Hold on a second...4x the voltage means you only need 1/4th the current. The power loss in the wire is current^2 x the wire's resistance, so 1/4th the current does indeed mean 1/16th the losses.

But 1/4th the current means you can use a higher gauge wire. Looking at a table of wire gauge current capacities it looks like if your maximum current is 1/4th you can switch to wire with 1/4th the cross section. And resistance is inversely proportional to cross section, so 1/4th the cross section means 4x the resistance.

Doesn't that then bring the savings down from the 16x you would get if you just upped the voltage down to 4x?

There's also a minimum wire size, based on physical durability requirements. A significant number of wires in the harness already carry no appreciable current and are merely signaling wires, but they can't be infinitely thin.

Getting most of the power wires down into the range of signal wires is a huge benefit, because it means they can use common terminals and smaller connectors, but that's where it stops.

For very low current wires, I've seen non-metalic (nylon?) strands woven in with the copper for mechanical strength.

Yes, typically the savings would be in the weight and physical size of the wiring harness (as well as possibly allowing for tighter bend radii). You'd design for a max amount of heat generated by the wiring harness, or possibly a max voltage drop if that's a constraint. You don't need to do heat dissipation calculations yourself, there are standards like SAE AS50881 that do the heavy lifting for you.

Edit: Smaller wire is also cheaper of course. That's probably a pretty significant upside when talking about a mass-produced vehicle.

Good point and you're not wrong. One mitigating factor is that resistance isn't constant: In copper it increases with temperature, and I^2R causes temperature to go up, which causes resistance to go up, and you get something of a positive feedback loop. Temperature rise is one of the main reasons why standard wire gauges are specified the way they are.

If you use 4x higher voltage, the temperature rise is much less significant (16x less significant to be precise) so it becomes more or less a non-issue and you can treat resistance as a constant.

> Or can and power over twisted pair.

I was reading an anti-Musk subreddit over on Reddit and I think the cybertruck is doing this? They were mad that the cybertruck uses 48V and Ethernet cables, but to me, that seems perfect for CAN and power. We already use 48V (or similar) for PoE, and CAN needs a twisted pair... so why not buy that off the shelf instead of using a custom wiring harness?

I don't think the cybertruck is a particularly attractive vehicle, but I also don't think they're crazy for trying that. You can do 10Gbps over a cat-6 cable and it works great. So I'd expect that you can easily do CAN.

Didn’t read the article, but Musk mentioned in an interview yesterday they are specifically not using CAN and are using Ethernet. He didn’t explicitly say, but it seems likely they are using PoE, saving a lot of wiring as you can daisy chain a higher bandwidth connection and you don’t need separate power cables.

https://youtube.com/watch?v=ky1Z2klPalw

Musk has publicly stated that CAN is too slow for modern cars, which is why they chose ethernet for the Cybertruck.

https://youtube.com/watch?v=ky1Z2klPalw

CAN buses run into bandwidth issues at some point. Just remove all the OTA, car-as-a-service and de-facto surveillance crap, and one should be able to get away with CAN buses.

Nothing wrong with ethernet, but listening to Musks statements, especially in fields I have some not even deep knowledge, alwqys like listening to a very confident, but otherwise clueless, 1st semester student selling you semester 2 basics as the latest and hottest shit under the sun nobody else even considered possible so far...

The question is do you want to have something that is high performance or something that you 'can get away with'.

We get it, you don't like the features of modern cars. Well sure if they built the car you would like, then CAN bus is fine. But that's simply not where the future is going, if you like it doesn't matter. Its simply not relevant when car CEO discuss what is needed for modern cars.

You solution of 'just remove X,Y,Y features' is just a laughable suggestion here. Its like saying 'you don't need a new graphics card', I play 'Star Craft: Brood War' just fine. Ok I agree, I don't play AAA games either but to criticize a Nvidia CEO for saying the need higher performance would be totally absurd.

Cars will get more electronics parts, more cameras, more safety equipment, more communication and so on and so on. Moving to higher voltage and PoE is simply a logical thing to do given that reality.

If Musk is so utterly clueless, what of the things he said is actually wrong? Musk even literally said its not 'hot shit', its just bringing things up to date. But that's the simple facts of the automotive industry, lots of 'we did it because we have always done it' and despite it not being 'hot shit' its really hard to change.

So in the automotive industry, such changes are great because if you are building millions of something, it makes a very bit difference.

Seems to me you are reading into it what you want to read into it.

Yeah, Elon talked about this in his latest interview with Munro. It seems that they just use Ethernet rather than CAN bus.[0]

[0] https://youtu.be/ky1Z2klPalw?t=791

Have a reddit link?. Search didn't help

Tesla didn’t invent 48 volts either. The EV and hybrid electric world were talking about 48 volts when Musk still worked at PayPal, if not earlier.

One of the examples pulled out at that time was that you could shave a couple pounds of copper off the alternator by running it at 4x the voltage. Much thinner wires.

Tesla's greatest innovation is simply leadership. Everyone knew castings were the way to go, but noone did it. Now people like Volvo are doing them, and I expect a lot of others to do it as well.

