[HN Gopher] Tesla shares 48V architecture with other automakers
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Tesla shares 48V architecture with other automakers
Author : toomuchtodo
Score : 112 points
Date : 2023-12-07 15:10 UTC (7 hours ago)
(HTM) web link (electrek.co)
(TXT) w3m dump (electrek.co)
| sitkack wrote:
| TIL that 42V fizzled out
| https://en.wikipedia.org/wiki/42-volt_electrical_system
|
| I welcome the move to 48V, as one gets lots of cross over
| synergies from the 48V telco standard.
|
| https://www.servertech.com/blog/48vdc-power-and-the-backbone...
|
| https://www.st.com/content/dam/AME/2019/developers-conferenc...
|
| https://www.maximintegrated.com/content/dam/files/products/p...
|
| https://www.infineon.com/cms/en/applications/information-com...
| mccoyc wrote:
| Agreed. 48V (actually -48V) has been used across telco central
| offices for decades.
| kurthr wrote:
| It's a really nice voltage with lots of support for batteries
| and up/dn conversion hardware.
|
| It's also right at the edge of what is human safe. You can
| burn yourself and blow up cables, but it's very difficult to
| electrocute yourself (afib or muscle seize) without lots of
| wet contact.
|
| https://incompliancemag.com/article/experiments-of-dc-
| human-...
| jacquesm wrote:
| Indeed, I'm aware of only one recorded death by
| electrocution at 48V, iirc it was a Swiss radio amateur
| that had done a bunch of gardening sat down sweaty in a
| metallic chair and reached for the one switch of his set.
| Probably there were other contributory causes as well, I've
| been zapped multiple times from much higher voltage sources
| (that could have easily supplied the power required) and
| lived.
|
| I can't find a reference for that Swiss case though. I'll
| keep looking.
| firebat45 wrote:
| How exactly do you define a negative voltage unless you are
| using some other voltage as a reference?
| dragontamer wrote:
| Label the power pin+ GND and the power pin- becomes -48V
|
| Voltages are all relative. It's like saying 'How do you get
| a height difference of 10 feet by digging?'
|
| Well, you dig and then label the initial level as +10 feet,
| and redefine the bottom of your hole to be ground.
| Kirby64 wrote:
| No. In telco, the -48V is referenced against ground, like
| the physical ground. If you're isolated, you can do this.
| but they would still need to be referencing the 'ground'
| to something ... likely the negative side of the main
| battery pack.
|
| The reason why -48V is used is because it is provided as
| a bias voltage to give wiring cathodic protection, to
| prevent corrosion of telecom infrastructure. If you used
| 48V, it would not work. You need a negative voltage
| referenced against ground.
| applied_heat wrote:
| Ground positive terminal of battery string instead of
| grounding negative terminal.
|
| I see this more often on European stuff
| bluGill wrote:
| Generally with respect to ground. There are many good
| reasons to connect your power system to ground and so this
| is commonly done. (there are pros and cons to connecting to
| ground, but it gets complex fast)
| myself248 wrote:
| It is with respect to ground, the positive pole of the
| battery is connected to ground.
|
| The telegraph system figured this out very quickly. Most
| water in nature has at least a bit of salt in it, which is
| present as positive sodium ions and negative chloride ions.
| By making the outdoor wiring negative with respect to
| ground, the chloride ions are repelled, and such wires
| corrode much more slowly than those that're positive with
| respect to ground.
|
| Since most of the telegraph network, later the telephone
| network, is outdoors, this is a pretty big deal.
| thebruce87m wrote:
| > that're
|
| First time I've ever seen this typed
| hinkley wrote:
| What're you talking about?
| denysvitali wrote:
| I guess he refers to the shortening of "that are" into
| that're
| magicalhippo wrote:
| It's a matter of perspective.
|
| You tie one of the leads to earth (literally grounding
| it)[1], leaving the other non-grounded. Depending on if you
| tie the negative or the positive lead to ground, you get
| 48V or -48V with respect to ground. As long as the
| potential between the most positive lead and the least
| positive lead is 48V, the circuit itself doesn't care.
|
| As mentioned here[2], the reason for grounding the positive
| lead is to prevent galvanic corrosion[3] destroying the
| buried copper.
|
| [1]: https://www.bicsi.org/docs/default-source/conference-
| present...
|
| [2]: https://www.poweringthenetwork.com/uncategorized/negat
| ive-48...
