Kaiju
Well-Known Member
There's a few things worth talking about with respect to global competitiveness. The first is that chasing the bleeding edge is not actually the key to global competitiveness. It's better to be efficient first unless you're selling to people where the price isn't the main concern. That doesn't apply when you're selling 500k vehicles a year.
Second though is that people don't seem to realize that there's a lot more going on with respect to 800V and 400V architecture and selection is quite a lot more complicated than just being ahead or behind an arbitrary curve. One consideration is related to vehicle and battery size. Small vehicles which have relatively small batteries see more benefits from 800V systems because they don't require monstrous DCFC ratings to charge quickly and if they were amperage-limited by design then they can accept more power from existing chargers.
Larger packs that already hit the limits that chargers can deliver see less of a benefit. People talk about loss and efficiency but I'd also point out those are engineering decisions rather than architecture consequences. You can make a 400V system more efficient than an 800V system, depending on who cuts corners where. That's because resistance and losses are related to materials and the straight-up cross-section of conductors. Switch to aluminum to save money? More resistance. If you make the wires smaller in an 800V system you increase resistance. You can save money maybe by doing so, but you're erasing some of the supposed efficiency gains.
For example if you take a large wire and reduce its size so its max current rating decreases by half, its cross-section is reduced to about 55% and resistance per unit length increases by more than 3x. You've cut current by half for the same power but...uh, you haven't actually made a more efficient system. It's actually worse. But then that relationship is not linear across wire sizes. It changes in favor of higher voltage as the wires get smaller because ampacity ratings are based on the temperature ratings of insulation.
If you use the same size wire in an 800V or 400V system, yep, definitely more efficient because it's straight up less current over the same resistance. But then you're not saving any money and are in fact spending more because higher voltage is higher cost. That's one reason why 800V isn't actually cheaper if you're chasing the extra efficiency. And then...you can brute force it on a 400V system by just making stuff bigger to reduce resistance. Is that optimal? Maybe not, but it might still be cheaper depending on how much more copper costs vs that 800V inverter.
In marketing terms yeah, you can sell someone on 800V because it's a bigger number and bigger numbers are better! Unless they're charging times. Since someone mentioned the Silverado EV and charging, I suppose it's worth mentioning that one of the reasons it can take more kW in a shorter span than a Rivian is because the battery pack is gigantic, a full 50% bigger than a max pack. It's not neccessarily because 800V is that much better.
Second though is that people don't seem to realize that there's a lot more going on with respect to 800V and 400V architecture and selection is quite a lot more complicated than just being ahead or behind an arbitrary curve. One consideration is related to vehicle and battery size. Small vehicles which have relatively small batteries see more benefits from 800V systems because they don't require monstrous DCFC ratings to charge quickly and if they were amperage-limited by design then they can accept more power from existing chargers.
Larger packs that already hit the limits that chargers can deliver see less of a benefit. People talk about loss and efficiency but I'd also point out those are engineering decisions rather than architecture consequences. You can make a 400V system more efficient than an 800V system, depending on who cuts corners where. That's because resistance and losses are related to materials and the straight-up cross-section of conductors. Switch to aluminum to save money? More resistance. If you make the wires smaller in an 800V system you increase resistance. You can save money maybe by doing so, but you're erasing some of the supposed efficiency gains.
For example if you take a large wire and reduce its size so its max current rating decreases by half, its cross-section is reduced to about 55% and resistance per unit length increases by more than 3x. You've cut current by half for the same power but...uh, you haven't actually made a more efficient system. It's actually worse. But then that relationship is not linear across wire sizes. It changes in favor of higher voltage as the wires get smaller because ampacity ratings are based on the temperature ratings of insulation.
If you use the same size wire in an 800V or 400V system, yep, definitely more efficient because it's straight up less current over the same resistance. But then you're not saving any money and are in fact spending more because higher voltage is higher cost. That's one reason why 800V isn't actually cheaper if you're chasing the extra efficiency. And then...you can brute force it on a 400V system by just making stuff bigger to reduce resistance. Is that optimal? Maybe not, but it might still be cheaper depending on how much more copper costs vs that 800V inverter.
In marketing terms yeah, you can sell someone on 800V because it's a bigger number and bigger numbers are better! Unless they're charging times. Since someone mentioned the Silverado EV and charging, I suppose it's worth mentioning that one of the reasons it can take more kW in a shorter span than a Rivian is because the battery pack is gigantic, a full 50% bigger than a max pack. It's not neccessarily because 800V is that much better.
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