Everyone knew that 48V would be a big benefit, but noone did it.

TBH, in a few years, we may be saying similar things about drive-by-wire without a mechanical backup. But it is too early to say definitively.

The mechanical backup for a drive-by-wire system is different to all those other things in that it's a critical safety issue. If _anything at all_ happens to the electronics while driving then it's important that you can stop the vehicle safely. That mandates manual brakes and steering, even if they're barely effective at all without power it's a lot better than nothing.

The cybertruck has two separate steering motors for redundancy. Passenger jets have been doing "x-by-wire" for decades. Properly engineered it's as reliable as mechanical linkage.

Two motors is great and all, but that only provides motor redundancy and won't help if something happens to the electrical system.

Planes are fly by wire but that's because they literally have to be, no amount of gym time will let you move the rudder on a 737 by hand.

The 737 is not fly by wire.

Ok fair enough, it is hydraulic assisted instead but for the point I'm trying to make it's essentially the same thing in so far as it requires power.

I tend to agree, TBH. People bring up fly-by-wire, but even that is simpler. AFAIK, those systems aren't variable ratio the way CT is. CT literally will have different steering ratios depending on the speed, so one steering wheel angle will have different effects on the actual steering angle depending upon the speed.

How will that work in the real world? Could there be bugs? Will people get used to it or will it lead to mistakes?

I'm looking forward to getting a chance to try it, TBH.

I hear it’s kind of a pain in the ass to do a front end alignment on the drive by wire systems.

What everyone was waiting for was for Italians to make the huge casting press so that castings could be done in mass production at automaker margins.

Despite Tesla's boastings, large casting machines have existed before. Automotive use is the new part.

Essentially it was question casting of this size being automated at car maker scale. Bigger castings were integrated before on assembly lines, but at higher costs and complexity before Italians made the large mostly automated caster that Tesla called GigaPress (iirc) - it's essentially COTS factory equipment.

What's actually new and interesting here is the combination of size and speed. Sure casting existed, but for it to be the backbone of a super fast production line like that of a Model Y, they needed to do a lot of work.

Larger parts were often dipped into liquid, because air cooling resulted the part bending.

Tesla internal materials team worked on new alloys to improve this, while working in coordination with the machine manufacture to get up the cycle times.

And they are continuing to work with them. Tesla is using newer more advanced cooling systems in Texas then they did in the California factory. Because cooling is one of the limiting factors in Cycling these machines.

Except it was Tesla that went to the Italian casting press manufacturer and the made it a project together. Tesla asked for the biggest they had and asked for bigger and basically bought 5 years of machines, allowing them to do the necessary investment. And Tesla also used its own internal materials team to develop alloys to optimize the process to make it practical for high volume production lines like Model Y.

> Everyone knew castings were the way to go…

The jury's still out on whether gigacasting is courageous, or just moves costs from production (which will not be passed to consumers) to repairs (which will).

> Everyone knew that 48V would be a big benefit, but noone did it.

Audi did in 2016 with the SQ7 TDI, no?

Car A costs $5k less to manufacture than car B because it uses castings. Car A would be wiser to build because you can get better margins, or lower prices. It'll take a lot longer for buyers to catch on to the fact that the car costs a lot more to repair.

The question is really if the castings result in more cars being written off as total loss. Any collision severe enough to damage them would likely be severe enough to also total out a car without them as well.

TBH, the repairability concerns seem to be overstated so far. There are still conventional crash structures in front of and behind them. It takes a lot to damage the casting beyond repair.

You are right, though. The jury is still out in that they haven't really been used in the real world for long.

> Audi did in 2016 with the SQ7 TDI, no?

I didn't know about that one, but it was still a dual architecture. Going full 48V is a bit different, assuming Tesla really did that.

Clearly no MGB fans at Tesla. The unibody is cool unless you live somewhere with snow, and then rust doesn’t just make your car ugly, it makes it unsafe. And expensive to fix.

Which is why I was always more of a Triumph fan.

>> Tesla's greatest innovation is simply leadership.

Totally correct. We were making 48v power steering systems 20 years ago for OEM development projects. They simply don't have the will/commitment/leadership to bring change like that to market.

Elon sets a direction and people go that way. I can imagine someone at GM listing all the obstacles as a reason they can't change, and Elon looking at them and saying "no, you're the obstacle" or something like that.

Sure, people have been talking about 48 volts for the past 30 years. Somehow most automakers didn't actually manage to do it though.

Sandy Munro just did an interview with Musk, who said they hadn't done anything revolutionary, they just built the car up to general 21st century standards.

> The EV and hybrid electric world were talking about 48 volts when Musk still worked at PayPal, if not earlier.

You are confounding the two electrical systems in an EV or hybrid (or mild hybrid).

One is used to drive the wheels - these are very commonly 48V in a mild hybrid and something like 200V or 400V or 800V in an EV. This is only used to power the wheels - nothing else.

The other electrical system is used to power literally everything else. The infotainment system, heated seats, power windows, lights, powered seats, electric power steering, electric assist brakes, etc. This has always been 12V in every car ever ^ (ICE/hybrid/EV) (including every Tesla).