|
| [3]: https://en.wikipedia.org/wiki/Galvanic_corrosion
| hinkley wrote:
| Apparently in cars it's weirder. Wire it one way and the
| wiring corrodes. Go the other way and the body corrodes.
| bloggie wrote:
| Voltage is a measure of charge difference so there must
| always be a reference, usually the reference is 0 V.
| londons_explore wrote:
| I don't think they'll be able to use much of that with their
| 48v PoE ethernet standard...
| SigmundA wrote:
| As mentioned in the 42v article they went with that due to 48v
| nominal being too close to 60v max on alternator/fully charged
| which is the limit shock hazard.
|
| Not sure what chemistry/cell count will be for the 48v battery
| (which I assume it has) but 48v could mean 13s - 16s packs.
| pupppet wrote:
| Do more stuff like this, Elon. I really don't like not liking
| you.
| r3d0c wrote:
| weird comment... maybe we shouldn't feel the need to idolize
| humans...
| flappyeagle wrote:
| It's ok to like people
| rnk wrote:
| We humans are all terrible on some level (except my mom, she
| was a saint), but if you have enormous power, you can help or
| hurt a lot of people based on your actions. Musk has a lot of
| power. He must be a terribly lonely person, not knowing if he
| can trust anyone or they just want something from him.
| firebat45 wrote:
| Nobody knows if they can trust anyone, not just rich
| people.
| argiopetech wrote:
| Right, but it's a lot easier when you don't have anything
| someone else might want, much less a billion or more
| things.
| davidcbc wrote:
| He could give away 99.99% of his wealth, still never have
| to work another day in his life, and be much less of a
| target if he wanted to. Boo hoo the poor guy who has more
| money than almost anyone has ever had in the history of
| the earth has problems
| bluGill wrote:
| True, but it isn't worth a thief's time to steal things
| from me, so I'm less a target of dishonest people. Not
| zero target, but not a big target. Rich people because
| they have money are a larger target. Nobody would seek to
| marry me for my money - filing for divorce as soon as
| enough time has past to make it look like that wasn't
| their goal - a small number of people would do that and
| they seek out rich people.
| SilverBirch wrote:
| Hi, excuse me. Just want to say, don't appreciate you
| rounding me up with the anti-semites. "We humans". No -
| those anti-semites, and us reasonable people. Wouldn't like
| to mix with them thanks. You can make whatever excuses you
| want for him, but that's what they are, excuses.
| itishappy wrote:
| Is "he's not doing enough cool stuff" really the root of your
| dislike of Elon?
| jandrese wrote:
| Don't worry, it will only be a matter of time before he
| retweets a neo-Nazi and you can go back to hating him.
|
| Some people have way too binary a view of other people. In real
| life there are rarely outright villains or complete saints.
| Everybody is a mix of greys. You don't have to agree with
| _everything_ a person does or says to appreciate their work.
| pupppet wrote:
| Retweeting neo-nazi content is no shade of grey.
| intrepidhero wrote:
| 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.
| pgeorgi wrote:
| 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 wrote:
| 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 wrote:
| 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.
| bluGill wrote:
| 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.
| taylodl wrote:
| 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 wrote:
| 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.
| pgeorgi wrote:
| 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.
| bryanlarsen wrote:
| It'd be cheaper to delete the 12V bus entirely and add
| 48V -> 12V converters in front of legacy components, even
| if they needed several dozen of those converters.
| panick21_ wrote:
| I expect Tesla to still have a few components like that
| in the car.
| jabl wrote:
| > 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.
| atoav wrote:
| In sotuations where it is about space you wouldn't choose
| aluminum. Also afaik most automotive wiring that is
| certified is copper. Going from copper to aluminum means
| you will have to put bigger crossections in. This is more
| weight and more space.
| taylodl wrote:
| 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.
| jandrese wrote:
| Total current consumption should be about the same (or
| even less, thanks to lower losses at 48v), so I'm not
| sure why would you would need a "much beefier"
| alternator. It will need different windings, but overall
| it should be about the same size and cost.
| Kirby64 wrote:
| 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.
| smileysteve wrote:
| What modern phone charges at 12v?
|
| Most phones charge at 5v. Modern USB-C chargers can
| charge between 5v and 20v based on configuration.
|
| Buck converts and regulators are cheap and small these
| days.
| nikau wrote:
| Most phones charge higher than 5 volts these days
| SkyPuncher wrote:
| You can run smaller wires through the vehicle then down voltage
| on device.
