An electric car of course needs to charge to fill its battery. But not everything is as simple as we might think, especially when it comes to fast charging speed. A very important piece of data is decisive in this exercise: the charging curve. We explain what it is, how it works and why it is important.
New electric car drivers often have many discoveries over time with their new connected car. Whether in terms autonomy, consumption, or even charging habitsit is necessary to correctly understand the world of electromobility so that everything goes as planned.
Today, we are focusing on a specific point of fast charging: the charging curve. We are going to recall the concepts to keep in mind to understand the usefulness of charging curves, before talking about the differences that can be observed between theory and reality. Finally, we will examine the different ways of understanding fast charging thanks to this essential data.
A concept to keep in mind
Charging an electric car can generally be done in two ways: alternating current (at home, or at so-called “slow” charging stations), or direct current (on fast charging terminals, with cable attached to the terminal). In direct current, manufacturers often announce a maximum power expressed in kilowatts (kW) to impress on the vehicle brochure.
For example, we can see on Tesla’s site promises like ” 250 kW – maximum charging rate“. However, do not imagine that connected vehicles will charge at this power for the duration of a charge. If this were the case, a battery with a capacity of 50 kW would be fully charged in 30 minutes with a power of 100 kW. But it is not that simple.
An easy way to understand the principle of a recharge curve is as follows. Imagine that you have a bottle of water to fill at the tap, with two instructions to follow: it is forbidden to overflow, and you must do everything to fill it to the brim as quickly as possible. You will undoubtedly open the tap fully at first, when the bottle is empty, and gradually reduce the flow until you put the last drop without overflowing.
The principle of an electric car fast charge is similar. The less the battery is filled, the higher the charging power. The more the battery is filled, and the less it charges quickly, since it should not exceed 100% battery.
In practice, it is for this reason that it is often better not to charge up to 100% when traveling, because the last few percents take a very long time to recharge. On many cars, Filling the battery from 10-80% takes less time than filling it from 80-100%.
The charging curve then represents the charging power of an electric car according to the state of charge of the battery.
The charging curve of an electric car is therefore not “flat” (which would mean that the power is identical over the entire duration of the recharge), but there is very often a peak (when the battery is very lightly loaded), followed by a more or less linear decrease as it fills.
However, this differs widely depending on the vehicle, as we will see below.
“Ideal” charging curves
Not all electric vehicle batteries are created equal. Some charge faster than others, or accept a different maximum charge power. The overwhelming majority of electric vehicle manufacturers do not communicate on charging curves of their cars, so it’s up to users to find out what’s behind the promises of each car.
Fortunately, the fast-charging operator Fastned makes the charging curves of many vehicles available on its website, which constitutes a very interesting database. Here is for example what we can read about the Hyundai Ioniq 5:
The charging speed of the IONIQ 5 Long Range is up to 232 kW with our fast chargers >150 kW and up to 50 kW with our other chargers. On the charging curve graph below you can see the charging curve with both types of chargers. On average, the IONIQ 5 Long Range charges 100 km of range in 5 minutes (>150 kW charger) or 30 minutes (50 kW charger). With a 150+ kW charger, the charging speed slowly slows when the battery capacity reaches 85%.
The charging curve below shows the charging behavior of this car when the battery has optimal conditions (a temperature around 30°C). A colder (or hotter) battery can result in a significant drop in charging speed.
To read a charging curve, you have to look at the battery level (on the abscissa) and the power (on the ordinate). For example, the Hyundai Ioniq 5, at 40% battery, charging at 225 kW approximately according to the picture above.
We can see that the curve is relatively flat until around 55% battery, where it drops off sharply, before gradually decreasing. Some vehicles have slightly different behaviors, where there is no plateau, but a continuous decrease. Below we share some charging curves of different popular electric cars.
Finally, keep in mind that these curves represent what can happen in the best case. If the battery temperature is not ideal, especially in very cold weather, the charge will be much slower, and we told you about this in detail in this file. In these cases, it is necessary to activate the preconditioning of the battery.
An essential piece of data
As you can imagine, knowing the charging curve of an electric vehicle is essential data for long trips, if you want to optimize the time spent charging. In effect, it may be interesting on some cars to only charge up to 50% for example, then cut the road until the next charger, rather than remaining charged up to 90% in order to avoid a second charge.
This is of course subject to individual preferences and constraints, but charge twice ten minutes rather than once thirty minutes can, in the end, make it possible to arrive at your destination much more quickly.
In order to compare two charging curves and check which car actually charges faster, you must not only look at the maximum power reached, but above all the overall shape of the curve. The less it decreases, the better the fast charge of the car considered.
However, other data is more relevant than simple information on the charging power, such as the duration to fill the battery from 10 to 80%. Although a Tesla Model 3 Grande Autonomie accepts up to 250 kW of power, a Kia EV6 will go faster at 80% despite its maximum power of 225 kW (18 minutes against 30 minutes on the same exercise). Especially thanks to its 800 volt architecture.
The charging curve is therefore useful for getting to know your car better, but the most useful information on a daily basis on long journeys is the time the car takes to charge on a fast terminal. This information is most of the time communicated by the manufacturers.
A better way to understand fast charging
In addition to WLTP range, battery size and performance on the road, knowing the fast charging capabilities of an electric vehicle can be decisive when making a purchase. Information is not always easy to find, but Fastned support has a pretty good database on this subject.
Finally, the charging power is only part of the equation that makes an electric car very efficient in carrying out long journeys. Indeed, consumption is also taken into account, and a car with more charging power is not necessarily the key to faster travel. We have gone back in detail to what matters during the journeys of several hundred kilometers here.
Also, if you want to learn more about things to know when starting out with an electric vehicle, our comprehensive guide is here for you. And don’t forget to consult our various buying guides to determine the car that is right for you.
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