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By Timm Murray

Five minute EV charging is silly, and we don't need it


Big new battery breakthroughs often come with headlines proclaiming ten or even five minute charging times for EVs that can go 600 miles on a full charge. Batteries are not the full story. These charge times would require a whole new plug design, and likely entirely new transformers to power the charge banks. There are bottlenecks besides batteries.

Let’s take the Tesla Model Y’s standard size battery of 60 kWh. Let’s say it’s at 10% charge (6 kWh) and we want to go all the way to 100%. That means we need to feed it 54 kWh (assuming no efficiency loss), which can just mean giving it 54 kW over the course of 60 minutes. To do the same in 5 minutes, we have to feed it 650 kW.

Note that this isn’t even the biggest battery out there right now. It’s a modest sized car with a good enough battery.

An SAE J3400 plug (the standard being developed from Tesla’s plug) supports up to 1,000VDC and 650A of current. This means it has a max capacity of 650 kW; any efficiency loss at all will exceed the limit above. CCS plugs only support 350 kW. Japanese CHAdeMO plugs can go up to 900 kW, but they are rare outside of Japan.

Meanwhile, the transformers being built out for current EV infrastructure won’t even hit that much. Tesla V4 Superchargers are also only designed up to 250 kW. So the plug can’t support it, and that isn’t even the biggest bottleneck.

Even if the chargers and plug were redesigned, you’re not likely to see many of them for several years.

You can play with the numbers–a larger or smaller battery, or only going to 80% instead of 100%, and calculating in some efficiency loss–but the results are always between “barely possible” and “not going to work”.

We could design a whole new plug that supports higher charge rates and deploy even beefier transformers, but why? Aiming for 20 minute charge times for 250 mile range is generally more than enough even when cold weather chops 20% or even 40% off this range. That gets you 2-4 hours of driving, which is about when you should be getting out to stretch, anyway.

How much are these 600 mile range EVs going to weigh? Why not keep them at around 250 miles and use new battery tech to reduce their weight?

Instead of looking for absurd ranges and charge times, focus on what people are going to do with those 20 minutes. Many of the L3 chargers you’d use on road trips right now are in parking lots for Walmart, dealerships, or places that are equally uninteresting and unappealing. How about a nice place to sit down, get on wifi, and grab a cup of coffee? Or just walk around in something other than a parking lot?

This whole problem can go away by providing a nice experience while people are waiting.

EV charge times look a lot better if they’re combined with walkable cities.

Copyright © 2024 Timm Murray

Opinions expressed are solely my own and do not express the views or opinions of my employer.