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Electric cars and charging losses: so much electricity is wasted

When charging the e-car, not all of the electricity reaches the battery. But how high are the charging losses and what are the differences between household sockets and wallboxes?

The ADAC measured and found major differences and, in some cases, massive charging losses. In addition to charging at the socket with 2.3 kilowatts, e-car owners can charge at their wall box with up to eleven kW - in some cases even with 22 kW. There is also the option of operating on the wall box with reduced charging capacity. The latter can occur when charging multiple vehicles or using electricity from the photovoltaic system.

Four e-cars in the test

The car club used four models for the test: Renault Zoe, VW ID.3, Tesla Model 3 and Fiat 500e. The Renault Zoe has the highest charging loss at the socket with 24.2 percent.

For all four test vehicles, the measurement results are in favor of the wall box. The Fiat 500e manages the lowest load loss on the eleven kW wall box with only 6.3 percent.

Charging losses at the socket

For charging at the household socket, the on-board charger has to convert the alternating current into direct current. Load losses already occur here. In addition, the twelve-volt on-board network consumes electricity, since various control units are active during charging. The components for controlling the charging process require between 100 and 300 watts.

The cable to the socket can also contribute to the losses, according to the ADAC, losses of up to four percent are possible and also permissible. However, house distributors, charging cables, high-voltage cables and batteries in cars only have a minor impact. Overall, the charging losses at the household socket add up to ten to 30 percent .

Charging losses at the wall box

The charging power is higher here and takes place in three phases. The supply line is designed to be stronger, but there are still charging losses during conversion in the on-board charger.

Since the battery is charged faster via the wall box, the operating times of the auxiliary consumers are also shorter. Accordingly, the charging losses at the wallbox add up to five to ten percent .

How to avoid charging loss?

The higher the charging power, the shorter the charging process and the lower the losses. The ADAC recommends charging the e-car at the wall box with maximum charging power. The charging hub makes hardly any difference - for example, whether the battery is charged by 20 or 50 percent. In concrete figures, this means that if you consistently charge the Renault Zoe at the wall box, there are 14.3 percent fewer charging losses. With a mileage of 10,000 kilometers, this would save 120 euros a year on the electricity bill. By the way: When charging at the public charging station, the electricity is not converted in the vehicle but in the charging station. The charging losses are therefore incurred by the operator. However, the temperature control of a battery that is too hot or too cold consumes additional power.

You can see a market overview of all electric cars in our slide show.

Conclusion

The charging losses at the household socket are higher compared to the wall box. The ADAC is therefore calling on manufacturers to make charging losses transparent, to improve the efficiency of on-board chargers and to shut down the 12-volt on-board system to an absolute minimum during a charging process. With AC charging in particular, there is great potential for saving energy - also because this form of charging is used very frequently.

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