Wireless Charging

Hi guys !
In this post I am going to explain how a wireless charger works.

The basic working principle of a wireless charger is Electromagnetic Induction (EMI).
When a varying magnetic field, magnetic flux in particular, is applied across a closed loop, emf is induced across the loop.
The emf induced can be found by using the Faraday's law of Electromagnetic Induction.
A coil of wires carrying current produces magnetic flux and when supplied with Alternating current produces variable flux. This variable flux when linked to another coil, emf is induced in that coil.
 To refer more on Faraday's law of EMI, click here.

The working is similar to that of a transformer, the only difference being that the flux is linked through the air, instead of the core.

The transmitter part consists of a 220/12 V or 120/12 AC transformer which reduces the voltage to 12 V.
It also consists of coil of conductors. When current passes through this coil, a magnetic flux is created. The receiver part (phone) also has a coil.
When the phone is placed close enough to the transmitter, the flux is linked through air and emf is induced across the receiver coil.
(DC cannot be used to transmit the power, as the flux created by a DC current carrying coil will not be fluctuating, and emf will not be induced in the secondary. )
This induced EMF is alternating in nature. It is rectified and by using filters, a Direct Current is obtained which is supplied to the battery.

Here, the transmitter and receiver act as a transformer but with air as a core. As air is not a ferromagnetic material, most of the flux will be leakage flux ( useless flux). Hence it is not an efficient process. Even the range of the coil is less as air can link flux only for short distances.
This was Inductive charging.

Sometimes a capacitor is placed in parallel to the inductor, to create a resonance circuit. This helps in creating flux of variable frequency. Air being the core, the problems of core magnetization and power transmitting at a particular frequency will not occur. But, here the receiver circuit must have the inductor coil and the capacitor in parallel such that their resonance frequency s the same as that of the transmitting frequency. Then and then only the power transmission will take place. Then the AC is rectified and filtered into DC which is then supplied to the battery.

Advantages of Wireless Charging:

• Free from wires. No need to plug in the wire every time you need to charge the phone and to remove it after being charged.
• Many coffee shops and cafes are giving wireless port hubs where you can charge your phone.
• One can charge multiple devices from a single transmitter. 
• Not harmful, unlike microwaves.

Disadvantages of Wireless Charging:

• As air being the core, much energy is lost. Not an efficient process.
• One cannot charge a phone that has a receiver coil set to a frequency which is different from the frequency of the transmitter.
• The whole package is costlier than the wired charger.
• The charging process takes more time to completely charge the battery than a wired charger. Even the phone gets heated up quickly.
• Not used Everywhere.  

This technology is gaining speed at a considerable speed and will be available everywhere in a few years.

Please go through this video. It beautifully explains and describes the pros and cons of this process :
https://www.youtube.com/watch?v=-_3L4Hm_2ZI