Siemens unveils plug-free contactless system for recharging electric cars

Siemens has unveiled a system for recharging the batteries of electric vehicles that does not require an electric cable to be plugged into the recharging point.

Instead, the system uses inductive charging, in which a current flowing through an electric coil in the charging station generates a magnetic field that induces an electric current in a second coil in the vehicle, recharging the battery.

The system, demonstrated last week at the annual technology exhibition Hannover Messe, was developed in cooperation with the car manufacturer BMW. In June it will be tested live in a project funded by the German Environment Ministry and involving several vehicles in Berlin.

According to Siemens, the non-contact technology works if drivers make only a short stop to recharge. The associated charging stations can be easily incorporated into practically any setting, making them nearly invisible and protecting against vandalism and wear and tear.

The lack of an extensive and reliable recharging system is a big obstacle to the increased use of electric vehicles. Electric cars have to recharge their batteries more often than vehicles with combustion engines need to refuel, and there are a number of moves to create a suitable infrastructure, including installing recharging points in homes and car parks and setting up “battery swopping” stations where drivers can drop off a spent battery and pick up a charged one.

Siemens says its inductive energy transmission technology would make it possible to automatically recharge vehicles, such as taxis waiting at cab stands.

The charging station is connected to the public grid by a primary coil that is completely underground. A secondary coil is attached to the car, with the distance between the two coils being between eight and 15 centimeters. When the driver starts the charging process, an electric current begins to flow through the primary coil. The resulting magnetic field induces an electric current in the secondary coil, which recharges the battery.

Electricity is transmitted from the grid through all of the components to the battery at an efficiency of more than 90 percent.

The magnetic field is generated only in an exactly predetermined area between the two coils. Siemens says the system says the strength of the field in and around the vehicle is far below the internationally recommended limit of 6.25 microteslas.

Starting in May, a prototype with a charging power of 3.6 kilowatts will be tested in an electric vehicle. This test will be followed by the trial in Berlin to determine what improvements are needed to enable the technology to be integrated into mass-produced vehicles.

Siemens is also promoting the technology as a means of storing electricity from solar and wind generation, to balance the load in the electricity grid.