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Wireless Battery Charger | Inductively Coupled Universal Battery Charger | Charging Batteries Without Wires | Inductive Power Transfer | Inductive Charging

Wireless Battery Charger based on Inductive Power Transfer

Inductively Coupled Universal Wireless Battery Charger based on Inductive Power Transfer - powermat-iphone-4-wireless-battery-charger-wireless-charging-mat-wireless-receiver-case-new-wireless-technology

In the future all electronic devices will be wireless powered. Small, battery-powered gadgets make powerful computing portable. The foundation of wireless charging is the well-known law of Faraday on induced voltage, widely used in motors and transformers.

The wireless battery charger should be capable of charging the most common battery types found in portable  devices today.  In addition, the charging  should be  controlled from the base station and a bidirectional communication system between  the pickups  and base  station  should be developed.

Wireless charging reduces the need for wires to charge tablets, cordless gadgets, and other portable devices. Any battery-powered gadget can be charged with a wireless adapter by simply positioning it near a wireless power transmitter or a dedicated charging station. This makes the unit cabinet still waterproof and can be kept fully sealed. Wireless charging can also significantly improve durability, in addition to the intrinsic ease that it provides, since a charge socket on the side of an appliance can potentially experience technical failure or merely from accidentally plugging an incorrect connector.

Inductive Power Systems based Wireless Battery Charger:

Inductive Power Transfer (IPT)  refers to the concept of transferring electrical power between two isolated circuits across an air gap.  While based on the work and concepts developed by pioneers such as  Faraday and Ampere, it  is  only recently that IPT has been developed into working systems.

Essentially, an IPT system can be divided into two parts;

  • Primary and
  • Secondary.

The primary side of the system is made up of a resonant power supply and a coil. This power supply produces a high frequency sinusoidal current in the coil.  The secondary side (or ‘pickup’) has a smaller coil, and a converter to produce a DC voltage.


Working of Inductive Power Transfer based Wireless Battery Charger:

In this system communications signals are encoded onto the waveform that provides power to the air gap. Communication from the primary side to the secondary is implemented by switching the power signal at the output of the resonant converter between its normal level  and a lower level which is detectable by the pickup but still provides enough power to control the pickup micro-controller. This process is called Amplitude Shift Keying (ASK). This is achieved by varying the output voltage of the buck converter which provides an input DC voltage to the resonant converter.


Communication from the secondary to the primary is achieved by a process called Load Shift Keying (LSK).  This involves varying the loading on the pickup.   Any load on the pickup will reflect a voltage on the primary circuit proportional to the load.  Therefore a variation in the load on the pickup can be detected by the charging station.

The communications system must provide two discrete levels of voltage reflected onto the primary side,  to represent the on and off states for digital communications. The difference must be easily detected on the primary side to provide a robust communications channel. Signals are decoded by simple filters and comparators which feed a  digital signal to the micro-controllers.

Wireless Battery charging standards

Several wireless charging protocols are being developed and currently available on the market.

Qi – The Qi wireless charging standard was the first to launch and has since consolidated its dominance. It has been adopted by the big handset maker “Apple,” and it is used by nearly all wireless battery charger for domestic and many other applications. It is effectively an inductive device that transfers power at a comparatively low frequency (between 110 and 205 kHz for low power and 80 to 300 kHz for medium power).

A4WP – A4WP (Alliance for Wireless Power) is a wireless power standard that was established after the Qi standard. It makes use of resonance techniques as well as a higher power transmission frequency of 6.78 MHz for power and 2.4 GHz for control signals. It can also charge several devices at the same time.

Advantages of Wireless Battery Charger:


IPT has a number of advantages over other power transfer methods  – it is unaffected by dirt, dust, water, or chemicals.  In situations such as coal mining IPT prevents sparks and other hazards.  As the coupling is magnetic, there is no risk of electrocution even when used in high power systems.  This makes IPT very suitable for  transport  systems where vehicles follow a fixed track,  such as  in factory materials handling.

Applications of Wireless Battery Charger

  1. Smart Phones, Tablets and other electronic gadgets – Consumers want simple-to-use solutions, greater positioning versatility, and quicker charging times. Typical power specifications for these applications vary from 2 to 15 watts. Interoperability across different specifications is favoured. NFC (Near Field Communication) and Bluetooth will coexist with wireless charging, making for some innovative solutions. When put back-to-back, paired phones, for example, will charge each other after negotiating the required host and customer.
  2. Accessories of wireless battery charger – Wireless power transfer can benefit headphones, wireless speakers, mouse, keyboards, and a number of other applications. Connecting charging cables to the tiny ports of ever-shrinking computers is a hardware barrier. Bluetooth headsets, for example, must be sweat-proof to survive in a gym environment. This is only possible with wireless charging.
  3. Electric Vehicles with wireless battery charger- Smart charging stations for electric vehicles (EVs) are also on the way, but they’ll need much more energy. The development of norms is ongoing.
  4. Miscellaneous – Wireless battery chargers are working their way through anything that has a battery. Remote controllers for video games and televisions, cordless power tools, cordless vacuum cleaners, soap dispensers, hearing aids, and even cardiac pacemakers fell under this category. Wireless battery chargers may also be used to charge super capacitors or some other system that uses a low-voltage power cord.

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