| CamperBob2 wrote:
| _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.
| rnk wrote:
| 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...
| bluGill wrote:
| 6 volt autos were going out of style in the 1950s. They did
| last into the 1960s, but they were already rare by then.
| bokohut wrote:
| 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!
| jabart wrote:
| 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 wrote:
| 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 wrote:
| 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
| fasteddie31003 wrote:
| 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.
| adolph wrote:
| 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._
| martythemaniak wrote:
| 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...
| londons_explore wrote:
| 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.
| londons_explore wrote:
| 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 wrote:
| 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.
| mauvehaus wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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?!
| bryanlarsen wrote:
| 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 wrote:
| 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)
| PinguTS wrote:
| 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_ wrote:
| 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.
| tshaddox wrote:
| > 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 wrote:
| 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.
| myself248 wrote:
| 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.
| panick21_ wrote:
| Awesome to hear from an expert. Im looking forward to some
| teardowns to see how the set this all up.
| mcguire wrote:
| The rumor I heard was that the higher voltage resulted in
| lower switch lifetimes. Any truth to that?
| cogman10 wrote:
| 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 wrote:
| 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.di
| gikey.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.
| tootie wrote:
| 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 wrote:
| > 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.
| myself248 wrote:
| 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.
| brandonagr2 wrote:
| Doing it first is innovative
| carabiner wrote:
| 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?
| Tuna-Fish wrote:
| 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.
| brandonagr2 wrote:
| 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
| waterheater wrote:
| 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 wrote:
| _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 wrote:
| 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 wrote:
| 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
| TaylorAlexander wrote:
| 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...
| noncoml wrote:
| 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?
| adolph wrote:
| It is interesting to think about how an automaker like Tesla
| which is more vertically integrated and has less in the way of
| legacy parts/tools/processes can make this change more easily
| than the established players. From the article:
|
| _If you cannot convert all of a vehicle's systems to 48V
| architecture, the benefits of using such an architecture start to
| diminish pretty quickly . . . If an automaker decides to move to
| a 48V architecture, whatever car it builds must use 48V-ready
| accessories. But, suppliers aren't incentivized to build such
| accessories without sufficient demand._
| elp wrote:
| 48Vdc is supposedly the highest voltage that is still considered
| safe.
| (https://electronics.stackexchange.com/questions/267789/how-s...)
|
| It certainly sounds like a smart move on the copper savings
| alone.
| jauntywundrkind wrote:
| Extra low voltage is 50v ac or 100v dv.
| https://en.wikipedia.org/wiki/Extra-low_voltage
|
| For some reason people assume it's 48v DC or 50v dc. But it's
| double that. That said, I feel significantly more scared
| dealing with 100v DC than I do 48 or 24v.
| myself248 wrote:
| That's for IEC. Under OSHA it's 50 volts, AC or DC.
| sheepshear wrote:
| ELV is not a fundamental definition of "safe". The limits of
| what's safe depends on the application and your risk
| tolerance, and ELV is just a name for a couple of definitions
| out of many.
|
| Also, those numbers are for ripple-free DC, which you're not
| going to find in a car. They're cut roughly in half for
| ripple peaks.
| amluto wrote:
| I find 48V a lot less scary when cars are involved than 12V.
| Neither is particularly likely to electrocute me, but 48V
| comes with fuses that will trip at 1/4 the current, giving
| 1/16 the resistive heating if something shorts, which is a
| lot less likely to melt or ignite things. Also, the wires are
| much smaller :)
| thot_experiment wrote:
| > 1/4 the current, 1/16 the resistive heating
|
| Really underappreciated safety aspect. The currents
| required for your average doodad at 48V leave you with a
| MUCH lower chance of unscheduled welding.
|
| Remember folks, everything is a fuse if you put enough
| current through it, as a rule of thumb it's good to keep
| "enough" pretty low.
| shermantanktop wrote:
| I used to work on vacuum tube power amps. 400v+ B+ with big
| caps is stressful to deal with. And doing it a lot can lead
| to complacency.
|
| We used to call getting shocked "getting a taste" - like
| getting a taste of ice cream, except it's more like a
| microsecond blackout.
| SigmundA wrote:
| Remember a fully charged lithium battery with nominal 48v can
| be close to 60v just like 12v in your car is actually closer to
| 14v.
| wongarsu wrote:
| However there is a lot of leeway on the "48V is the highest
| safe voltage" statement too. 48V has a special place in
| regulations because of its use in telco, but 60V DC is still
| very safe.
