zlacker

Yikes, that sounds dangerous.

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

>>ameliu+(OP)
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.

>>ameliu+(OP)
> 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.

>>Kirby6+Eb
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)?

>>ameliu+Yo
Charging speed is directly related to the voltage of the pack. Even if your own vehicle had arm-thick cables to support high speed charging at 48v there is no quick charger in the world that could support it. You would be stuck in the bad old days of needing hours to recharge the battery on your EV.

>>ameliu+Yo
Both as you mentioned. Charge circuitry for DCFC can be >200kW.

Motors, for instantaneous current, can easily exceed 100kW, some much much more than that.

Even assuming limitations to 100kW (which, would be very low for motor current), that's still 2000 amps at 48V. Remember, 100kW is ~134 hp.

>>jandre+xz
No it's not, only in a practical sense. If you truly had 'arm thick cables', you could definitely charge a 48V battery just as fast. Practically speaking, though, you don't do this because every becomes so unmanageable that you can't build a charger, bus bars, etc, that would be able to match the charging speed.

>>Kirby6+mP
The problem isn't the cables in your car, it is the cable between the DC fast charger's transformer and your car. They are already thermally limited, which is why you need higher voltages to support faster charging.

>>jandre+zT
Like I said, this assumes you use ridiculous cabling and bus bars. You could design something that handles this, it would just be wildly impractically large and cost way too much money.

Also, the problem is definitely also the cables in your car. Moving to 48V would mean amperage would increase by 10-20x, which would mean cabling thickness would have to increase substantially.

>>jandre+xz
I wouldn't see why not. A battery is internally a series-connection of lower voltage batteries.

>>ameliu+(OP)
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!

>>quickt+Ox3
And if you do ever open up a car battery pack the first order of battle is to split it in half.