What is a fast charge curve and why is it important?

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Of course, an electric car needs to be charged 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 information is decisive in this exercise: the load curve. We explain what it is, how it works and why it is important.

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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 according to plan.

Today we focus on a specific point of fast charging: load curve. We are going to recall the concepts to take into account to understand the usefulness of load 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 piece of information.

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 DC (in fast charging terminals, with cable connected to the terminal). In direct current, manufacturers usually advertise a maximum power expressed in kilowatts (kW) to print on the vehicle brochure.

For example, we can see on the Tesla site promises like ” 250 kW – maximum charge rate“. However, don’t imagine connected vehicles will charge at this power for the duration of a charge. If this were the case, a 50 kW capacity battery would be fully charged in 30 minutes with a power of 100 kW. But it’s 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: overflowing is prohibited and you must do everything possible to fill it to the brim as quickly as possible. Without a doubt, you will open the tap all the way at the beginning, when the bottle is empty, and little by little you will reduce the flow until you put the last drop without overflowing.

The principle of fast charging for an electric car is similar. The less the battery is filled, the higher the charging power. The more the battery fills up, the less it fast charges as 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 percentages take a long time to recharge. In many cars, Filling the battery from 10 to 80% takes less time than filling it from 80 to 100%..

The charging curve then represents the charging power of an electric car according to the state of charge of the battery.

Therefore, the charging curve of an electric car is not “flat” (which would mean that the power is identical throughout the duration of the recharge), but very often there is a spike (when the battery is very low charged). ), followed by a more or less linear decline as it fills up.

However, this differs greatly depending on the vehicle, as we will see below.

“ideal” load curves

Not all electric vehicle batteries are the same. Some charge faster than others or accept a different maximum charging power. The vast majority of EV manufacturers do not communicate about 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 >150 kW fast chargers and up to 50 kW with our other chargers. In the following charging curve graph, 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 charger of more than 150 kW, the charging speed is slowly reduced when the battery capacity reaches 85%.

The following charging curve shows the charging behavior of this car when the battery has optimal conditions (a temperature of around 30 °C). A colder (or hotter) battery can result in a significant drop in charging speed.

The charging output of the Hyundai Ioniq 5 // Source : Fastned

To read a charging curve, you have to look at the battery level (in abscissa) and the power (in ordinate). For example, the Hyundai Ioniq 5, at 40% battery, charging at 225 kW approximately according to the image above.

We can see that the curve is relatively flat until around 55% battery, where it drops off sharply, before gradually tapering off. Some vehicles have slightly different behaviors, where there is no plateau, but rather a continuous decline. Next we share some charging curves of different popular electric cars.

Lastly, note that these curves represent what can happen in the best of cases. If the temperature of the battery is not ideal, especially in very cold climates, the charge will be much slower, and we will tell you about it in detail in this file. In these cases, it is necessary to activate the preconditioning of the battery.

An essential fact

As you can imagine, knowing the charging curve of an electric vehicle is essential information for long trips, if you want to optimize charging time. Indeed, in some cars it may be interesting to only charge up to 50%, for example, and then cut the road until the next charger, instead of staying charged up to 90% to avoid a second charge.

Of course, this is subject to individual preferences and limitations, but charge twice ten minutes instead of once thirty minutes it can, in the end, make it possible to get to your destination much faster.

To compare two charging curves and see which car actually charges faster, you should not only look at the maximum power achieved, but above all the general shape of the curve. The less it decreases, the better the fast charging of the car will be considered.

However, other data is more relevant than simple charging power information, 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 80% faster despite its maximum power of 225 kW (18 minutes against 30 minutes in the same exercise). Especially thanks to its 800 volt architecture.

Therefore, the charging curve is useful to get to know your car better, but the most useful information in day-to-day life on long trips is the time it takes the car to charge in a fast terminal. This information is communicated most of the time by the manufacturers.

A better way to understand fast charging

In addition to WLTP range, battery size and road performance, 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 topic.

Ionity on the right, Tesla Supercharger on the left // Source: Bob JOUY for Frandroid

Ultimately, charging power is only part of the equation that makes an electric car highly efficient for long drives. In fact, consumption is also taken into account, and a car with more charging power is not necessarily the key to traveling faster. We have returned in detail to what matters during the trips of several hundred kilometers here.

Also, if you want to learn more about what you need to know when getting started with an electric vehicle, our complete guide is here for you. And don’t forget to check out our various buying guides to determine the car that’s right for you.

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