The Charging Power of Electric Cars and Charging Stations Explained

As an electric car driver, you are probably looking for the fastest charging options, whether it's a home wallbox or a public charging station. But here is what can happen: you buy an electric car or a wallbox with a high charging capacity and after the purchase you realise that the car is not being charged at the maximum charging rate and charging ultimately takes longer than expected. 

This is very confusing and often leads to frustration, but the phenomenon can be explained. Because how quickly you can charge at a charging station depends on various factors.

The three most important factors that influence the charging power and therefore also the charging time are:

• the maximum charging power of your electric car
• the maximum charging power of the charging station or your wallbox
• the number of phases that the on-board charger of your electric car has

The weakest link in the chain determines the maximum charging power and therefore also the charging time.

Let's break it down with three examples.

Your electric car has different charging power limits for AC (alternating current) and DC (direct current) charging. 

Let's assume your electric car has a maximum charging capacity of 11 kW AC and you charge it at a 22 kW wallbox. In this case, your car will still only be able to charge at 11 kW, as the on-board charger of your electric car does not allow more. The weakest link in the chain is therefore the car. 

The same naturally applies to public DC charging stations. If your electric car has a maximum charging capacity of 125 kW DC, you can still only charge with a maximum of 125 kW at a 240 kW DC charging station.

Now let's assume you have an electric car with a maximum charging capacity of 22 kW AC, but you charge it at an 11 kW wallbox. In this case, you will still only be able to charge with a maximum of 11 kW, as the wallbox with a maximum charging capacity of 11 kW is the weakest link in the chain.

Of course, the same logic applies to public DC charging stations. If your electric car has a maximum charging capacity of 125 kW DC, you can still only charge with a maximum of 50 kW at a 50 kW DC charging station.

Let's assume you have an electric car with a single-phase on-board charger and use a wallbox with a maximum charging capacity of 22 kW. In this case, you will still only be able to charge with up to 7.4 kW, as the single-phase on-board charger does not allow more and is the weakest link in the chain. 

For an electric car with a two-phase charger, you can theoretically charge with up to 14.8 kW with this wallbox and for a car with a three-phase on-board charger, you could theoretically charge with up to 22 kW, as long as there is no weaker link in the chain, as mentioned above.

Watch out!

As mentioned in the first example, not all cars have a maximum charging capacity of 22 kW, even if they are equipped with a three-phase on-board charger. Many of them can only be charged with a maximum charging power of 11 kW. A Renault Zoe, for example, can take a maximum charging power of 22 kW, while the on-board charger of the Tesla Model 3 can take a maximum of 11 kW. Nevertheless, both electric cars have a three-phase on-board charger. The same applies to electric cars with only one or two phases.