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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) an

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 3y ago
https://de.wikipedia.org/wiki/Bordnetz#48-Volt-Bordnetz_im_Automobil 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 3y ago
  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 3y ago
    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 3y ago
      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 3y ago
      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 3y ago
        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.
SkyPuncher 3y ago
You can run smaller wires through the vehicle then down voltage on device.
CamperBob2 3y ago
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 3y ago
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-deal-for-copper-says-musk/ https://www.mining.com/new-tesla-low-voltage-system-a-big-de...
- bluGill 3y ago
  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 3y ago
  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 3y ago
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 3y ago
  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 3y ago
    It has been optimal to run accessories electrically for ICE already for several reasons. It has been difficult based on some of the loads on a 12v battery (agm has really helped this) - Start stop is smoother (and more available) without accessories - Cooling a turbo after the motor is off - true for the engine as well, heat soak on water pump off can go ~20f over the thermostat - Brake Boosting without a vacuum (Valvetronic or Hybrid) - Air Conditioning at idle
- lizknope 3y ago
  > Power steering pumps are electric and have one of the largest wires in my truck. Most new cars don't have hydraulic power steering systems anymore and use an electric motor for power steering. It improves fuel economy as well but the steering feel is generally worse than a hydraulic power steering system.
fasteddie31003 3y ago
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 3y ago
Here is an explainer: https://youtu.be/ky1Z2klPalw?t=573 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 3y ago
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&t=3679 https://www.youtube.com/live/Hl1zEzVUV7w?si=-Vz0gKT5YDbtrG9V... The sub section (~4min) on 48V in particular: https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7&t=4010 https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7...
londons_explore 3y ago
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.
- deleted 3y ago
  [deleted]
londons_explore 3y ago
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 3y ago
  if you're switching 48v, you'd want a mosfet rated for way more than 50v. On a car you'd want 200% headroom at least.
  - londons_explore 3y ago
    With totally uncontrolled bus capacitance and inductance, sure. But when you're using the same bus for Comms you need to have control of high frequency spikes, and low frequency spikes are easily handled by a bidirectional DC/DC. Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.
    - KaiserPro 3y ago
      > Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt. https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HDBK-217F.pdf https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HD... disagrees.
mauvehaus 3y ago
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 3y ago
  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 3y ago
    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 3y ago
      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 3y ago
        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 3y ago
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 3y ago
  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 3y ago
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_ 3y ago
  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 3y ago
> 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 3y ago
  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 3y ago
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_ 3y ago
waterheater 3y ago
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 https://en.wikipedia.org/wiki/American_wire_gauge
- contingencies 3y ago
  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--driving-technology-forward 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.
TaylorAlexander 3y ago
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%2FTwisted-Fields%2Frp2040-motor-controller%2Fblob%2Fmain%2FRP2040_motor.kicad_pcb https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2FTwis...
noncoml 3y ago
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?
codeulike 3y ago
As well as switching to 48V they are going to use Ethernet cables for most of it (PoE). So at the same time they get rid of the CAN bus wiring and have everything running on ethernet for communications and power, which means a LOT less wiring because with CAN bus every device needs its own wire but with Ethernet its much easier to have 'hubs' that channel communications and power on to other devices. https://twitter.com/cybrtrkguy/status/1731658374775771297?s=46 https://twitter.com/cybrtrkguy/status/1731658374775771297?s=...

pgeorgi 3y ago

https://de.wikipedia.org/wiki/Bordnetz#48-Volt-Bordnetz_im_Automobil 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 3y ago
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 3y ago
  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 3y ago
    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 3y ago
    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 3y ago
      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.

SkyPuncher 3y ago

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

CamperBob2 3y ago

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 3y ago

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-deal-for-copper-says-musk/ https://www.mining.com/new-tesla-low-voltage-system-a-big-de...

bluGill 3y ago
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 3y ago
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 3y ago

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 3y ago
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 3y ago
  It has been optimal to run accessories electrically for ICE already for several reasons. It has been difficult based on some of the loads on a 12v battery (agm has really helped this) - Start stop is smoother (and more available) without accessories - Cooling a turbo after the motor is off - true for the engine as well, heat soak on water pump off can go ~20f over the thermostat - Brake Boosting without a vacuum (Valvetronic or Hybrid) - Air Conditioning at idle
lizknope 3y ago
> Power steering pumps are electric and have one of the largest wires in my truck. Most new cars don't have hydraulic power steering systems anymore and use an electric motor for power steering. It improves fuel economy as well but the steering feel is generally worse than a hydraulic power steering system.

fasteddie31003 3y ago

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 3y ago

Here is an explainer: https://youtu.be/ky1Z2klPalw?t=573 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 3y ago

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&t=3679 https://www.youtube.com/live/Hl1zEzVUV7w?si=-Vz0gKT5YDbtrG9V... The sub section (~4min) on 48V in particular: https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7&t=4010 https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7...

londons_explore 3y ago

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.

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londons_explore 3y ago

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 3y ago
if you're switching 48v, you'd want a mosfet rated for way more than 50v. On a car you'd want 200% headroom at least.
- londons_explore 3y ago
  With totally uncontrolled bus capacitance and inductance, sure. But when you're using the same bus for Comms you need to have control of high frequency spikes, and low frequency spikes are easily handled by a bidirectional DC/DC. Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt.
  - KaiserPro 3y ago
    > Therefore I could imagine peak to peak ripple on this bus to never exceed 1 volt. https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HDBK-217F.pdf https://www.quanterion.com/wp-content/uploads/2014/09/MIL-HD... disagrees.

mauvehaus 3y ago

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 3y ago
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 3y ago
  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 3y ago
    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 3y ago
      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 3y ago

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 3y ago
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 3y ago

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_ 3y ago
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 3y ago

> 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 3y ago
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 3y ago

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_ 3y ago

waterheater 3y ago

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 https://en.wikipedia.org/wiki/American_wire_gauge

contingencies 3y ago
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--driving-technology-forward 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.

TaylorAlexander 3y ago

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%2FTwisted-Fields%2Frp2040-motor-controller%2Fblob%2Fmain%2FRP2040_motor.kicad_pcb https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2FTwis...

noncoml 3y ago

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?

codeulike 3y ago

As well as switching to 48V they are going to use Ethernet cables for most of it (PoE). So at the same time they get rid of the CAN bus wiring and have everything running on ethernet for communications and power, which means a LOT less wiring because with CAN bus every device needs its own wire but with Ethernet its much easier to have 'hubs' that channel communications and power on to other devices. https://twitter.com/cybrtrkguy/status/1731658374775771297?s=46 https://twitter.com/cybrtrkguy/status/1731658374775771297?s=...