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Tesla shares 48V architecture with other automakers

electrek.co

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Re: Tesla shares 48V architecture with other automakers

#261

Post by dgfitz »

bigdict wrote: post #256
mmaunder wrote: post #246

Many comments here seem to be confusing the accessories circuit voltage with the electrical vehicle motor and drive system. The vehicle motors have a combined power output of 450KW which requires a high voltage 800V system or the wiring would be so heavy it would not be feasible. This spec appears to be the accessories circuit with Tesla pushing for a new 48V standard. That’s super smart because it immediately means…

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

Higher the voltage the lower the amp draw, so smaller wires can be used.

Re: Tesla shares 48V architecture with other automakers

#262

Post by pertymcpert »

bigdict wrote: post #256
mmaunder wrote: post #246

Many comments here seem to be confusing the accessories circuit voltage with the electrical vehicle motor and drive system. The vehicle motors have a combined power output of 450KW which requires a high voltage 800V system or the wiring would be so heavy it would not be feasible. This spec appears to be the accessories circuit with Tesla pushing for a new 48V standard. That’s super smart because it immediately means…

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

For your first question, power = voltage x current. To transmit the same power, if you double the voltage you only need half the current. This is important because the resistance losses in conductors are related to the current not voltage, so you can use thinner wires without overheating.

Re: Tesla shares 48V architecture with other automakers

#263

Post by maxerickson »

bigdict wrote: post #256
mmaunder wrote: post #246

Many comments here seem to be confusing the accessories circuit voltage with the electrical vehicle motor and drive system. The vehicle motors have a combined power output of 450KW which requires a high voltage 800V system or the wiring would be so heavy it would not be feasible. This spec appears to be the accessories circuit with Tesla pushing for a new 48V standard. That’s super smart because it immediately means…

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

60 volts DC is a safety threshold. You start to move current through tissue at higher voltages.

Re: Tesla shares 48V architecture with other automakers

#264

Post by Turskarama »

dreamcompiler wrote: post #229
Turskarama wrote: post #221

Earlier quoted context omitted.

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

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

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

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

Re: Tesla shares 48V architecture with other automakers

#265

Post by dreamcompiler »

elihu wrote: post #210
Tuna-Fish wrote: post #108

Earlier quoted context omitted.

And to explain why this hadn't been done before/how we got here: Nothing in a car actually wants 12V DC. Most of the low voltage stuff will run better at 5V or below, while a lot of the higher voltage stuff would benefit from going as high as possible. 12V exists because DC-DC conversion used to be expensive, and you had to make a compromise about the voltage based on losses, wire thickness, and picking a low enough…

I think another big part of it is that DC switches tend to get expensive above 12V. Cheap AC switches work fine at higher voltage, because the arc is self-extinguishing as it passes through zero twice per cycle, but DC doesn't do that so you can end up with an arc that doesn't extinguish itself, which, aside from not turning the thing off when you want to, burns out the electrical contacts.

Now we have MOSFETS and IGBTs that can switch DC without sparks. I suspect most DC switching in the Cybertruck is relayed through these. (Except the main contactor and pyro fuse of course.)

Re: Tesla shares 48V architecture with other automakers

#266

Post by Kirby64 »

myself248 wrote: post #157
cogman10 wrote: post #129

Earlier quoted context omitted.

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 admitte…

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 f…

You're correct in all of that in regards to mechanical relays, but none of this matters for solid state devices. I'm not aware of any actual mechanical relays in Tesla's. They do have contactors for the HVDC connections, but that's about as close as you get to relays. Hell, they don't even have fuses; they use self reset-able 'soft' fuses.

You have to worry about shutting down current quickly (i.e., inductor flyback), but that's a pretty trivial problem to solve.

Re: Tesla shares 48V architecture with other automakers

#267

Post by dreamcompiler »

tootie wrote: post #85
myself248 wrote: post #60

Earlier quoted context omitted.

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 term…

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?

Musk said the 48v stuff was not innovative at all; they were only doing the latter things you pointed out.

Re: Tesla shares 48V architecture with other automakers

#268

Post by dreamcompiler »

Kirby64 wrote: post #258
dreamcompiler wrote: post #235

Earlier quoted context omitted.

Tesla uses 800v only to run the Cybertruck's drive motors. Every other electric load in the truck uses 48v. Both of these are much higher in the Cybertruck than all other Tesla models. All other Tesla models use 400v [IIRC] for the drive motors and 12v for everything else.

Pretty sure the AC/heat pump on the Cybertruck runs off the 800V pack. Since it consumes so much power for long periods of time, it makes little sense to run it off the 48V. Existing other Tesla's use the main pack voltage for AC/heat pump.

Good point and makes sense.

Re: Tesla shares 48V architecture with other automakers

#269

Post by phire »

sbierwagen wrote: post #238
Moto7451 wrote: post #189

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

>and the jumper pins It can be started through the converter? That takes something like a hundred amps. It must be pretty beefy.

No.

For safety, hybrids and electric vehicles physically disconnect the high-voltage battery from everything when it's off with massive relays. So you can end up in the somewhat stupid situation where your high-voltage battery is fully charged, but you can't do anything because the tiny 12v motorcycle battery is flat.

Starting simply requires enough 12v current to close a relay, the amps going though the "jumper pins" are tiny. And once the relay is closed, the high-voltage battery can keep the relay closed and charge the 12v battery via the dc-dc converter.

The amount of current to "jump" a hybrid or electric car is so small that they really should just install a USB-C cable, so you could just use your phone to jump start it.

Re: Tesla shares 48V architecture with other automakers

#270

Post by NotYourLawyer »

elp wrote: post #11

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.

With wet hands, even 48v hurts.
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