How do wireless chargers work?

A breakthrough that took place over 100 years ago has led to the convenient new charging technology of today

(Image source: Pixabay)

When we think about electricity, many of us automatically envisage wires, whether it’s fumbling around behind the television to connect the correct cables, seeing electricians work a colourful wire maze in an electric box – or simply taking out your phone charger when your battery level becomes critical.

These days the number of wires we need for our electrical devices is reducing all the time, and wireless power can now bring life back to electronic devices without the need for a physical connection. Wireless power technology uses charged particles to pass energy between devices before it’s converted back to electrical energy.

It was Nikola Tesla who showed the world that wires weren’t essential in power transmission in 1890. Using two copper wires, a primary coil could withstand massive amounts of charge. Once at maximum charge, the voltage was sent into the gap between coils, reaching the secondary coil, which was then able to produce lightning bolts. His ‘Tesla coil’ was first to demonstrate this concept, and while the breakthrough stood alone as an amazing invention, it would be over a century before the technology was used commercially.

Now wireless charging demonstrates a range of purposes and possibilities, that varies depending on how far the energy needs to be transported. Near-field applications use magnetic fields, while further distances, such as for in-space applications, require more complex techniques involving microwaves. This is often referred to as power beaming.

Phone charging made easy

1. Phone contact

The phone is placed on or near the charging device. This will work at distances up to 45mm.

2. Magnetic charging plate

The charging plate is AC-powered. When the phone is placed on top they are connected magnetically. Inductive energy moves across the gap through a magnetic field created by the AC current.

3. Coil communication

The magnetic field created between the phone and the plate induces a voltage used to charge the phone.

4. Key components

The plate’s transmitter coil and the coil in the phone need to be close. The phone needs to be fitted with this coil for wireless charging to work. The current is converted into a high-frequency alternating current (AC) by the specialised transmitter coil and converted again by the receiver.

This article was originally published in How It Works issue 133, written by Ailsa Harvey 


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