Curious if anyone has seen any papers about, or if you have any thoughts on what the theoretical upper limit might be for pack voltage while in DC charging configuration? Would it be technically possible to run multi kV potential through the physical format of NACS using present-day cabling and conductor materials, provided the charging hardware could match it?
I think we’re near the technical threshold right now. The gear required on the car end would just be nuts at your proposed multi-kV level. Insulation is an issue, switchgear is an issue, and battery chemistry is an issue as single-cell voltage isn’t likely to exponentially increase anytime soon, so there’s an upper limit there as well.
On the supply side, you have issues because the grid voltage locally where you need it isn’t high enough to effectively step up to a multi-kV level without a couple of transformers. You could move charging closer to substations that have higher input voltage, but you’d need new mini-grids to power the chargers.
There’s also honestly just not much of a reason to go ultra-high voltage. Maybe marginally faster charging, but that’s quickly becoming a non-issue with current systems and more abundant chargers. The cost to make the switch to multi-kV just isn’t justified by any minute advantages you’d gain.
@chozen
Also, the power electronics to handle multi-kV gets trickier and trickier. You’ll eventually be restricted to a smaller subset of devices and run into trade-offs like lower switching frequencies in inverters and converters.
When you get noticeably above 1kV, you run into serious insulation (read: cost) issues. At some point, the insulating properties of air break down, and you have to take a lot of extra care not to create shorts that way. For comparison, check out the heft of the plugs (and cables!) that will be used for the megawatt charging infrastructure for trucks (which is specified to a max of 1.25kV). That’s not something your average granny can wrestle.
Like many things, when you keep going in a direction that seems positive, you start to find unanticipated consequences. I work in an electrical utility and see voltages and currents that are unimaginable in the EV world.
Insulation resistance is the #1 issue that will bite you when you go up to higher voltages. Cables need to have special semi-conducting layers of insulation to dissipate voltages before the true insulation, then another layer to protect the insulation from mechanical damage. That is totally impractical when you need to plug in a charger.
Then again, when I was in university in the 1980s, we were told, unequivocally, that the maximum speed of data through a phone line (bandwidth limitations due to physical layout of the conductors) was 2400 baud. Within 5 years, 56 kb modems were standard, and another 5 years later, those same cables were being used for DSL at 500 mB/s.
Technology advancement is amazing when it has commercial possibilities!
What’s crazy is Wikipedia covers NACS in detail, with references.
sorphia said:
What’s crazy is Wikipedia covers NACS in detail, with references.
Why would that be crazy?? It’s an official and public standard. Would be crazy if it wasn’t on Wikipedia.
@Mark
I think he meant OP should have just gone JFGI.
https://en.wikipedia.org/wiki/Megawatt_Charging_System
The most ambitious standard I know of is 1.25kV @ 3kA for a total of 3.75MW.
Which is rather a lot.
I think a better question is “how much is enough”. I feel like we are mostly there for most applications. The Ioniq 6 can offer about three hours of driving with about 18 minutes of recharge time. I don’t know about your family, but we rarely go longer than two hours before someone needs a pee. And our average stop is at least 20 minutes.
Yes, there are still edge cases. Long-haul trucking (which should be trains instead), flight, and ocean-going ships. But even then, those are more limited by the weight of the batteries themselves. Irrespective of charging time.
@zendaya
MWCS is specifically for trucks - not for passenger cars.
Interestingly enough, NACS is an engineered standard, developed by engineers, and all of the limits of its capabilities are written in English and publicly available.
TLDR: We’re not theorizing about NACS. It’s already an accepted standard with defined limitations.
Also, those limitations are above and beyond what’s currently practical for passenger EVs, so it’s very future-proof for the intended application.
The CHAdeMO 3.0/ChaoJi standard specs 1500V at 600 amps for the low-power version intended for cars and motorcycles, so probably safe to bet the Chinese believe that 1000 to 1500 volts for consumer vehicles is possible. Afaik no one has built it in production yet, though.
They’re also working on megawatt charging that should build on the same ChaoJi system, but details are even more scarce.
@Peggy
>probably safe bet the Chinese believe that 1000 to 1500 volts for consumer vehicles is possible.
Give it a few days and it will be announced. Not consumer vehicles yet, but it is BYD.