How long does it take to charge an electric car? It is one of the most frequently asked questions for anyone who is thinking about purchasing an electric or plug-in car. Before answering, it is necessary to clarify some basic aspects.
Battery capacity
The batteries installed on vehicles are not all the same. The battery capacity is the quantity that measures how much electricity can be stored. This quantity is measured in kilowatt hours (kWh). The more kWh of a battery, the more energy it can contain (and therefore the more kilometers the car can cover with a full tank). This figure corresponds to the capacity of an old petrol car tank.
Charging power
Charging power, or even charging speed, is the quantity that measures the amount of effective energy per unit of time that is transferred from the charging station to the battery of the car. Ideally it could be equal to the power of the charging station but in reality it is almost always limited by a series of factors including:
Charging station power
The power of a charging station is the quantity that measures how much energy per unit of time the station can transfer into the battery of the car. This quantity is measured in kilowatts (kW). This number depends both on the type of column that is used and on the availability of power of the electrical network to which you connect. For example, it may happen that we have a 22 kW wallbox installed in a house where the maximum energy availability is 3 kW. In this case the maximum current of the charging station will be 3 kW.
Always making comparison with petrol cars, this quantity corresponds to how many liters per second a petrol pump can deliver.
Maximum charging power of the machine
Often the machine has a limit on the maximum power at which it can be charged and most of the time this limit is lower than the power of the charging station.
Maximum current of the charging cable
When you recharge by connecting your charging cable to an EV charging point it may happen that the maximum current allowed by the cable limits the charging power. Cables that support higher currents have a higher cost but allow you to charge faster.
Grid energy availability
With these two concepts clear, to calculate how long it will take to fill up your electric car, just apply this simple formula:
Especially in the domestic environment, the EV charging points are connected to networks with limited energy availability and therefore they are set on reduced recharge powers so as not to cause blackouts. In these cases, a load balancing system (or power management) gives a great advantage because it always allows you to use all the power available in the network by self-regulating the charging station according to the home consumption.
The result of this calculation are the hours required to charge the car battery from totally discharged to fully charged.
Some examples are shown in the table below.
Perhaps an even more interesting question on the topic of charging times could be the following: given a certain charging power, how long do I have to charge my car for extending the autonomy of about 100 km? In this case the answer is much simpler and just depends only on how much the car consumes.
If we assume an average consumption of 15 kWh per 100 km, the charging power of 3 kW will take about 5 hours to provide sufficient charge to travel 100 km. For the same charge, it will take about 2 hours at 7 kW and about 40 minutes at 22 kW.
What about your car? How long does it take to recharge at your favorite charging station?