Wireless Battery Charging

- essentials of wireless battery charging or inductive charging techniques used for transferring power to portable devices without the need for a direct connection..

Wireless battery charging or wireless inductive charging as it is also called, is a method for transferring electrical energy from a charger to a device without the need for a physical wire connection.

Wireless battery charging has many advantages in terms of convenience because users simply need to place the device requiring power onto a mat or other surface to allow the wireless charging to take place.

In view of the development of wireless charging or inductive charging, it has now come into the mainstream with many companies seeking to adopt the technology to provide a competitive edge to their products in the marketplace.

Wireless battery charging basics

Wireless battery charging uses an inductive or magnetic field between two objects which are typically coils to transfer the energy from one to another. The energy is transferred from the energy source to the receiver where it is typically used to charge the battery in the device.

This makes wireless charging or inductive charging ideal for use with many portable devices such as mobile phones and other wireless applications. However they have also found widespread use in products such as electric toothbrushes where cordless operation is needed and where connections would be very unwise and short-lived.

The system is essentially a flat form of transformer - flat because this makes it easier to fit into the equipment in which it is to be used. Many wireless battery charging systems are used in consumer items where small form factors are essential.

Wireless battery charging concept
Wireless battery charging concept

The primary side of the transformer is connected to the energy supply that will typically be a mains power source, and the secondary side will be within the equipment where the charge is required.

In many applications the wireless battery charging system will consist of two flat coils. The power source is often contained within a pad or mat on which the appliance to be charged is placed.

Wireless battery charging advantages / disadvantages

As with any system, there are both advantages and disadvantages to wireless battery charging systems.

Advantages Disadvantages
  • Convenience - it simply requires the appliance needing charging to be placed onto a charging area.
  • Reduced wear of plugs and sockets - as there is no physical connection, there are no issues with connector wear, etc. Physically the system is more robust than one using connectors.
  • Resilience from dirt - some applications operate in highly contaminated environments. As there are no connectors, the system is considerably more resilient to contamination
  • Application in medical environments - using wireless charging no connectors are required that may harbour bacteria, etc.. This makes this solution far more applicable for medical instruments that may require to be battery powered.
  • Added complexity - the system requires a more complicated system to transfer the power across a wire-less interface
  • Added cost - as the system is more complicated than a traditional wired system, a wireless battery charger will be more expensive
  • Reduced efficiency - there are losses on the wireless battery charging system - resistive losses on the coil, stray coupling, etc. However typical efficiency levels of between 85 - 90% are normally achieved.

Wireless charging standards

There are several wireless charging standards that are being developed or already on the market.

  • Qi:  : The Qi wireless charging standard is one that has come to the market earlier than some others. It is basically what is termed and inductive system using a relatively low frequency (between 110 and 205 kHz for the low power and 80 to 300 kHz for the medium power) for the power transfer. Read more about Qi wireless charging standard.
  • A4WP:  : The A4WP wireless power standard was developed a little later than the Qi standard. It uses resonance techniques along with a higher power transfer frequency of 6.78 MHz for the power, and 2.4GHz for the control signals. It also allows simultaneous charging of multiple devices. Read more about A4WP wireless charging standard.

Wireless charging has now become a mainstream technology. Initially it was a novelty, but with its applications and advantages becoming recognised, it has now become a mainstream application. It is anticipated that wireless battery charging will become very widespread, if not the most common method.

With standardised interfaces and techniques, only a single wireless battery charger will be required to charge a variety of items. No longer will a whole myriad of chargers be required. Also reliability and convenience will be improved as it is far easier to place the item to be charged on the charging mat, rather than having to use a small connector.

Although the efficiency of wireless battery charging is less than that using direct connections, the added intelligence could reduce the end of charge current, thereby reducing the overall power consumption as many normal chargers are left connected even when they are not charging.

By Ian Poole

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