The chargers

First, how fast is that charger? There are mostly two types of public charger, Level 2 and Level 3. (Level 1 is basically just plugging into a regular outlet.) Level 2, relatively slow, is convenient for those times when you’re out at a movie or a restaurant, say, and you want to just pick up some electricity while you’re parked.

If you’re on a long trip and want to juice up fast so you can back on the highway, that’s what Level 3 chargers are for. But, with these, there are a few things you have to keep in mind. How fast is fast? With a really fast charger, some cars can go from a 10% state of charge to 80% in just 15 minutes or so, adding another 100 miles every few minutes. (Charging usually slows down past 80% to reduce harm to the batteries.) But a lot of fast chargers are much slower. Fifty kilowatt fast chargers are common but take much longer than 150 or 250 kw chargers.

The car has its own limitations, too, and not every car can charge as fast as every charger. Your electric car and the charger communicate to sort this out.

When you first plug in an electric car, a lot of information passes back-and-forth between the vehicle and the charger before any electricity starts moving, said Nathan Wang, project manager at UL Solutions Advanced Electric Vehicles Charging Lab. For one thing, the vehicle has to let the charger know how fast it can safely charge and the charger needs to respect that speed limit.

Beyond that, even if your electric vehicle can charge at up to 250 kilowatts and so can the charger, you may get less speed than that. It could be because, say, you’re at a location with six fast chargers and every one has a car plugged in. The chargers may reduce output to all the vehicles rather than overload the system, said Wang.

Of course, there could also just be random technical issues. With so much energy moving around, if anything seems like it might be wrong, the system could just put everything on hold.

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