| hinkley wrote:
| Doubling again to 96 is not safe, however. I'm not sure why
| they settled on powers of two. Something perhaps to do with
| noise filtration, and fewer new tricks to learn?
| myself248 wrote:
| It's convenient to build things in multiples and powers
| of 2 and 3. A nice two-tier or four-tier battery rack
| full of 2-volt cells just works out nicely.
| hinkley wrote:
| Smaller transformers with whole numbers, right? But why 4
| and not 3 or 6?
| TaylorAlexander wrote:
| Sure but they can feed the system through a regulator if
| they'd like. Do we have any reason to believe they are
| tapping directly on to a pack for this part of the system?
| myself248 wrote:
| For battery-powered systems the nominal voltage is used.
| Telephone "48 volts" is 55.2 volts in practice, only falling
| near 48 if there's a power failure and the office generators
| don't autostart in a timely fashion.
|
| That's never caused any regulatory problems for Ma Bell,
| despite OSHA saying 50v is the cutoff. And personally having
| spent roughly a decade of my career crawling all over such
| systems, 55.2 doesn't bother me one bit.
|
| Span-powered T1 at 130VDC, on the other hand.... that'll poke
| ya. That gets little plastic covers over all the terminals,
| but they have been known to fall off. So there is a
| meaningful threshold, and 55.2 is solidly below it.
|
| Which suggests to me that there's a good bit of leeway built
| into the standards, perhaps specifically so they don't have
| to wheedle about whether a battery system should be measured
| at its nominal voltage, its float voltage, its absorption
| voltage, its peak/equalization voltage, its....
| Tempest1981 wrote:
| > That's never caused any regulatory problems for Ma Bell,
| despite OSHA saying 50v is the cutoff
|
| I seem to recall getting a buzz when touching phone wires -
| while the line was ringing. I think I measured around 100
| VAC. Apparently that's "ok", safety-wise.
| rational_indian wrote:
| Could have gone higher. Worth it in copper savings alone. IIRC
| the cars use AC motors. It needs to go through inverters anyway
| so there is some flexibility in how high you can go.
|
| Edit: of course the motors are "AC" who would want a brush and
| commutator based motor in their car?
| bryanlarsen wrote:
| Most countries have safety rules that apply at 50V, so staying
| below that reduces regulatory costs significantly.
| rational_indian wrote:
| Good point.
| epx wrote:
| It would be great to have 48VDC in homes, for lightning, light
| appliances, etc. to centralize the whole power factor control in
| a single big power supply instead of doing it (poorly, or not at
| all) at every LED bulb.
| bryanlarsen wrote:
| It'll happen in RV's first, for obvious reasons. I imagine
| they'll use USB-C as the standard connector even though it's
| not the optimal form factor for this usage due to its ubiquity.
| POE would be a better choice.
| tootie wrote:
| Doesn't USB-C cap at 20V?
| ianburrell wrote:
| Latest USB-PD standard allows for 48V and 240W. It uses
| special EPR marked cables.
| candiddevmike wrote:
| Replace all power outlets with Ethernet and have everything run
| over 48V PoE and get network connectivity too
| bokohut wrote:
| While this sounds great in practice the reality will be far
| from ideal for the singular reason of security. The cyber
| issues are compounding at exponential rates as more and more
| devices that make things "easy" lack even the most basic
| security protocols and the production targets to generate
| revenue asap have zero to nil concern around protecting said
| devices from nefarious actors while in use. When the
| electrical and data transfer grid become one, as I believe it
| must for reasons of efficiency, we are certain to witness
| chaos and losses like never before. What you cannot see
| matters most! and in time many will pay the ultimate cost for
| someone else's 'easy'.
| vlovich123 wrote:
| More like basically every electronics product uses AC. It's
| a two sided market problem - there's no demand because
| there's no supply and no supply because there's no demand.
|
| The security aspects are solvable through various standards
| (eg we have LAN over power lines and coax already and they
| layer encryption on top to build the mesh while balancing
| UX). The security concerns may be the #1 concern for you
| but has nothing to do with market adoption.
| ianburrell wrote:
| PoE 802.3bt tops out at 71W. Not even enough to enough to run
| big USB-C adapter. Also, PoE is pretty lossy which defeats
| the whole purporse of using DC to save energy.
