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Technology: Charging curve for electric cars: The promised plateau

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Technology: charging curve for electric cars
The promised plateau

BMW charging curve

© press-inform – the press office

When it comes to electric cars, it’s not just about the charging power or battery capacity itself, but especially about the charging curve. But what does this charging curve actually stand for?

No other topic worries you Electric car for as much conversation as recharging. However, charging speed, battery size and battery technology are only part of the overall package, because the so-called charging curve is of fundamental importance, especially when it comes to fast charging. This is more true than ever when the electric car has a manageable charging speed of 100, 120 or 150 kilowatts. It is often pointed out that the charging curve is particularly flat after a steep climb and that the maximum speed is maintained for a particularly long time. But if an electric car can charge at a fast charging station with just 80 or 100 kilowatts, then a supposedly flat curve or a corresponding plateau is of little use because the recharging process takes a very long time. This is particularly painful when you go on a long journey in your own car, because then a hypercharger with 300 or 350 kilowatts maximum output is of no use, because the bottleneck for the charging speed remains your own vehicle.

In electric cars, the curve itself is a sign of how long the maximum charging speed can be maintained. In a diagram, the charging power is plotted on the X-axis and the charge level is plotted on the Y-axis as a function of time. This creates a curve that can have different shapes. This creates a charge status indicator for the battery, because it cannot maintain the maximum speed for a long time because it gets too warm and the individual cells are damaged in the long term.

If you place the plug in the vehicle, the charging process does not start at maximum speed, because the battery and cables first have to warm up together or even cool down in hot temperatures. Preconditioning while driving or standing still can help, as this allows you to reach your maximum speed more quickly. In some cars, such as the Lucid Air, conditioning can be started manually while driving, for example, at the touch of a button; others make this dependent on navigation to the charging station, or on some models this can be started using a smartphone app when stationary. Example: with one of the fast chargers like the Porsche Taycan, after a short start it quickly reaches the maximum speed of 270 kilowatts. This charging plateau is maintained until behind the 55/60 percent mark and then drops over levels such as 250 kW and 180 kW to just under 150 kW and beyond the 80 percent limit it becomes extremely tough for almost all vehicles.

Without appropriate preparation, even with a fast charger such as the Tesla Model 3, a Kia EV9 or the Audi Etron GT / Porsche Taycan, it takes a few minutes until the maximum charging speed of 235, 250 or even 270 kilowatts is reached. It’s no different for tired chargers like the Fiat 500 Electric or an Opel Corsa Electric, because they can refuel at the charging station with a maximum of 80 or 100 kilowatts. Depending on the conditioning, driving style or general conditions such as the ambient temperature, the maximum charging speed then starts on a fast or hypercharger. With some vehicles the climb is steeper and then often quickly downhill again; others start slower, have a longer plateau and then slowly decline again. However, for most models, the curve drops noticeably again beyond the 60 percent charging mark.