jandjmh.bsky.social
11 posts
26 followers
99 following
Conversation Starter
comment in response to
post
If you got this far - thanks for reading. If you have thoughts on legit reasons why 800 volts is decidedly better, I'd love to hear them
comment in response to
post
Control circuits: 400V semiconductors are more common, less expensive, and can conduct higher currents with lower losses than 800V semiconductors.
Given that current at 800V are half as much, this is mostly a wash for the two possible choices.
comment in response to
post
Wires in the car: a clear advantage for 800V. They can be thinner and lighter. That saves a few kg. Not insignificant. But not something that would have a notable effect on any performance aspect of the car.
comment in response to
post
Motors: The difference between and 800 and 400 volt motor is simply more turns of thinner wires in the windings, or fewer turns of thicker wires. The power per volume or per kg is nearly independent of the operating voltage.
comment in response to
post
The same logic applies to power delivery. If the pack has 200 cells, and is delivering 200 kW, that's 1 kW per cell, and that number is independent of whether the cells are arranged as 400 or 800V.
BTW, the number of cells may be much greater than 200, but the same logic applies.
comment in response to
post
400 volt pack needs twice the current, the current per cell is the same as the 800V pack. Bottom line: there is no reason an 800V pack can charge faster than a 400V pack - unless the limit is in the charging cable.
comment in response to
post
The same cells, with all 200 in series would make 800 volts.
During charging, all the current in the 800V arrangement would go through every cell. In the 400 volt arrangement half the current goes through each cell. The 800V pack only needs half the current for a given power, but the although the
comment in response to
post
And once inside the car, it makes almost no difference if the battery is arranged as 400 volts or 800 volts. The battery is made up of many cells. Let's arbitrarily say 200.
Each cell is ~4 volts. A 400 volt pack would have 100 instances of 2 parallel cells, put in serie to make 400 volts.
comment in response to
post
That's nice - but Tesla's cables can deliver 250 kW at 400 volts, and few if any cars can absorb power at that rate or higher for more than a few minutes. EA chargers can deliver 350 kW, but only at 800V. At 400 volts their 500 amp limit restricts them to 200 kW.
comment in response to
post
800 volt battery achitectures have both upsided and downsides. The "more is better" vibe leads too many people to assume 800V is inherently superior. It is not.
The single biggest advantage is that for a given charging power, the amperage in the charging cable is half as much.