Inductive charging

Magne Charge wall, handheld, and floor mount

Inductive charging uses the electromagnetic field to transfer energy between two objects. A charging station sends energy through inductive coupling to an electrical device, which stores the energy in the batteries. Because there is a small gap between the two coils, inductive charging is one kind of short-distance wireless energy transfer.

The other kind of charging, direct wired contact (also known as conductive charging or direct coupling) requires direct electrical contact between the batteries and the charger. Conductive charging is achieved by connecting a device to a power source with plug-in wires, such as a docking station, or by moving batteries from a device to charger.

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.

Advantages

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 in close proximity to a charge plate.

Inductive Charging. The primary coil in the charger induces a current in the secondary coil in the device being charged.

Disadvantages

One disadvantage of inductive charging is its lower efficiency and increased ohmic (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; the technology is nonetheless commonly used in some electric toothbrushes and wet/dry electric shavers, partly for the advantage that the battery contacts can be completely sealed to prevent exposure to water. 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, 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 finding their way into mobile devices rapidly. The Magne Charge system employed high-frequency induction to deliver high power at an efficiency of 86% (6.6kW power delivery from a 7.68kW power draw).

Examples

• Transcutaneous energy transfer (TET) systems in artificial hearts and other surgically implanted devices.

• 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

Electric vehicles

Main article: Electric vehicle

As mentioned above, Magne Charge inductive charging was employed by several 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 12cm.

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.

See also

• Charging station
• In-road electric vehicle charger
• Resonant energy transfer
• Environmental technology

External links

• Concise information about Wireless Power at Whackk!
• How Inductors Work
• How Electric Toothbrushes Recharge Using Inductors
• Inductive Charging
• Wireless Electricity Is Here