- Inductive charging
Inductive charging uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through inductive coupling to an electrical device, which then can use that energy to charge batteries.
Because there is a small gap between the two coils employed in each of the sender and receiver of the energy within the respective devices, inductive charging is considered a short-distance "wireless" energy transfer, despite the fact that there are typically more wires used with inductive charging than direct-contact charging, because it frees the user from having to deal with wires between the two devices. This is advantageous for many reasons.
Induction chargers typically use an induction coil to create an alternating electromagnetic field from within a charging base station, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.
Greater distances can be achieved when the inductive charging system uses resonant inductive coupling.
Inductive charging carries a far lower risk of electrical shock, when compared with conductive charging, because there are no exposed conductors. The ability to fully enclose the charging connection also makes the approach attractive where water impermeability is required; for instance, inductive charging is used for implanted medical devices that require periodic or even constant external power, and for electric hygiene devices, such as toothbrushes and shavers, that are frequently used near or even in water. Inductive charging makes charging mobile devices and electric vehicles more convenient; rather than having to connect a power cable, the unit can be placed on or close to a charge plate.
The main disadvantages of inductive charging are its lower efficiency and increased resistive heating in comparison to direct contact. Implementations using lower frequencies or older drive technologies charge more slowly and generate heat for most portable electronics. Inductive charging also requires drive electronics and coils that increase manufacturing complexity and cost.
Newer approaches diminish the transfer losses with ultra thin coils, higher frequencies and optimized drive electronics, thus providing chargers and receivers that are compact, more efficient and can be integrated into mobile devices or batteries with minimal change. These technologies provide charging time that are the same as wired approaches and are rapidly finding their way into mobile devices. The Magne Charge system employed high-frequency induction to deliver high power at an efficiency of 86% (6.6 kW power delivery from a 7.68 kW power draw).
- Transcutaneous energy transfer (TET) systems in artificial hearts and other surgically implanted devices.
- Inductive charging is used in Oral-B rechargeable toothbrushes by the Braun (company) since the early 1990s.
- Hughes Electronics developed the Magne Charge interface for General Motors. The General Motors EV1 electric car was charged by inserting an inductive charging paddle into a receptacle on the vehicle. General Motors and Toyota agreed on this interface and it was also used in the Chevrolet S-10 EV and Toyota RAV4 EV vehicles.
- In 2006, researchers at the Massachusetts Institute of Technology reported that they had discovered an efficient way to transfer power between coils separated by a few meters. The team, led by Marin Soljačić, theorized that they could extend the distance between the coils by adding resonance to the equation. The MIT wireless power project, called WiTricity, uses a curved coil and capacitive plates.
- April 28, 2009: An Energizer inductive charging station for the Wii remote is reported on IGN.
- At CES in January 2009, Palm, Inc. announced their new Pre smartphone would be available with an optional inductive charger accessory, the "Touchstone". The charger came with a required special backplate that became standard on the subsequent Pre Plus model announced at CES 2010.
- In August 2009 A consortium of interested companies called the Wireless Power Consortium announced they were nearing completion for a new industry standard for low-power Inductive charging
As mentioned above, Magne Charge inductive charging was employed by several types of electric vehicles around 1998, but was discontinued after the California Air Resources Board selected the SAE J1772-2001, or "Avcon", conductive charging interface for electric vehicles in California in June 2001.
In 2009, Evatran, a subsidiary of MTC Transformers, formally began development of Plugless Power, an inductive charging system they claim is the world’s first hands-free, plugless, proximity charging system for Electric Vehicles. With the participation of the local municipality and several businesses, field trials were begun in March, 2010, on the system scheduled to be available in fourth quarter 2010.
Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an electric transport system (called Online Electric Vehicle, OLEV) where the vehicles get their power needs from cables underneath the surface of the road via non-contact magnetic charging, (where a power source is placed underneath the road surface and power is wirelessly picked up on the vehicle itself. As a possible solution to traffic congestion and to improve overall efficiency by minimizing air resistance and so reduce energy consumption, the test vehicles followed the power track in a convoy formation. In July 2009 the researchers successfully supplied up to 60% power to a bus over a gap of 12 cm.
In one inductive charging system, one winding is attached to the underside of the car, and the other stays on the floor of the garage.
The major advantage of the inductive approach for vehicle charging is that there is no possibility of electric shock as there are no exposed conductors, although interlocks, special connectors and RCDs (ground fault detectors) can make conductive coupling nearly as safe. An inductive charging proponent from Toyota contended in 1998 that overall cost differences were minimal, while a conductive charging proponent from Ford contended that conductive charging was more cost efficient.
In 2010 onwards, car makers are signaling their interest in wireless charging as another piece of the digital cockpit. A group was launched in May 2010 by the Consumer Electronics Association to set a baseline for interoperability for chargers. In one sign of the road ahead a General Motors executive is chairing the standards effort group. Toyota and Ford managers said they also are interested in the technology and the standards effort.
Daimler’s Head of Future Mobility, Professor Herbert Kohler, however have expressed caution and said the inductive charging for EVs is at least 15 years away and the safety aspects of inductive charging for EVs have yet to be looked into in greater detail. For example, what would happen if someone with a pacemaker is inside the vehicle? Another downside is that the technology requires a precise alignment between the battery and the charging facility.
In November 2011, the Mayor of London, Boris Johnson, and Qualcomm announced a trial of 13 wireless charging points and 50 EVs in the Shoreditch area of London's Tech City, due to be rolled out in early 2012.
- Charging station
- In-road electric vehicle charger
- Resonant energy transfer
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