on a 12v battery (agm has really helped this)

- Start stop is smoother (and more available) without accessories

- Cooling a turbo after the motor is off - true for the engine as well, heat soak on water pump off can go ~20f over the thermostat

- Brake Boosting without a vacuum (Valvetronic or Hybrid)

- Air Conditioning at idle

[lizknope]

> Power steering pumps are electric and have one of the largest wires in my truck.

Most new cars don't have hydraulic power steering systems anymore and use an electric motor for power steering. It improves fuel economy as well but the steering feel is generally worse than a hydraulic power steering system.

[pgeorgi]

https://de.wikipedia.org/wiki/Bordnetz#48-Volt-Bordnetz_im_A... explains (a bit) why German car makers are using 48V since ~2016 (in addition to the still existing 12V system, which seems to be the difference with Tesla, which went 48V-only).

DeepL translation:

The 12 V electrical system can barely cover the power consumption that modern vehicles need for their comfort systems. The "static" consumers completely overload the alternator, which provides up to 3 kW of power, especially at low temperatures.[12] The battery power is not sufficient for additional dynamic consumers, such as powerful electrically driven compressors.[13]

For this reason, a proposal was made at the end of the 1990s to install a 14 V/42 V electrical system in motor vehicles.[14] From 2001, Japanese manufacturers and General Motors launched hybrid vehicles with this electrical system on the market.[15] Although Daimler-Chrysler was one of the co-initiators of this concept, it was not used in Germany. One reason for this was that it did not appear possible to demonstrate a corresponding utility value to customers for the necessary additional price[14].

Instead, since 2010, German car manufacturers have favoured the solution of providing a second 48 V electrical system to supplement the 12 V system.[9] Since 2016, the first series applications of 48 V electrical system components have been the operation of the electric compressor and the electromechanical roll stabilization in the Audi SQ7 4.0 TDI and Bentley Bentayga. Both are based on the same platform.

Translated with DeepL.com (free version)

[intrepidhero]

A split 48/12 system makes a lot more sense. Run the heater/heat pump, power steering, coolant pump, etc on 48V and keep entertainment and controls on 12V.

[bryanlarsen]

Computer chips use ~1.5V or so these days. Why go 48V->12V->1.5V when you can go 48V->1.5V directly? If it's more efficient to use an intermediate voltage, you can choose the most efficient intermediate voltage internally rather than using 12V.

[taylodl]

Because we already have the 12V infrastructure and part supplies in place. You're disrupting things for no benefit. We've been running split 24V/12V systems for decades now in automotive applications. It's not that big a deal to change that to 48V/12V systems as many European car manufacturers have done.

[bryanlarsen]

No benefit? I've seen estimates of $1000 in reduced cost due to reduced copper wiring, and more importantly the labor required to string that wiring.

Modern phones charge on 48V these days, so 48V parts are extremely common & cheap.

[Kirby64]

What modern phone charges at 48V? I'm not aware of any that charge at even 20V, outside of a couple of gimmick devices. No Samsung or Apple phone charges at anywhere close to that, that's for sure.

[pgeorgi]

I'd fully expect other car makers to move to an exclusive 48V setup at some point. They just do it gradually: For the new model a part is replaced by its next-gen successor that is incompatible anyway? Put it on the 48V bus. Repeat until the 12V system is done away with - or force the issue when there are only a few components left, or downstep the 48V to 12V right in front of them, once that's cheaper than keeping the remaining 12V system.

[jabl]

> I've seen estimates of $1000 in reduced cost due to reduced copper wiring

What about aluminum wiring? Lighter, cheaper, though bulkier than equivalent copper. Aluminum wiring got a bad rep back in the day, but it seems with current electrical aluminum standards it supposedly works pretty well.

[taylodl]

What you may have saved on wiring is going to be offset by the increased cost of the battery (I'm seeing 2x-3x cost) and the fact you now need a much beefier alternator which is going to have its own cost.

You'd think if it were a slam dunk then the bean counters would have insisted on a transition to 48V years ago.

[bluGill]

There is a lot of off the shelf 12V equipment you can buy. Plus even more that is sitting in garages ready to be installed in the next vehicle. Cars are manufactured in enough quantity that it would only cost $0.01 per vehicle to design it (plus parts costs which are probably the same), but that is still a few million to the bottom line if they use the same 12 volt radio. Add to that that ICE cars everywhere have 12 volt starters, and you can buy 12 volt jump start kits: when (not if!) a battery fails to start the ICE you better be able to jump start it from a 12 volt battery - this is a safety issue.

