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Tesla shares 48V architecture with other automakers

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Re: Tesla shares 48V architecture with other automakers

#341

Post by LoganDark »

kalleboo wrote: post #259
bigdict wrote: post #256

Earlier quoted context omitted.

Dumb question but why does deciding to run at a higher voltage decrease the amount of wiring necessary? And why not increase it even further then?

Watts = Amps * Volts (or, more scientifically, P = I * V) If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt. It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed. I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actua…

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you?

What exactly is magical about higher voltages that makes them suddenly able to carry more power across the exact same wire? I know you just said it's "lower amperage" but I don't understand how amperage can be the only thing dictating the required size of a wire.

Re: Tesla shares 48V architecture with other automakers

#342

Post by Moto7451 »

grecy wrote: post #223
Moto7451 wrote: post #189

Audi also has a 48v architecture in use for mild hybrids like my SQ5. This is an older article but explains it well https://www.greencarcongress.com/2017/06/20170602-audi.html My 2021 is fully 48v except for an inverter for necessary 12v circuits (like cigarette outlets and the jumper pins) and a small motorcycle battery that is used for minimal 12v functionality. The mild hybrid battery is under the rear seats and s…

> This is an older article but explains it well https://www.greencarcongress.com/2017/06/20170602-audi.html From the article: > The 12-volt system is connected to the main electrical system via a DC/DC converter > Audi also offers the new MHEV technology with the conventional 12-volt electrical system > 48-volt vehicle electrical system. In a different layout—without MHEV—the 48-volt constant voltage system already e…

At least in the case of Audi it is more than just the starter used for the mild hybrid depending on market and configuration. On my generation/configuration of car it is also used to prespin the Turbo to avoid lag, it powers the active magnetic suspension, the AC compressor, and the power steering pump (annoyingly located between the feet of the driver and the seat where you can feel it when it runs).

While you’re right on the accessories voltage, In other comments I’ve made the point that I’m not trying to say anything about the merits of 48v accessories. Jim Farley and Elon’s bromance aside, the tech exists within car companies. It’s nice they shared but it’s not like NACS where a real issue is being solved. Problems of driving aren’t solved with 48v interior lights.

Supply lines are a real challenge and why my Audi still has 12v heated seats despite having a 48v system available. The head unit is 12v. I’m guessing the speaker amp is 12v even though 48v would make that less challenging. They have a 12v only model that shares parts and they apparently didn’t want to move everything to 48.

Re: Tesla shares 48V architecture with other automakers

#343

Post by ipaddr »

arcticbull wrote: post #193
ipaddr wrote: post #173

Earlier quoted context omitted.

He said "Journalism". A non-journalist can produce material that can be considered journalism. A student can teach. A homemaker can even write working code. The labels we give to others to divide us

> The labels we give to others to divide us Labels are an optimisation, an imperfect shortcut. They are a way we represent ourselves to others. If you don't tell me you're an engineer, I have to ask a ton of questions to assess your area of competence and skill. If you tell me you're an engineer I can save minutes or hours by putting you in a rough box. If that box is unnecessarily constraining it'll become clear as…

When race, gender, sexuality are involved we agree that labeling to save time isn't something accepted. For all of the reasons why shouldn't label those groups applies other labeling.

Re: Tesla shares 48V architecture with other automakers

#344

Post by eglretgj »

yinser wrote: post #39

I liked the interview with auto engineer Sandy Munro discussing the change https://youtu.be/ADwGGEj8sqQ?si=qp6akvy1yyWPTYNe - moving the voltage up means you can drop current - increase the data rate by using ethernet and PoE - using ethernet and PoE means you don’t have to run one off wires to each device, they can share a bus which results in half the copper being used in a lower voltage car - moving the voltage up…

I work for another EV manufacturer. Good God I would love to switch from CAN to ethernet. We already have way too many CAN buses and we're considering adding more. But it will take decades for our suppliers to even consider the switch. We just paid Bosch $15M for an upgrade to our brakes, they promised the change in six months, it took them two years and quite a few additional millions of dollars, and it's filled with bugs. We can't even run the new brake firmware on public roads it has so many bugs. And we'll have to pay them millions more and wait months or years more for them to fix their own mistakes. This is why Tesla does almost everything in house. I wish my company had the resources to.

Re: Tesla shares 48V architecture with other automakers

#345

Post by niemandhier »

eternityforest wrote: post #176
ipaddr wrote: post #173

Earlier quoted context omitted.

