Wireless and mobile
Article from TÜV SÜD Journal 4/2010
 | Electric vehicles could be the driving force behind mobility in the future. A technical question undergoing intense study at the moment is how to quickly and easily charge lithium-ion batteries. A non-cable solution appears to be quite promising – but no safety standards have been written yet. |
There is hardly a safer place to be than in a car. At least when a thunderstorm strikes. Michael Faraday, an English physicist born in 1791, discovered a phenomenon that bears his name today: the »Faraday cage«: If lightning strikes a metal cage, the electricity only flows on the cage's exterior surface. In a car, the vehicle's body is charged, but the people sitting in it are safe and sound. In 1831, Faraday discovered another phenomenon that would have a major impact on the future of the automobile: A magnetic field produces electricity. The principle, known as electromagnetic induction, is used today to charge batteries without using cables. An idea that works in such devices as electric toothbrushes should now make electric cars possible.
In June 2009, the electric utility E.ON and the automaker BMW began to test the road capability of the MINI E, the electric model of BMW's MINI brand. Test drivers cover nearly 200 kilometers before they have to hook up the electric vehicle for a fresh charge of power. The weakness of conductive charging, that is, the use of cables, lies right in the driver's hands. »Handling the charging cables is considered an unpleasant experience,« says Ruth Werhahn, Head of the Group Initiative Electric Mobility at E.ON AG. »Having to store five kilograms of wet or dirt-covered cable in the trunk without ruining your clothes is not such a simple task.«
Batteries charge themselves automatically
»That is why we need a handy alternative,« says Michael Winter, an expert who is part of the e-mobility innovation project at TÜV SÜD. »In the future, inductive charging systems will facilitate efficient power transmission without having that cumbersome cable.« One potential model looks like this: A 1.5 square-meter charging mat is installed on the floor of a person's garage. The mat contains an induction coil that is connected to a source of electricity. The charging process begins automatically once the electric car pulls into the garage. The power is transferred from the charging mat to a receiving coil attached to the underbody of the vehicle – without any contact between the two points. The system could also be used in public parking places – hidden beneath the asphalt. The charging process should still be possible even if the road is covered with ice, snow or dirt.
Today, it takes four hours to complete a short-charging process using cable that will enable a vehicle to travel 130 kilometers – a relatively long period of time for everyday use. Inductive charging takes even longer because of the transmission losses that occur between the charging mat and the underbody. One possible solution would be to lower part of the underbody while the vehicle is parked as a way to speed up the charging process. The Hamburg entrepreneur Sirri Karabag, who builds electric cars based on the Fiat 500, is working on another solution. A person drives a car directly to a type of coupling device and loads the electricity into a plate located behind the front license plate. It is not clear today which method will emerge as the best one.
Eliminating threats to humans and animals
Since July 2010, TÜV SÜD has been testing a charging-mat prototype in cooperation with E.ON. »The focus of this work is the system's operational safety and suitability for daily use,« says Dr. Axel Stepken, CEO of TÜV SÜD. The charging mat is operated with the typical household level of 230 volts. The level is to be raised to 400 volts in the future as a way to shorten the charging times.
It still must be determined whether this poses a danger to humans and animals. What would happen if a cat scampered over the mat while the batteries were being charged? How hot do metallic objects located near the electromagnetic field be-come? No regulatory framework has been written yet for inductive charging methods. For this reason, TÜV SÜD is drawing up recommendations to certify developments following the introduction of standard guidelines and to eliminate dangers.
Vision »e-road«: batteries charge during the trip
In 2020, at least 1 million electric vehicles are to be rolling on German roads under a plan put together by the national government. According to the business-consulting firm Roland Berger, 10 percent of new vehicles sold around the world could be electric or hybrid cars by then. »Inductive charging is already being kept in mind today in the conception of electric vehicles,« Winter says.
Kept in mind also means looking far ahead into the future. In the »e-road« project, the University of Erlangen has teamed up with various companies from the technology, automotive and construction industries. Studies are being prepared to show how feasible it is to charge a car while driving it – by using a nationwide system of charging coils buried in the road's asphalt.