Tesla doesn't have ICEs, so the safety concerns are lost on them. Thus all 48 volt makes some sense. They still need something for all the accessories people have.

[TaylorAlexander]

Why not use 48v? I have been designing my farming robot's electrical system and it all runs on nominally 45 volts. The switching power supply you need to downregulate that to 12, 5, or 3.3v (I have all three on one PCB) is tiny and cheap. [1]

No matter what voltage or power level you need, higher voltage will allow for smaller/cheaper wires and connectors that are easier to route and assemble.

[1] You can browse the Kicad PCB design directly in the browser with this handy web viewer. The power section is the top left: https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2FTwis...

[londons_explore]

Some devices in a car are still pretty power hungry. Eg. The blower motor for the fan (typically 800 watts = 70 amps @12v). Heated rear screen (240 watts = 20 amps). Window motors are pretty powerful too.

End result is you need a lot of fairly chunky cables to power those things.

And the price of copper has been steadily climbing since 1960 - unlike other commodities which have been getting easier and easier to extract with more automation in mines.

[adolph]

Here is an explainer:

https://youtu.be/ky1Z2klPalw?t=573

Transcript:

. . . a little bit about electrical electrical engineering um you don't need to know a lot but just a little bit uh we'll understand that you actually want a higher voltage in order to reduce the resistance losses.

So the heating in any wire is the current is the square of the current. So if you're trying to get a particular power rating through then as you increase the voltage you can decrease the current. Voltage times amperage equals your power. To hold power constant, the heating is is proportionate to the square of the current. So you want to raise the voltage in order to lower the current thus lower the heating in the wire.

And the net effect being that you can have much thinner wires, then as you raise the voltage you can you can drop the the the thickness of the wires. You can have much you can use much less, in a nutshell. You can use much less copper and the wire harness weighs much less as you raised the voltage.

[CamperBob2]

Like I said, the 12V bus in an EV isn't driving a bunch of high power stuff.

Take a look at the fusebox in any modern car, EV or not. (There will most likely be more than one fusebox.)

You'll see lots of 20A, 30A, 40A parts, some even larger. Running those circuits on 12 volts takes more copper than you probably think it does. More copper and beefier (read: much more expensive) connectors. The move to 48V is frankly overdue.

[PinguTS]

What many people underestimate is all the comfort stuff we have and use in modern vehicles. Most of the utilizes some sort of electric drive. Any electric drive requires power: * Power sliding windows * Power seats * Electric trunk * Power sliding roof * Electric mirrors

Also other stuff: * heated back window * heated front window * heated seats * heated steering wheel

Also the lights, even when they are LED they still draw a lot of power: * front lights, * back lights. * surrounding lights * comfort lights

That is just of few devices. Just look into all the comfort in a modern (luxury) vehicle.

[panick21_]

There is a lot more. There is a huge amount of safty equipment and sensors in modern car. That stuff that is not seen but its there as well.

[mauvehaus]

Not that anyone is going to stick a plow on a Cybertruck, but holy shit is the hydraulic pump on one of those a huge current draw. It's 4AWG wire on mine. The battery is kind of marginal[0] and when I raise the plow, the volt meter goes down to 7-8 volts if the engine's at idle and the alternator can't supply the needed current. Gunning the engine improves the situation somewhat, but wow, was that an eye opener.

[0] Everything on that truck is kind of marginal, actually. If you aren't plowing for money, plow truck is the last stop before the big parking lot in the sky.

[bryanlarsen]

Most of the residential snow clearing outfits around me use plows and blowers on Kubota tractors. Probably part of the reason is so that can use PTO hydraulics...

[bluGill]

There are pros and cons. Snow plows beat on a the vehicle - which is why plows are the last thing a truck does before you quit using it. Highway departments will use a dump truck mounted plow because the frame of the dump truck can take the beating (that they can put salt on the dump truck is a very useful side effect). Tractors are designed to pull plows through dirt which also beats on them, and so tractors can stand up to snow plows better than a truck. However tractors are slower and so cannot work for on road work. PTO and hydraulics are useful as well.

[Filligree]

You don't use custom-designed vehicles? I'm used to snowplows being these massive, reinforced vehicles that look like they could take on a tank.

[mauvehaus]

I haven't a clue what you're describing. Do you have a picture? Also: where do you live, and how much snow do you get?!