The Cybertruck is the first vehicle ever to move the 12V system to a 48V system.

^ Before about 1955 it was 6v. The move to 12v then was the last time it has changed.

I’m talking about the same thing. Pumps and compressors and electronics systems.

You're talking about some of the things that would be on the accessory belt (serpentine belt) on an ICE, that need to keep spinning even when the ICE is off (power steering, A/C, etc.). That is a slightly more fancy engine start/stop.

You are not talking about high current devices like heated and cooled seats, defrosters, infotainment and audio amps, power windows, power seats, lights, etc. etc.

Automotive Ethernet is not 8P8C...that's not how they do it at all

Some cars even use optical networking between the front and rear of the car. I think a bit of that has gone away now that you don’t need a DVD full of map data in its own module in the trunk.

You don't need it for the DVD anymore, now it's the zillions of cameras instead. The IEEE recently standardized automotive (= single pair) multi-gigabit ethernet (2.5/5/10GE) in 802.3ch…

If you go to a higher voltage, you will typically use smaller wires.

The great thing about PoE standards is there's so many to choose from. https://en.wikipedia.org/wiki/Power_over_Ethernet#Standards_...

Honestly, ethernet introduces a degree of non-determinism with respect to time in the link layer, plus increased bringup times, a potentially more costly core switching fabric, and the need for critical revision of latency assumptions on any potentially safety-related control concerns. Also, max current is not high. I would wager these are the reasons it won't be rushing to an EV near you... it's basically only suitable for a subset of uses, and heterogeneous infrastructure costs more in design, installation and maintenance cost than it nominally saves in production volume standards alignment and HR familiarity. (Source: Mechatronic systems design for the last ~8 years, IANAEE)

Regarding deterministic latency, the Time-Sensitive Networking (TSN) [1] set of IEEE standards address this. The IEEE P802.1DG project [2] in particular defines a TSN profile for automotive.

[1] https://en.wikipedia.org/wiki/Time-Sensitive_Networking [2] https://1.ieee802.org/tsn/802-1dg/

> The great thing about PoE standards is there's so many to choose from.

There is nothing to choose there. They're supersets of each other with increasing power budget, each including the previous revision as lower power classes.

(and PoDL is not PoE; PoDL is for automotive ethernet, which has nothing to do with the RJ45 you see everywhere on consumer/business IT. You never choose between PoDL and PoE, the choice is made when you decided between Xbase-T vs. Xbase-T1.)

> ethernet introduces a degree of non-determinism with respect to time in the link layer

That's what TSN is for, cf. sibling comment.

> plus increased bringup times

That's generally an IP problem, not Ethernet.

> a potentially more costly core switching fabric

I guess it depends on your application; a TSN-capable 8-port automotive ethernet switch is $10: https://www.digikey.com/en/products/detail/microchip-technol... (non-TSN non-automotive is cheaper…)

> heterogeneous infrastructure costs

Automotive ethernet is supposed to replace CAN and the various heterogeneous higher-speed interfaces that were added to deal with higher bandwidth requirements with a homogeneous ethernet world :)

(Source: I work on some software remotely related to some of this shit. Which does mean I'm biased since I don't know whether it will in fact proliferate, I just make it work ;)

Sure. It's also not like there are many ready made devices that are already available for PoE that could be useful in automotive industry.

I guess my main thought was that going to 48V and in the world of low power LED lights and such, combining power and comms into same wires/cables is something that might be appealing.

Automotive ethernet over copper physical layer is completely different than commercial/data center ethernet. It is defined in 802.3ch for multi gigabit (2.5, 5 and 10 Gbps). It uses single shielded twisted pair cables up to 15m long. Cables and connectors are automotive grade.

The power over data line (PoDL, automotive Ethernet equivalent of PoE) is defined by a separate IEEE protocol and its critical specifications like EM emissions tests, ESD tests etc are supplemented by documents created by a consortium of car, electrinics, comnector, cablr and semiconductor producors called OPEN Alliance: https://opensig.org/ . There are parts available for PoDL. The voltage levels from 6V to 60V with 6V increments are supported.

Source: I design both data center and automotive Ethernet chips.

Historically and increasingly, automotive grade electronics are a separate genre to general electronics for reasons of safety.

It's less of a safety but more of a production and environmental constraints issue. Cat5 cables are too heavy for cars. Their connectors aren't made for vibration. They have a lot of emissions which is a problem for the mission critical parts (Ethernet Phy often isn't mission critical). They are expensive, which is actually the biggest reason they aren't good for automotive.

Automotive reliability is only an issue for your ABS sensor, airbag sensor etc. but these are a minority compared to what's in modern cars these days. Real driver is cost, compactness (cost) and harsh environment (temperature and vobrations) and EM emissions. It mainly adds to qualification time, but actual semiconductor design cycle isn't that long. That being said, data center stuff is also notoriously slow to qual.

Ethernet is already used to transmit radio signal over fiber which requires extremely tight variation in latency (probably more strict than automotive).

I actually run Poe in my car to power a mini pc in the trunk. I guess I’m ahead of the game :)