| bluGill wrote:
| You would need larger wires to account for the losses at a
| house scale. Since nothing runs are 48 volts you still have the
| bad power supply in every LED bulb.
| jnsaff2 wrote:
| The Dutch have some homes that are DC. Here's even a paper
| discussing this[0]. There is also a presentation that mentions
| DC homes from page 18[1].
|
| [0] - https://www.irbnet.de/daten/iconda/CIB2595.pdf [1] -
| https://fhi.nl/app/uploads/sites/38/2018/06/10.00-DC-Power-e...
| ianburrell wrote:
| The DC power for LED varies based on the bulb and most are less
| than 48V. Which means you end up with DC-DC converter in each
| one. DC-DC is slightly more efficient than DC-AC but not enough
| to make worth converting.
|
| The same is true of electronics, you are replacing AC-DC
| charger with DC-DC charger.
|
| The other big problem is that lots of appliances require more
| power than feasible with 48V. People are fine with the low-
| power DC right up until they need to plug in a space heater.
| Are you going to have two kinds of outlets everywhere? Or
| incrementally upgrade each circuit? Or are going to upgrade the
| wiring with super thick cable that can handle the current?
| londons_explore wrote:
| Am I right in saying this _wasn 't_ shared with the public or
| other (Chinese) OEM's...
|
| Doesn't that raise collusion/anti competitive concerns? Or is
| Elon relying on the fact no prosecutor will take a case about
| disadvantaging china?
| KaiserPro wrote:
| "shared" in the sense that everyone else was doing it already.
| In the same way that he's shared the hyperloop, which he got
| from a 1980s osbourne book of transport.
| panick21_ wrote:
| I think the more important change that Tesla made is the change
| in the databus. Much higher performance ethernet. They changed
| the whole architecture of the car where there are now very few
| point to point connection, and its all essentially routed with a
| few major modules in each part of the car.
|
| If you look at current cars there are sometimes huge cable
| bundles, lots of individual cables for everything. Its a
| nightmare to build up and very hard to install.
|
| I think in their next generation assembly they will have these
| connection points be fixed and then just plug different sub
| assembly together at predetermined points. No more huge cable
| harness installed on completed bodies.
| KaiserPro wrote:
| > Much higher performance ethernet.
|
| Depends what performance you are after. Ethernet isn't rated
| for safety critical stuff. It doesn't provide mechanisms for
| packet loss detection, and in most cases is pretty shit at flow
| control.
|
| Ethernet is also shit for small sensors/actuators. There are
| lots of low bandwidth devices that need power and comms,
| ethernet isn't designed for that. having to route 2 pairs of
| cables to everything in a star pattern is really impractical.
|
| Its probably ok for linking different zones, of non critical
| stuff. But running PoE? for all but specialist things, that
| sounds frankly stupid.
| 7e wrote:
| Mild hybrids have been using 48V for a long time. There isn't
| much new here except that Tesla decided to do every component.
| That's going to cause quality problems with parts if they remain
| a tech. island in the industry, so trying to get everyone else on
| board makes sense.
| panick21_ wrote:
| Doing it for everything is the whole point, it changes the
| architecture of the car. Yes individual components but those
| cars had like 1% if connected devices at that voltage and were
| otherwise exactly the same.
|
| For Tesla ist a replacment of something else, for previous
| vehicle was it was something additional for a specialized use
| case.
| yinser wrote:
| 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 also means reduced heat produced
| TheLoafOfBread wrote:
| > 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.
| KaiserPro wrote:
| > 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
|
| Ethernet isn't a bus, its point to point. PoE over cat5/6 uses
| 4 pairs of UTP.
|
| so it might be used to join aggregate things together, but it
| won't be a bus.
|
| Yes, you can increase the datarate, but ethernet is
| fundamentally unreliable. So you'll need to either strictly
| manage the bandwidth requirements of attached devices, or put
| in flow control(expensive) or use the weird "reliable" Ethernet
| they made for fibre channel replacment ($lol and you need to
| pay to make it automotive rated)
|
| 48v is logical, and a lot of other people are doing it.
|
| PoE is probably stupid
|
| Ethernet makes kinda sense, but firewire would probably be
| better, its a bus and rated for life critical use.
| TheLoafOfBread wrote:
| Ethernet can be used as a bus (see CSMA/CD), but if there are
| more than 2 nodes, performance of whole bus will go to
| complete shit and there is no guarantee that an ECU will
| transmit a single packet during its run, because that CD has
| no automatic arbitration, it is just random disconnection and
| try again. Not good for critical things like ABS. That's also
| whole reason why FlexRay was spawned, because even that FR is
| inflexible abomination of a protocol it actually guarantees
| that every ECU on the network will get a time window to
| transmit its own data.