[mrep]

Not OP, but here in park city UT, we average ~21 feet of snow a season and got an epic 51 feet last season!

I normally see dump salting trucks with plows that plow/salt the roads during snow falls and then we have cat bulldozers that later come pick up the snow and move it into dump trucks to be hauled away.

Video of the cats: https://www.icloud.com/attachment/?u=https%3A%2F%2Fcvws.iclo...

[Filligree]

Northern Norway. But it isn’t snowing right now — and also I’m in Ireland — so can’t do.

[bluGill]

I've never seen that in Minnesota. They are attachments to a dump truck or road grader.

[bryanlarsen]

Yup, the tractors are for driveway work. For road work uses the dump truck mounted plows you describe.

[waterheater]

Compared to ICE vehicles, EVs are expensive and heavy (according to Slate, an F-150 Lightning weighs 35% more than its ICE sibling). Cost and weight reduction are both important factors for any EV maker to optimize.

Why do you assume the 12V bus doesn't drive high-power stuff? Historically, every single electrical component in a car is powered at 12V. Everything. Your alternator outputs 12V to both power your electrical system and charge the 12V battery. Even the starter and ignition system (distributor or coil pack) transforms 12V into the high voltages needed for combustion.

I'm not exactly sure why 48V corresponds to a decrease in "complexity." My guess is that power and data were sent over separate cables, whereas PoE does everything together. That's just a guess, however.

Assuming the same power requirements, a 4x increase in voltage translates to a 4x decrease in current. Looking at [1], a component requiring 8AWG @ 12V can now use 18AWG @ 48V. That's a significant decrease in copper, resulting in cost and weight reductions. A higher voltage is almost always preferred, though the higher electric potential means you need better insulation and safety measures.

Though there's a saying that it's current, not voltage, that kills, high voltage is widely known to be dangerous. For example, consider the US electrical grid, which is actually a 240V system, not 120V. Three wires come to your house from the transformer: -120V, 0V, and 120V. A normal outlet is connected to either -120V and 0V or 0V and 120V, and you can get a 240V outlet by connecting to -120V and 120V. This 120V-by-default setup is much safer than 240V every outlet, like in other parts of the world, and you can still get a higher voltage for high-power appliances (e.g. clothes dryer).

[1] https://en.wikipedia.org/wiki/American_wire_gauge

[contingencies]

Compared to ICE vehicles, EVs are expensive and heavy

Expensive maybe, IMHO not really, at least in China. Heavy .. this doesn't sound fair. Are you comparing a cherry-picked, heavy, full battery back EV with an empty tank ICE? Noting the EV has far more torque, and that the same tech is used in UAVs and in a ground vehicle you can arguably move the weight around (lower it) easier in an EV, this casual observer (not a car person) would expect superior mass distribution and lower overall weight (certainly vs torque).

500kg solar EV: https://www.unsw.edu.au/newsroom/news/2022/06/sunswift-7--dr... ... compare Toyota Corolla: 1314kg + 50kg fuel / Toyota Camry: 1360kg + 70kg fuel / Tesla Model 3: 1611kg / Toyota RAV4 average: 1634kg + 55kg fuel / Tesla Model S: 2107kg / Tesla Model X: 2458kg / Your cherry-picked example of an F-150 Lightning: 2948kg / Chevrolet Silverado 1500: 3311kg + 105kg fuel / way more heavier ICE cars follow...

Another potential consideration is that the EV is far better placed to use recovered power from braking, so a small amount of additional mass will have less efficiency impact than in a comparable ICE.

[stonogo]

Vehicle weight also affects how much wear the roadways experience. I'm not sure "A Corolla weighs less than a truck" is relevant here, especially considering that the F-150 is the most popular vehicle in the US by sales number. Comparing things to the market leader is generally a useful metric.

[speedgoose]

Heavy trucks damage roads much more than cars. It depends on the weight but it’s exponential. The weight difference between an EV and an ICE of the same category is not a big concern to have in terms of road damage.

https://en.m.wikipedia.org/wiki/Fourth_power_law

[rnk]

Just to add the basic idea, the amount of power is amps * volts. So to carry the same amount of energy with a higher voltage, you can you use less amps. The amount of amps impacts how big the wires are, lower amps need smaller wires and that means less space for wires but more importantly less weight of the wires. There is a lot of wiring in a car. Tesla claims this could be 1/4 the amount of copper wiring in an article, below.

