Wireless charging explained.


What is wireless charging

Wireless charging also called inductive a way to transfer current wirelessly. It works on the principle of electromagnetic induction to transfer electricity from a charger to a receiver wirelessly. The wireless charging technology has been around for a long time. It only got about 5 years to a decade ago when smartphone manufacturers started to include the wireless charging capability in smartphones. The idea of charging your phone device without a cable but just by putting it on a surface was so appealing to consumers.

How does it work

The way wireless charging works is by electromagnetic induction or inductive coupling. In the late 19th century, Nikola tesla demonstrated magnetic resonant coupling, which is the ability to transfer electricity through the air by creating a magnetic field between 2 circuits; a transmitter and a receiver.

An alternating current is sent through an induction coil (the transmitter). The induction coil is usually placed in a charging pad or mat.

As the current moves, a magnetic field is created, following Oersted’s Law. The magnetic field varies in strength because the current amplitude’s alternates continually (alternating current).

Because the magnetic field fluctuates, an electromotive force is created also known as Faraday’s law of induction. This electromotive force causes an alternating electric current in the second coil, the receiver. This AC current created in the receiving coil is then converted to direct current dc with a rectifier and is then sent to the battery to charge the battery.

The transmitter coil is in the charger/ charging matt while the receiver coils is in the device being charged, which can be a smartphone.

This works well when the distance between the transmitter and receiver coils are close. To achieve greater distances, the charging system uses a resonant inductive coupling. The difference between his and normal inductive coupling is that a capacitor is added to each coil to create 2 LC circuits with a specific resonance frequency. The frequency of the alternating current is matched with the resonance frequency.  Adding the capacitor and making the charging coils to resonate at the same frequency increases the amount of current induced to the receiver.

The larger the coil diameter, the more energy can be transferred. Smartphone charging mats have relatively small coils and suffer from slow charging speed while other chargers like car wireless chargers have massive coil diameters

Uses of wireless charging

Wireless charging is being continually used in many areas. Most notable in the smartphone industry where smartphone devices come with wireless charging capabilities. Some smartphones such as the Galaxy S10 line of phones have both the transmitting and receiver coils. Which means they can act as both chargers and receivers.

Wireless charging is also used to charge electric vehicles. WiTricity; a wireless charging company was formed form research at MIT in 2007. The research was conducted by MIT physics professor Marin Soljačić where he proved he could transfer electricity at a distance of 2 meters. The efficiency at the time was 40 %, which means that 60 % of the energy was lost during transfer. He later on created WiTricity form the research.

WiTricity’s car charging system uses large copper coils of over 25 centimeters in diameter. This allows for efficient power transfer for distances up to 25 centimeters. Using resonance inductive coupling allows for high amounts of power, up to 11 KW and an efficiency of over 92%.

The Qi standard explained

For a long time, these 3 wireless charging standard groups have been in competition. The Alliance for Wireless Power (A4WP), the Power Matters Alliance (PMA) and the Wireless Power Consortium (WPC).

The WPC has 296 members and has made the most famous Wireless charging standard. The Qi Wireless Charging Standard. Many smartphone manufactures abide by their standard for wireless charging technology. These includes companies like Apple, Google, Verizon. and a lot more.

THE A4WP and OMA decide to join forces in 2015 and created the AirFuel Alliance which now has 110 members including Dell, Duracell, Samsung and Qualcomm.

The Qi system uses a charging pad and a compatible charging device placed on top of the pad. It allows for short distance charging around 1.5 cm. The system also uses magnetic resonance coupling

The first standard released by the WPC was the;

Qi low-power specification. Released in 2009, Renamed to Qi Baseline    This is wireless charging with a maximum wattage of 5 watts. Which is pretty slow compared to today’s standards. The coils are typically 5 mm parts but can be up to 40 millimeters apart.

In 2011, the qi medium specification, which as of 2019, to attain this certification, the device must be able to deliver between 30 to 65 W charging. It is expected to eventually support 200W.

In 2015. The qi high powers specification was released. The chargers should be able to deliver up to 1 KW.

Also in 2015, WPC released the Qi Extended Power Profile EPP, which supports up to 15 W and is typically used to charge mobile devices.



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