Why does my electric vehicle charge so slowly at home?

Despite an 11 kW terminal, the charging speed of my electric vehicle at home is slower than expected. How is this possible?

When we think about installing a charging station at home, we usually think about its power. But this is far from the only factor that determines the maximum charging power that can actually be achieved.

There 4 four factors to consider:

your type of main connection: single-phase or three-phase, 230 or 400 volts (V);
the terminal type and its internal connection;
the type and power of the rectifier installed in your vehicle (more information below);
any limitations imposed by the distribution network operator (in Brussels, this is Sibelga).

These factors are intrinsically linked. All these four elements determine the maximum power at which your electric vehicle can be charged. The limiting factor will be determined by the weakest of these four elements.

It is also important to think in terms of current rather than power.

Type of network connection

Your type of network connection and the voltage to which you connect your charging station will be important, as these networks do not tolerate the same charging power.

Are you connected to the 400V single-phase network via one phase and one neutral? You will only be able to charge at a maximum of 3.7 kW, because in Brussels it is compulsory to limit your charging point to 16 amps (3.7 kW) per software.
Are you connected to the 3x230V single-phase or three-phase network? You can charge at a maximum of 7.4 kW (32 amps), as a higher-power terminal requires a neutral in your connection.
Do you have a 400V network with neutral? If so, you can install terminals of up to 11 kW (limited by software or not).

Find out more about installing home charging stations.

On-board charger

The other essential constraint is the vehicle's on-board charger, or rectifier. A rectifier is used when the direction of current is from AC to DC, and an inverter is used when the direction of current is from DC to AC. But it is the same equipment.

The vehicle's on-board charger is the device that recharges the vehicle, and into which you insert your charging cable. This charger will also define the power and voltage at which you can charge your vehicle.

The vehicle's on-board rectifier has a crucial influence on charging options.

Currently, few vehicles can charge at 22kW at low voltage, as they rarely have on-board chargers with this power. The vast majority of electric vehicles accept up to 11 kW in three-phase.

In Brussels, however, 22 kW home charging stations must be limited by software to a maximum of 11 kW.

Amperage and phases

Amperage indicates the intensity of the electric current that can flow through a surface, in this case an electric wire, per second. Imagine for a moment that your electric wire is a garden hose. The amperage corresponds to the water flow rate through the pipe.

Similarly, the on-board charger in your electric vehicle can tolerate a certain amperage. It can be 16 or 32 amperes per phase.

If your vehicle is equipped with an 11 kW charger, this means that your vehicle can tolerate a maximum current of 16 amperes per phase.
If your vehicle is fitted with a 22 kW three-phase or 7.4 kW single-phase charger, it will tolerate a maximum current of 32 amperes per phase.

It is this notion that defines the power at which you will be able to charge your vehicle.

If your vehicle is fitted with an 11 kW charger, you will be able to charge at 11 kW on a three-phase network with neutral, i.e. 3 x 3.7 kW (because 3.7 kW = 16 amps).
On-board chargers that operate in three-phase mode also operate in single-phase mode. So if your vehicle is fitted with an 11 kW charger, you will not be able to exceed a charge of 3.7 kW on a single-phase network (because 3.7 kW = 16 amps).

What does this mean?

If your vehicle is equipped with an 11 kW charger, it will therefore be impossible to charge your vehicle at 7.4 kW single-phase, as this power corresponds to 32 amperes single-phase. However, 11 kW chargers only tolerate 16 amperes per phase. In this case, you will be limited to 3.7 kW.

To charge your vehicle at 7.4 kW, it must be equipped with a 7.4 kW single-phase on-board charger or a 22 kW three-phase on-board charger, and be connected to a 7.4 kW charging point.

How do I choose my charging infrastructure?

You must choose your charging station according to the type of connection to the network, as well as to the on-board charger in your vehicle. The most limiting of these factors will define the total power at which your vehicle will be charged.

To sum up, here are the key points to bear in mind:

the type of network connection limits your choice of charging station power;
it is impossible to charge at 7.4 kW if your vehicle has an 11 kW on-board charger. In this case, only 3.7 kW (single-phase 16A) or 11 kW (three-phase 16A) charging will be possible;
vehicles with a 22 kW on-board charger can only charge at home at a maximum of 7.4 kW (single-phase 32A) or 11 kW (three-phase 16A), as a software limit is imposed on the charging station.

These limits apply to home charging stations (mode 3), and not to outdoor fast charging stations (mode 4). In this case, the maximum charging power will depend solely on the maximum power of the terminal and the type of plug/charger installed in the vehicle.