This article describes a bit about this, but also says something I never heard, that there were 6v auto systems in the 1960s. https://www.mining.com/new-tesla-low-voltage-system-a-big-de...

[bokohut]

It may help some also to know what an amp actually is: 6.241x10^18 protons or electrons per 1 second of time passing a certain point. A single Amp is equal to 1 Coulomb and 1 Coulomb has 1 Joule of energy. I share this from my personal documentation in comprehension of understanding the unseen resulting from a device I am building to solve a personal energy storage problem. All open knowledge certainly but graphing these relationships into a visual depiction of the correlation has greatly assisted when talking to others that have ZERO knowledge about energy and power. Humans are nearly all 100% visual so explaining it with pictures presents A LOT of AHA moments for those without such comprehension.

The inverse relationship between amps and volts can also help: 50 volts * 24 Amps = 1200 Watts 100 Volts * 12 Amps = 1200 Watts 120 Volts * 10 Amps = 1200 Watts 150 Volts * 8 Amps = 1200 Watts 200 Volts * 6 Amps = 1200 Watts 240 Volts * 5 Amps = 1200 Watts 360 Volts * 3.333 Amps = 1200 Watts 480 Volts * 2.5 Amps = 1200 Watts 600 Volts * 2 Amps = 1200 Watts

Stay Healthy!

[bluGill]

6 volt autos were going out of style in the 1950s. They did last into the 1960s, but they were already rare by then.

[codeulike]

As well as switching to 48V they are going to use Ethernet cables for most of it (PoE). So at the same time they get rid of the CAN bus wiring and have everything running on ethernet for communications and power, which means a LOT less wiring because with CAN bus every device needs its own wire but with Ethernet its much easier to have 'hubs' that channel communications and power on to other devices.

https://twitter.com/cybrtrkguy/status/1731658374775771297?s=...

[martythemaniak]

The savings in terms of weight and efficiency are actually significant. This was covered in Tesla's investor day presentation earlier in the year:

The section on electronic architecture (~10min): https://www.youtube.com/live/Hl1zEzVUV7w?si=-Vz0gKT5YDbtrG9V...

The sub section (~4min) on 48V in particular: https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7...

[tshaddox]

> Why would a car need a 48V system for accessories? In general the things a car's 12V system powers have gotten less power hungry over time

It’s not primarily about delivering more power, is it? I thought the point of higher voltage is that for a given power the wires can be smaller.

[bluGill]

It can be both. Higher voltage allows longer small wires, and/or more power on the same wires. Depends on what the car needs. If it is just a few lights on the back of the car you are looking for smaller/cheaper wires. However if you are looking to put something power hungry in back (work trucks have a lot of needs around this) the higher voltage allows the same wires to deliver more power.

[fasteddie31003]

Anything drawing over 250 watts is going to need over 12 gauge wire. I put a 2200 watt inverter in my truck and I needed to put 4/0 gauge cables to it which are huge. 48v would mean I could have gotten away with only 8 gauge wire.

[noncoml]

One example is Porsche PDCC. It needs 48V to work so you end up with a car that has both.

Also I think all Mild Hybrids are 48V, so maybe theoretically you could get rid of the extra 12V battery there?

[bryanlarsen]

In the case of the cybertruck, the windshield wiper motor to drive that massive 4 foot wiper blade is 5hp and would require 300 amps at 12V. That's larger than a starter motor.

[bluGill]

Larger in what way? A starter can draw more than 300 amps in some cases. However a starter only needs to run for a few seconds and then get plenty of time to cool off. You can burn out a starter if you crank the engine for too long. By contrast a windshield wipers needs to run for hours when you are driving in the rain, and thus needs to be larger to dissipate all the heat. (starters are also typically series wound DC motors which are also smaller, they work great for starters but not for most other motor applications)

[SkyPuncher]

You can run smaller wires through the vehicle then down voltage on device.

[londons_explore]

Most MOSFETS are 50 volt rated. 50 volts is a sweet spot for switching the most powerful load with the smallest and cheapest switch.

[KaiserPro]

if you're switching 48v, you'd want a mosfet rated for way more than 50v. On a car you'd want 200% headroom at least.

[londons_explore]

With totally uncontrolled bus capacitance and inductance, sure.

But when you're using the same bus for Comms you need to have control of high frequency spikes, and low frequency spikes are easily handled by a bidirectional DC/DC. Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.

[KaiserPro]

> Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.

https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HD... disagrees.