| KaiserPro wrote:
| > CSMA/CD
|
| Lol I'd forgotten about base-T.
| pedrocr wrote:
| Golf carts have used mainly 48V for traction for a long time. And
| there are now great options for 48V LFP batteries for them. So
| far that usually means also running a 12V converter to power
| accessories. If the automotive world finally gets their act
| together on 48V this will be great for all kinds of DIY uses. The
| batteries and chargers are already here. There are a bunch of off
| grid and mobility applications that should be made simpler by
| this. Hopefully the automotive supply chain moves meaningfully
| around this.
| MisterTea wrote:
| I've been waiting for higher automotive voltage for a long time.
| Way back I wished for 48V as it's double the 24V standard used in
| European and off highway trucks as well as industrial automation
| and -48V is used in telecom. Wires can now carry 4x power. But
| from memory there was a 50V safe limit that would complicate
| things as the 48V charging voltage exceeds 50V as does the
| nominal cell voltage. So instead the industry selected 36V and
| planned to migrate but it never happened. The reason being LED
| lighting and small more efficient electronics reduced the need
| for higher voltages.
|
| With EV's there's no reason to keep 12 V.
| jnsaff2 wrote:
| 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 wrote:
| 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)
| jnsaff2 wrote:
| 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 wrote:
| Historically and increasingly, automotive grade electronics
| are a separate genre to general electronics for reasons of
| safety.
| bgnn wrote:
| 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 wrote:
| 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.
| rfdonnelly wrote:
| 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/
| numpad0 wrote:
| Automotive Ethernet is not 8P8C...that's not how they do it at
| all
| amelius wrote:
| If you go to a higher voltage, you will typically use smaller
| wires.
| hinkley wrote:
| 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.
| tzs wrote:
| 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 wrote:
| 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.
| simplypeter wrote:
| The thing is, unless the whole industry moves together to 48V,
| the cost of this change for a single OEM+Tier1 would be too big.
| MetaWhirledPeas wrote:
| In cases where they're using a proprietary 48v part I wonder if
| Tesla would consider becoming a parts supplier to other
| manufacturers?
| SilverBirch wrote:
| This is basically the crux of the matter. Traditional
| automakers are a complex supply chain that standardises and
| goes to extra-ordinary lengths to reduce costs. Tesla build a
| tonne of their own stuff and aren't as price sensitive. The
| question is "Why don't we just redesign all this stuff" and the
| answer is "We're Ford, we make tiny margins and we can't afford
| to redesign our entire car every year and even if we could we
| get half our components from Bosch anyway". Not to mention the
| difficulty in convincing FuSa people your arbitrary ethernet
| network is safe.
| jmrm wrote:
| >48V architecture also potentially improves overall electrical
| efficiency for reasons that I am not sufficiently qualified to
| explain beyond a kindergarten level
|
| This is double bad in a green energy and EV website: On one hand,
| they admit they don't now why that happens, but on the other
| hand, they also didn't research just a bit more on that, and
| that's bad journalism.
|
| Most of the comment threads in this HN post are a lot more
| informative than the article
| CamperBob2 wrote:
| Also, "But don't you dare threaten to replace me with an LLM.
| Journalism is a sacred cornerstone of democracy and
| intellectual life!"
| wnevets wrote:
| I don't know if I would call a self proclaimed content
| marketer a Journalist.
| dududhxhd wrote:
| Nonsense. It's a bit of self deprecating humor and gives
| readers enough information to follow along.
| Animats wrote:
| Older Tesla cars have a 12V battery for accessories, until the
| main high-voltage battery is turned on. So does this mean having
| a 48V accessory battery? Or what?
| bloggie wrote:
| I don't know much about the Cybertruck, but in general all
| modern cars, electrically propulsed or not, have a 12 V system
| which includes a battery for running electronics and some
| accessories. Very old cars had a 6 V system. There is a push to
| move to higher voltages, the battery would also be 48 V to
| match. https://my.avnet.com/abacus/resources/article/the-shift-
| to-4...
| etamponi wrote:
| If higher voltage leads to benefits, then why 48 and not 120 (US)
| or 230 (EU)? Or higher? What are the tradeoffs?
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