[jinzo]

I'm sure it depends on market, but I also know 100% that if they will certify the battery as safe, and then you get electrocuted when entering your car because the battery was not safe - they will be on the hook, in all developed markets. No one else, that cares about people safety, do the same thing for under $100. Even Tesla, that almost completely disregards any safety - be it "Full Self Driving" or "let's just change this, without checking if the battery is actually safe", does not do it under $100.

[Glawen]

Do you realise how difficult it is to get "electrocuted" in a battery powered vehicle ? I suggest you document yourself on the matter.

The only real issue in reality is thermal runaway

[amelius]

Yeah, what is the max voltage of these batteries?

[jacquesm]

Depends on the brand and the model, there is a trend towards higher voltages because that implies lower currents and wiring is heavy and expensive.

It started out with (nominally, voltage can rise and fall based on charge levels) (30S) 144V packs, (96S) 352V is very common and there are (192S) packs that do 704V (but that are marketed as 400V and 800V respectively).

You don't want to get zapped by any of these, it's middle voltage DC which is quite dangerous, so the fuses definitely have a safety aspect in case of a crash, they are to protect emergency personnel from touching the frame and exposed wiring. But that's in case of a very serious crash, your average encounter with a rabbit might set off the crash detector (which can't really know ahead of time how bad a crash will be) but has extremely little chance of resulting in exposed wiring. In the case of BMW that rabbit could end up being pretty expensive.

[amelius]

Yikes, that sounds dangerous.

I'd personally prefer e.g. 48V even if that meant some more losses and/or thicker cables.

[jacquesm]

> Yikes, that sounds dangerous.

It is.

> I'd personally prefer e.g. 48V even if that meant some more losses and/or thicker cables.

That's unfortunately not an option. The problem with the 600 to 1000 V domain is that it is able to creep where lower voltage would stay constrained and high enough that it can jump small gaps and start arcing spontaneously. The fact that it is DC makes it more dangerous still. But from an economy and practical engineering perspective it makes perfect sense. Keep in mind that these cars are often built using Lithium-Ion packs (though fortunately we are finally seeing a change here towards safer options, even if they are slightly less dense and more expensive), so the electrocution risks are small compared to the thermal runaway risks.

[Kirby64]

Running an EV off 48V would lead to a heavily, heavily compromised vehicle. There just aren’t components that can handle 5-10kA of current with a reasonable size.

[amelius]

What parts of the car need that amount of current?

Are you talking about the charging circuitry?

What are the requirements for the motor(s)?

[quickthrowman]

It’d be a massive waste of electrical conductors to use 48V batteries due to ampacity. Higher voltage means lower ampacity and smaller conductors.

You’d need to use silver plated copper buss bar as conductors, 150kW @ 48VDC is 3125 Amps. I’m not familiar with DC ampacity tables, but you’d need (9) 3” conduits each containing (3) #500 MCM conductors for a three-phase 3125A alternating current circuit. One foot of #500MCM copper weighs 1.5 lbs, so each foot would have 27 times 1.5 lbs or 40.5 lbs per foot.

150kW @ 400V is 375A, a single set of #500MCM can carry the current, 4.5 lbs per foot.

The risk of being shocked by 400VDC while using the car is essentially 0, so they use higher voltage to save on conductor material.

There’s no way in hell I’d ever open up an EV battery myself and I know enough to do it safely. DC is incredibly scary, make sure to discharge your start/run caps if you replace them yourself!

[jacquesm]

And if you do ever open up a car battery pack the first order of battle is to split it in half.

[jinzo]

What are you talking about? Yes I know how quickly I can get electrocuted when the battery pack is open. I just need to touch two exposed busbars ~30cm apart. Or my tool needs to touch them.

[Glawen]

Exactly, you need to touch both plus and minus. You moved the goalpost from getting electrocuted driving your car due to shoddy quality remanufacturing of battery, to getting electrocuted while repairing the high voltage side of your vehicle. Remanufacturing quality does not come into play if you decide to touch plus and minus side of a HV battery.

[jinzo]

Sorry I have no idea about this goalpost moving, maybe it's a language barrier. I'm just saying working on it is quite dangerous. But you can easily get electrocuted by shoddy remanufacturing (especially if someone drilled into the battery to replace a single cell - as EV Clinic shows in their videos), that's why there are additional safeties with regards to bad isolation. So I stand by both takes.

[Tostino]

I disagree with your other takes in this thread, but you are 100% right here. This is dangerous stuff that needs to be treated with respect.

I don't think it should be locked away to just the MFG, but it does need to be respected.

[ricardobeat]

They mention in the article that replacing the same fuse on a Tesla cost €11.

[jacquesm]

Given that I've tried to hold BMW to their warranty and was shafted I would not bet on that.

[semanticist]

There's a difference between BMW ignoring their warranty and who gets found liable during the wrongful death lawsuit after the mechanic gets electrocuted due to poor/unsafe EV design.

I'm sure BMW would love to not be liable in those cases if they could just decide not to be liable, but inspections and fuses presumably turn out to be cheaper than the settlements they'd otherwise be paying.