9 ms·

The "expert" in the article got it wrong. The relationship between the voltage and the losses in the wires is not proportional. They are squared. Going from 12V

The "expert" in the article got it wrong. The relationship between the voltage and the losses in the wires is not proportional. They are squared. Going from 12V to 48V is not a saving of 4x rather 16x. For some applications you could also consider Power over Ethernet in the car, get both shielded comms and power. Or can and power over twisted pair.

contingencies 3y ago
The great thing about PoE standards is there's so many to choose from. https://en.wikipedia.org/wiki/Power_over_Ethernet#Standards_development 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)
- jnsaff2 3y ago
  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.
  - contingencies 3y ago
    Historically and increasingly, automotive grade electronics are a separate genre to general electronics for reasons of safety.
    - bgnn 3y ago
      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.
  - bgnn 3y ago
    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/ 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.
- rfdonnelly 3y ago
  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 https://en.wikipedia.org/wiki/Time-Sensitive_Networking [2] https://1.ieee802.org/tsn/802-1dg/ https://1.ieee802.org/tsn/802-1dg/
- deleted 3y ago
  [deleted]
- eqvinox 3y ago
  > 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-technology/LAN9374T-I-ZMX/16915551 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 ;)
- dezgeg 3y ago
  Ethernet is already used to transmit radio signal over fiber which requires extremely tight variation in latency (probably more strict than automotive).
numpad0 3y ago
Automotive Ethernet is not 8P8C...that's not how they do it at all
- Moto7451 3y ago
  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.
  - eqvinox 3y ago
    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…
amelius 3y ago
If you go to a higher voltage, you will typically use smaller wires.
hinkley 3y ago
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.
- _ea1k 3y ago
  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.
  - p_l 3y ago
    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.
    - _ea1k 3y ago
      Despite Tesla's boastings, large casting machines have existed before. Automotive use is the new part.
      - p_l 3y ago
        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.
      - panick21_ 3y ago
        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.
tzs 3y ago
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?
- satiric 3y ago
  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.
- myself248 3y ago
  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.
  - aidenn0 3y ago
    For very low current wires, I've seen non-metalic (nylon?) strands woven in with the copper for mechanical strength.
- dreamcompiler 3y ago
  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.
jrockway 3y ago
> 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.
- deleted 3y ago
  [deleted]
- dreamcompiler 3y ago
  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 https://youtube.com/watch?v=ky1Z2klPalw
  - hef19898 3y ago
    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...
    - panick21_ 3y ago
      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.
grepfru_it 3y ago
I actually run Poe in my car to power a mini pc in the trunk. I guess I’m ahead of the game :)

contingencies 3y ago

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

jnsaff2 3y ago
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.
- contingencies 3y ago
  Historically and increasingly, automotive grade electronics are a separate genre to general electronics for reasons of safety.
  - bgnn 3y ago
    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.
- bgnn 3y ago
  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/ 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.
rfdonnelly 3y ago
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 https://en.wikipedia.org/wiki/Time-Sensitive_Networking [2] https://1.ieee802.org/tsn/802-1dg/ https://1.ieee802.org/tsn/802-1dg/
deleted 3y ago
[deleted]
eqvinox 3y ago
> 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-technology/LAN9374T-I-ZMX/16915551 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 ;)
dezgeg 3y ago
Ethernet is already used to transmit radio signal over fiber which requires extremely tight variation in latency (probably more strict than automotive).

numpad0 3y ago

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

Moto7451 3y ago
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.
- eqvinox 3y ago
  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…

amelius 3y ago

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

hinkley 3y ago

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.

_ea1k 3y ago
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.
- p_l 3y ago
  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.
  - _ea1k 3y ago
    Despite Tesla's boastings, large casting machines have existed before. Automotive use is the new part.
    - p_l 3y ago
      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.
    - panick21_ 3y ago
      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.

tzs 3y ago

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?

satiric 3y ago
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.
myself248 3y ago
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.
- aidenn0 3y ago
  For very low current wires, I've seen non-metalic (nylon?) strands woven in with the copper for mechanical strength.
dreamcompiler 3y ago
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.

jrockway 3y ago

> 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.

deleted 3y ago
[deleted]
dreamcompiler 3y ago
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 https://youtube.com/watch?v=ky1Z2klPalw
- hef19898 3y ago
  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...
  - panick21_ 3y ago
    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.

grepfru_it 3y ago

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