He said "Journalism". A non-journalist can produce material that can be considered journalism. A student can teach. A homemaker can even write working code. The labels we give to others to divide us

I always wondered why there's not some kind of nonprofit volunteer journalism organization you can get involved with. It doesn't appear to be something anyone tries to get normal citizens into, despite the fact that we constantly try to convince people to learn other stuff with much less individual scale value, sometimes even somewhat crazy stuff like home chemistry experiments with lead salts. I always thought that'…

Because it would probably be overrun by the very opinionated.

This happens frequently with new political parties: Someone starts an organisation, it get some amount of traction. Suddenly a lot of new people join and turn the whole thing into a tool to spread their views.

AFD in Germany started like this, it almost happens to The Pirate Party, one can argue that Green Parties tend to suffer from this phenomenon.

Re: Tesla shares 48V architecture with other automakers

#346

Post by hansvm »

LoganDark wrote: post #341
kalleboo wrote: post #259

Earlier quoted context omitted.

Watts = Amps * Volts (or, more scientifically, P = I * V) If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt. It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed. I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actua…

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you…

A higher voltage system enables the same energy at a lower amperage, so constrained to wanting to do a particular thing (loud stereo, bright headlights, ...), higher voltages result in lower amperages. I'll opt to not try to explain that intuitively, hoping that somebody else chimes in.

For the other half, "why do amps determine wire size?" Amps are coulombs per second -- how much electrical stuff moves through a cross section in a second. The amount of heat produced is directly proportional to amperage (every bit of movement has a chance to whack into something and produce heat, and more movement per second or more seconds generates more heat). Wire size is ultimately constrained by being able to release that heat while still acting like a wire (not melting, not sublimating, still conducting, not setting anything else on fire, ...). The amount of heat released is proportional to surface area (proportional to the square root of diameter, but that difference doesn't matter a ton right now), and the amount of heat produced is proportional to amperage and approximately nothing else. The point where those two terms are equal is the limit for the system (engineers add in huge safety factors to account for conduit and insulation and other imperfections), above which your wire melts and below which it behaves reasonably. Higher amperages require higher surface area to release the extra heat (so much higher thicknesses), so a given amount of power (stuff you want your electrical system to do) requires lower amps or thicker wires to work appropriately, because you can achieve the same power by increasing the voltage on the same amperage, thereby solving your power problems without extra heat.

Re: Tesla shares 48V architecture with other automakers

#347

Post by kukkamario »

LoganDark wrote: post #341
kalleboo wrote: post #259

Earlier quoted context omitted.

Watts = Amps * Volts (or, more scientifically, P = I * V) If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt. It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed. I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actua…

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you…

The power loss by the resistance scales in the square of the current and linearly to the resistance. So doubling voltage reduces resistance power loss to one quarter so you could lower wire size and increase its resistance to double and still resistance power loss would be halved

Re: Tesla shares 48V architecture with other automakers

#348

Post by [deleted] »

loufe wrote: post #320
kalleboo wrote: post #259

Earlier quoted context omitted.

Watts = Amps * Volts (or, more scientifically, P = I * V) If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt. It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed. I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actua…

Resistance is proportional to the square of current. This would mean 1/16th the loss instead of 1/4th.

[deleted]

Re: Tesla shares 48V architecture with other automakers

#349

Post by 15155 »

myself248 wrote: post #168
Tuna-Fish wrote: post #108

Earlier quoted context omitted.

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…

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 millio…

> 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?

Re: Tesla shares 48V architecture with other automakers

#350

Post by TheLoafOfBread »

thepasswordis wrote: post #276
TheLoafOfBread wrote: post #109

Earlier quoted context omitted.

> using ethernet and PoE means you don’t have to run one off wires to each device, they can share a bus which results in half the copper being used in a lower voltage car You mean like CAN bus is being used since 1990s? I think that Mr Munro little bit fell asleep and missed whole CAN bus and FlexRay evolution in cars.

CAN bus is still really slow (1Mbps, so bus contention is a problem). Sensors, cameras, AV stuff, etc. can't all live on the CAN bus. Cars are not the same things they were in the 90s.

CAN bus is multi-master access with automatic arbitration between nodes. Something what Ethernet is completely incapable of and that's the reason why CAN bus is here to stay for a long time.

Ethernet needs active switches isolating each branch of the star network from each other. Because Ethernet working in bus mode is absolute joke, slower than CAN bus if you add enough nodes to such network. But when you need to drag all sensors and ECUs to a center of a star where is switch, where is the saving on cables?

Even worse, there is no guarantee that node on such network will be able to deliver message to other node, thanks to CSMA/CD which says Random disconnection if collision. Well guess what? Your wheel just locked during braking and we need to tell that to ABS/ESP unit. When using CAN you can rectify it by using low CAN ID and thus increasing priority in arbitration. When using Ethernet, you are only praying to RNG Jesus.

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