How to calculate the charging time of an electric car

Electric cars are increasingly common and it is now not difficult to find them on the streets of our cities or parked in rest areas waiting for a full recharge. One of the aspects that still holds back the "skeptics" is linked to the autonomy of the cars and, more specifically, to the recharge time needed to "fill up on energy". Although in the studio there are increasingly effective solutions to improve autonomy, reduce bulk and, at the same time, limit parking periods, at the moment it is necessary to deal with the technology on the market.

How to calculate the charging time

Before entering completely into the topic, we need to familiarize ourselves with some terms:

current: speed of the charging flow; voltage: difference in electric potential between two points; battery capacity: maximum amount of charge that a battery can hold; charge power: battery charging speed. The calculation of the charging times is very fast: just consider the battery capacity, expressed in kWh, and divide it by the charging power (in kW). For low powers, the data is very close to reality, while for high powers the data may differ as the system slows down the charging speed by lowering it when the battery level reaches approximately 80%. Does the rule always apply? Absolutely not, it can provide a rough idea. For example, the outside temperature, too hot or too cold, can in some conditions change the charging time.| ); }

What this means in concrete?

Charging at 2.3 kW:

Tesla Model 3 75 kWh: 32 hours Hyundai Kona Electric 64 kWh: 28 hours
Tesla Model 3 75 kWh: 20 hours Hyundai Kona Electric 64 kWh: 17 hours 7.4 kW AC charging column:

Tesla Model 3 75 kWh: 10 hours Hyundai Kona Electric 64 kWh: 9 hours The most common AC columns reach up to 22 kW in three-phase, while 7.4 kW is the limit of single-phase; some suppliers, such as Tesla and Enel X, allow recharging at much higher speeds in DC, even up to 250 and 350 kW, reducing the charging time to a minimum, if the car is compatible. How long do I need to stand still to recharge for 100 km? Or, how many kilometers do I gain in 10 hours?

The answers to these questions are simple and can be summarized, respectively, as:

kWh needed for 50 km: 50 kilometers * consumption / charging speed; charging time * charging power / average consumption.


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kW vs kWh: but what changes?

As widely explained in this in-depth analysis, the difference between the two units of measurement is quite simple although, more and more often, we read doubts and inaccuracies about it.

Kilowatt (kW) is the unit of measurement of power, the maximum power that an engine can generate; is a unit of measurement that does not apply exclusively to electric motors but is also reported in the booklets of cars equipped with an internal combustion engine. It is not uncommon, especially when paying the stamp or super stamp, to hear about kW and horsepower; 1 kW is 1.36 horsepower.

But what about the kWh? While in combustion engines, energy derives from the combustion of fuel, in electric ones it is all linked to the energy supplied by the batteries. For this reason, the engine power continues to be expressed in kW, while the available energy is measured in kWh.

Electric car consumption

While in internal combustion cars consumption is measured in l / 100 km (or km / l), for electric cars the unit of measurement is adopted. kWh / 100 km. The kW are not used exclusively for performance, but are also used in the field of efficiency; in this specific case they indicate how many kWh are needed to travel a hundred kilometers. Alternatively, it is possible to find the consumption indicated as Wh / km, as Tesla does on all its cars.


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