1. Automatic Wireless Charger Khatibu Mgunya and Yasin Bahati
72.
Automatic Wireless Charger
Same Secondary School
Khatibu Mgunya and Yasin Bahati
Abstract:
Wireless charger(wireless power transfer) refer to a family of techniques for delivering power without wires or contacts, our daily lives rely on a multitude of personal mobile devices, such as phone, tablets, smart watch while every new device has made our lives easier in many respects, Having to remember and manage to charge all of our mobile device is a recurring and increasingly significant burden, if we could wirelessly charge our devices ,it would alleviate this daily anxiety, and may even allow such devices to be permanently unplugged, But how can one deliver a wireless power hotspot, the answer to this is ,on charging via magnetic coupling is the best method, by using one or more coil, when an AC current traverses the transmitter coil, it create a variable magnetic field and to traverses to receiver coil and generates electric current, hence delivering power to that device.
Method:
The hardware configuration of wireless charger transfer system is basically on inductive coupling method. The complete circuit diagram of project was divided in two different sections ,the first was transmission section and second was receiving section. In transmission section ,oscillation circuit operate as push-pull devices to transmit magnetic field to the receiving coil, hence to produce electromotive force(emf).
Material used was 2N2222 transistor,LED,26AWG magnetic wires,29 resistor, battery, USB cable, Aluminium foil, selotape, mobile phone and magnet;
Procedure:
4meter of copper wire were taken and divided into transmitter section and receiver section.
The usb cover was removed to allow the surrounding of the aluminium foil on the cable wire.
After surrounding aluminium foil followed by 26AWG wire until the aluminium foil become closer with wire.
Selotape was used to surrounding the whole part of the cable.
Finally, copper wire was used to complete the section as transmission and receiver by surrounding them until the selotape become contact with copper wire.
Step1, making the transmitter coil section.   
Results:
Results from step3;when the current was supplied in the coil ,the receiver section was access the power hence the mobile phone was receive the charge wirellessly.
Hence wireless charger sollution has been realized and experimental tests have been performed in order to evaluate the the power conversion efficiency,the measured efficiency of recceiver lies within the range 96% to 99.9%,so that the overall systems can only be imputed to the magnetic coupling.we use the same setup as used by other experiments.however,we involve a variety of receiver device,specifically we have tested cellphone(iPhone5s/6s,samsung galaxy s4/s5,s6.HTC1 and tablet(samsung tab4),smartwatch(samsung gear live smart watch).
Charging time vs distance,we evaluate wireless charger multispot’s ability to charge multiple phones at various distance from the transmitter.we run each experiment with those type of mobile phone mentioned,both receiver is increased from 2ft to 50ft together,at each distance,experiment are run with different receiver positions and orientations.
From the data recoded in experiment 3,Our wireless charger can charge 6device at distances up to 50ft,where as the base line are limited to 2 devices at 50cm,wireless charger charge different types of devices simultaneously when attached to an office desk and with the user sitting at the desk.also simultaneously charged a smartwatch on the user’s wrist, an iphone in her pocket,and nearby tablet.
Conclusions:
Although in this project,an innovative design of a wireless charger has been proposed and experimental results have been shown inorder to evaluate the power efficiency,power efficiency increase of about 40% under active modulation and about 7% without modulation is provided by the proposed solution.also wireless power transfer by inductive coupling is described in the result section,in this ,power transfer about 7.4watt when the transmitter and receiver are between 1.3inches so wireless charger can be used in medical implantation,industrial and consumer electronics as were as wireless sensor network and particulary remove the troublesome plug-in process,provide an inherent electrical isolation and adapt to harsh environments.