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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

#151

Post by brandonagr2 »

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?

Doing it first is innovative

Re: Tesla shares 48V architecture with other automakers

#152

Post by Tempest1981 »

myself248 wrote: post #118
SigmundA wrote: post #55

Earlier quoted context omitted.

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.

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 bothe…

> 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.

Re: Tesla shares 48V architecture with other automakers

#153

Post by bgnn »

contingencies wrote: post #97
jnsaff2 wrote: post #87

Earlier quoted context omitted.

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.

Historically and increasingly, automotive grade electronics are a separate genre to general electronics for reasons of safety.

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.

Re: Tesla shares 48V architecture with other automakers

#154

Post by bloggie »

firebat45 wrote: post #27
mccoyc wrote: post #3

Earlier quoted context omitted.

Agreed. 48V (actually -48V) has been used across telco central offices for decades.

How exactly do you define a negative voltage unless you are using some other voltage as a reference?

Voltage is a measure of charge difference so there must always be a reference, usually the reference is 0 V.

Re: Tesla shares 48V architecture with other automakers

#155

Post by dududhxhd »

jmrm wrote: post #141

>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…

Nonsense. It’s a bit of self deprecating humor and gives readers enough information to follow along.

Re: Tesla shares 48V architecture with other automakers

#157

Post by myself248 »

cogman10 wrote: post #129
mcguire wrote: post #81

Earlier quoted context omitted.

The rumor I heard was that the higher voltage resulted in lower switch lifetimes. Any truth to that?

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 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.digikey.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.

Re: Tesla shares 48V architecture with other automakers

#158

Post by shermantanktop »

jauntywundrkind wrote: post #31
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.

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.

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.

Re: Tesla shares 48V architecture with other automakers

#160

Post by _ea1k »

etamponi wrote: post #159

If higher voltage leads to benefits, then why 48 and not 120 (US) or 230 (EU)? Or higher? What are the tradeoffs?

48V still counts as "low voltage" for safety purposes. The lower voltage gets them increased safety when working with exposed wiring.
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