BMW developing wireless inductive charging system for electric vehicles
By David Szondy
July 8, 2014
Electric vehicles and plug-in hybrids may be green and sustainable, but that doesn't mean much if you forget to plug them in the night before. To overcome this frustrating morning surprise, BMW Group is developing a new generation of wireless inductive charger technology that’s comparable in speed to cables, but requires no more effort than parking and pressing a button.
BMW sees premium market electric cars as a major part of the automotive future. The company already has its all-electric i3 and i8 plug-in hybrid sports car, both of which are designed for quick charging using the BMW i Wallbox. Now the company wants to take this a step further with an induction charging system as a way to make electric cars more attractive to the public.
The new induction system is designed to work with the BMW i car batteries and those under development by the company. In addition, Daimler and BMW have entered into joint development of standardized inductive chargers with the aim of making electric cars more mainstream. Inductive charging has the advantages of being user friendly and there’s no need for connectors, which BMW sees as the crucial advantage of the new charger.
Not having connectors means one less thing to remember and one less thing to suffer from mechanical wear. Without the need for a connection, the driver has only to drive over the charge station, activate it with a press of a dashboard button. The system then does the rest while keeping the driver updated on charge status and time remaining by means of a Wi-Fi connection between charger and car and a smartphone app. BMW says the app can even help the driver park the car properly over the charger.
How it works
The system consists of two components – a primary coil that is installed in a base plate on the floor of a garage or car port, and a secondary coil that is installed in the floor of the car. Both coils are circular to keep them compact, lightweight, and the magnetic field confined to a small area for safety. An alternating magnetic field in the primary coil transmits power to the secondary coil at a rate of 3.6 kW, which is enough to fully charge the high-voltage batteries in many plug-in hybrids in under three hours.
BMW says that the prototype system has an efficiency of 90 percent and can charge the BMW i8 in less than two hours. To make the charger suitable for all electric cars instead of hybrids, the company is working on boosting the charge rate to 7 kW, which would charge a BMW i3 overnight.
Since all the system's conductive components are protected, weather conditions don't have an effect on the power feed, meaning it can be installed indoors or out. The system continually monitors the space between th primary and secondary coils, so that If a foreign object enters the field, the system cuts out automatically.
BMW says its medium term goal is to put into production a user-friendly inductive charging system that is reliable and non-wearing that will be compatible with the batteries in its existing i cars, as well as the high-voltage batteries in future plug-in hybrid models.
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