WIRELESS CHARGING
Inductive charging (also known as "wireless 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 or run the device.
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| Magne Charge wall, handheld, and floor mount |
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.
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Series resonant inductive charging circuit. |
Greater distances can be achieved when the inductive charging system uses resonant inductive coupling.
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| Inductive Charging. The primary coil in the charger induces a current in the secondary coil in the device being charged. |
Examples
- An early example of inductive power transfer is the crystal radio which used the power of the radio signal itself to power headphones. Some such radios can even use the power of a stronger station to increase the volume of a weaker station
- Transcutaneous energy transfer (TET) systems in artificial hearts and other surgically implanted devices.
- Oral-B rechargeable toothbrushes by the Braun company have used inductive charging 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.
- At CES in January 2007, Visteon unveiled their wireless charging system for in vehicle use that could charge anything from cell phones to mp3 players.
- 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. This was also featured on later Pixi, Pixi Plus, and Veer 4G smartphones. Upon launch in 2011, the ill-fated HP Touchpad tablet (after HP's acquisition of Palm Inc.) had a built in touchstone coil that doubled as an antenna for their NFC-like Touch to Share feature.
- 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 called Qi
- Intel and Samsung plan to launch Qi wireless charging devices for phones and laptops in 2013.
- Nokia launched two smartphones (the Lumia 820 and Lumia 920) on 5 September 2012, which feature Qi wireless charging.
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| nokia-lumia-920-wireless-inductive-charger-charging |
Advantages
- Lower risk of electrical shock or shorting out when wet because there are no exposed conductors. e.g., for toothbrushes and shavers, or outdoors.
- Consistent and secure connections - no corrosion when the electronics are all enclosed away from water or oxygen in the atmosphere.
- Safer for implants - for embedded medical devices, allows recharging/powering through the skin rather than having wires penetrate the skin, which would increase the risk of infection.
- Convenience - rather than having to connect a power cable, the device can be placed on or close to a charge plate or stand.
Disadvantages
- Lower efficiency, waste heat - 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 within most portable electronics.
- More costly - Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.
- Slower charging - due to the lower efficiency, devices can take longer to charge when supplied power is equal.
- Inconvenience - When a mobile device is connected to a cable, it can be freely moved around and operated while charging. In some implementations of inductive charging (such as the Qi standard), the mobile device must be left on a pad, and thus can't be moved around or easily operated while charging.
- Standards - There are no De facto standards, potentially leaving a consumer, organisation or manufacturer with redundant equipment when a standard emerges
Newer approaches reduce transfer losses through the use of ultra thin coils, higher frequencies, and optimized drive electronics. This results in more efficient and compact chargers and receivers, facilitating their integration into mobile devices or batteries with minimal changes required. These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.
For example, the Magne Charge vehicle recharger 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).
