• Electric cars without charging plug.

  • Electric cars without charging plug.

    • 1. April 2015
    • E-Mobility
    • Photos: Wilfried Adam
    • Text: Rüdiger Abele

    A full charge automatically: Mercedes-Benz has advanced inductive charging for electric cars to near-production standard. As a result, the charging cable will become a thing of the past.

    An electric car without a charging plug? Rather than just a fantasy, this is already close to reality. „In just a few years` time we will equip the next generation of electric and hybrid vehicles with inductive charging technology,“ says Harald Kroeger, in charge of electrical systems, electronics and electric powertrains at Mercedes-Benz Cars Development. The new technology makes charging the vehicle battery considerably easier and at the same time considerably more convenient than today. „Users no longer need to run a charging cable from the power outlet in the wall to the car to replenish the energy storage,“ Kroeger explains. „They simply park the car over a flat station and the wireless charging process starts.“ As a result, the manual „refuelling“ process for electric cars as such will disappear from the daily automotive routine.

    The charging process starts automatically when the vehicle is parked above the plate.

    The great charging convenience makes recharging the battery easier than ever before. Owners should take advantage whenever a charging station is available to recharge the vehicle, for example at home, at work or even during a break while on the road. The battery charge is replenished whenever possible – even short periods of time are worthwhile. „Our understanding is that the plate while be used more often than a cable because of its great convenience,“ says Kroeger.



    Just like today`s solutions that use plugs, the system is designed to get the most out of a household power outlet. „We are able to transfer up to 3.3 kilowatts, which is enough to fully recharge the vehicle battery in the same time it takes today,“ says Kroeger. „Transferring high capacities is a key prerequisite for using inductive charging for cars. This required considerable development work.“

    Mercedes-Benz has already advanced inductive charging technology to the point where production standard is conceivable within two to three years. The scenario calls for customers being able to order a mobile charging plate together with their new vehicle from an authorized Mercedes-Benz dealer. Its use is straightforward: the charging plate is simply put on the ground of the parking space or even attached to the floor of the garage at home, and connected to the electrical grid with a power cable. The vehicle identifies itself during the approach and the charging process starts automatically the moment the vehicle is parked in the correct position over the plate and the drive system is switched off. The use of several plates is no problem – additional plates can be placed at the office or the vacation home. The technology is also suitable for fleet operators and even for the public sphere. For example, an entire row of parking bays, either outdoors or in the company underground garage, can be equipped with the flat devices and the vehicles are simply manoeuvred over them.


    As a general rule: as the vehicle approaches, it establishes contact with the charging plate via a WLAN from a distance of about ten meters. The Mercedes-Benz logotype on the charging plate lights up. „The visual feedback on the vehicle monitor that the charging position has been reached when parking is a factor in the system`s great convenience,“ Kroeger explains. „And pinpoint accuracy is not at all necessary. Just parking as usual is all that`s needed.“ According to Kroeger, linking the system to the Mercedes-Benz Active Parking Assist system with PARKTRONIC is also conceivable.

    Pinpoint accuracy in manoeuvring is not at all necessary.

    Inductive charging technology isn`t entirely new. It has long been standard on common devices such as electric toothbrushes and is increasingly becoming standard for smartphones – the hand-held device is simply placed on a charger and recharged without plugging it in. The energy is transferred over the air by an electromagnetic field. One can think of the charger as a transformer that has been cut in half: one coil is installed flat in the car, the other one in the plate on the ground below. The necessary system is thus complete.

    Of course, the development work did not just involve the charging technology per se. The charging plate also has to be completely weatherproof and be able to withstand vehicles driving over it. By now it has passed all tests. Why then is the mat not available for purchase yet? „A car is no toothbrush. The safety requirements to achieve years of one hundred percent operational safety are considerably higher, and the remaining tests and certifications are time-consuming,“ Kroeger explains. „But we are working on the series launch at full steam.“


    The Mercedes-Benz charging plate that is placed on the ground measures about 70 by 70 centimetres and is about six centimetres high. In addition to the coil, it also houses the entire power electronics. The footprint of the vehicle coil for inductive charging is only about the size of a sheet of stationery. This means it is extremely compact – a result of all the development work that went into the Mercedes-Benz system. The entire electrical system and the electronics are designed for maximum efficiency and operate at an efficiency of 90 percent. Current plans call for using the system with household power outlets because they are available at many parking spaces. But the technology could also be adapted to high-voltage connections.

    „We have taken a big step forward with our system for inductive charging,“ says Kroeger. „It will play a role in making electric driving a simple part of daily routine.“ Because, as the expert knows, electric cars will conquer their market share.


    Inductive charging of electric cars has reached a very high level of maturity – the series launch is conceivable in two to three years. Important cornerstones to get there are:
    • Efficiency

      Inductive charging means major added convenience. This more than offsets a slightly lower efficiency of about 90 percent compared with 94 percent for wired charging. But 90 percent is already a good value for an inductive system with a maximum transfer capacity of 3.3 kilowatts – with potential for further improvement in future generations of chargers.
    • Electromagnetic compatibility

      All electromagnetic waves transport energy. Compliance with specified reference values and limits is mandatory. The Mercedes-Benz system for inductive charging remains well below the limits.
    • Automatic deactivation

      The air gap between the charging plate on the ground and the coil in the vehicle measures about ten centimetres – enough space for a cat, for example. But the charger turns off automatically as soon as it makes itself comfortable on the mat. And vehicle owners have the option of receiving a message to that effect on their cell phones.