1mo ago

What Are The Differences Between 400- And 800-Volt EVs? - Jalopnik

www.jalopnik.com What Are The Differences Between 400- And 800-Volt EVs? - Jalopnik

800-volt EVs are more efficient and lighter than 400-volt EVs, but they cost more to make. And their technology, being newer, is less proven.

One of an 800-volt system's greatest benefits is that it requires half the amperage of a 400-volt system to return the same charging speed, as multiplying voltage by amperage provides the charging speed. Higher charging rates incur more losses, so by lowering the current and raising the voltage, the whole process becomes more energy efficient.

Another win for the 800-volt system is that, due to the lower amperage current within the EV, thinner cables can be used.

8 comments

400 volts.

And the torque of a motor is proportionate to the square of the voltage
So it's not producing twice as much torque, it's producing four times as much
- But that doesn't matter in case of EVs, since 800/400V refers to the battery voltage. The motors are driven by variable voltage and frequency AC that is completely decoupled from the battery voltage.
  
  I wouldn't say it doesn't matter. If your motors are rated for the full voltage (and why wouldn't they be?), they will have higher maximum torque. Or you can use smaller, lighter motors.
  I haven't worked with EVs, so l but I did quite a bit with stationary, industrial, synchronous motors driven by VFDs. In that application, the V/f curve is used mostly to control torque and power efficiency. But the voltage drop isn't that dramatic.
  I imagine the EV brain would do clever things such as increase voltage to accelerate the car, while reducing it in cruise to reduce power draw. But there are clear advantages to having a higher voltage battery.
  
  TIL
- But with half the amps (and x 4 torque) it must thus rotate way slower?

A bit more technical detail from greencarreports. I was wondering if 800v charging necessarily implies anything about motor voltage, and apparently it's "sometimes".
GM’s GMC Hummer EV, for instance, runs at 400 volts, and each layer of its dual-layer battery pack operates in some ways as an individual pack. In 400-volt charging, the packs are connected in parallel, but for 800-volt charging a switch allows them to be connected in series—like the cells in a long, multi-cell flashlight—to take advantage of the higher voltage.
That 800-volt “trick” permits the Hummer EV pickup, with its 205-kwh battery pack, to charge at 350 kw and gain nearly 100 miles of range in 10 minutes—despite its 400-volt system and its inefficiency compared to other EVs.

8 comments