Introduction

Resonant power transmission is a very special and widely used method of inductive power transmission. It is simple and effective. Here we will try to transmit electric power from one circuit to another without using direct connecting wire. Of course it will be an induction process but it is dynamic type. The maximum effective distance between transmitter and receiver will be 10 cm. This will be the first exciting step towards wireless power transmission journey just using a simple power transistor as the main component. By using this technology we can successfully charge the battery of an electric vehicle while running on a highway.

Components required

Transistor 2N3055

Resistor

Capacitor

Diode 1N4007

Coil  18 turns ( 2 strip cable )

Vero board

LED

Transformer 

Insulated copper wire

Battery 12 V

Components Description

Resistor

A resistor restricts the flow of current. The 1kΩ resistor used here is carbon film and quarter watt type. The 470Ω resistor used here is a wire wound type with 5 watt rating.

Capacitor

A capacitor stores electric charge. Capacitor used here is 470 µF and it is an electrolytic type.

LED (Light Emitting Diode)

It is a transducer which converts electrical energy into light energy.

Transistor 2N3055

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit. 2N3055 is a npn type complementary silicon power transistors. Its continuous maximum collector current rating is 15 ampere. It can withstand a maximum collector-emitter voltage of 60 volt. It is widely used in power applications. Here a proper heat sink is required, fitted tightly with the metal body of transistor.

Transformer

It consists of two coils of insulated copper wire linked by an iron core. Transformers are used to step up (increase) or step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is   no electrical connection between the coils. Here we have used a shell type step down transformer which step downs 230 volt AC to 12 volt AC. It can supply maximum 1A current. The working principle of transformer is very simple. It depends upon Faraday’s law of electromagnetic induction. Actually, mutual induction between two or more winding is responsible for transformation action in an electrical transformer.

Diode 1N4007

These are general purpose diodes. These diodes have high current capability and low forward voltage drop. The average rectified output current is one ampere.

Insulated copper wire

The wire which is made of copper and can insulate electric current is called insulated copper wire. Copper wire used in an electric motor winding is insulated with a coating of non-conductive insulation like plastic or enamel which prevents the current from passing between the wire turns. The windings of the wire multiply the effect of the circulating current due to which magnetic effect increases. The more will be the thickness of the wire, the larger current it can conduct.

Working

The power transmitter circuit operates through 12 V DC battery. The mid-point full bridge rectifier converts 12 V AC into 12 V DC and filtered by the 1000 µF capacitor. The advantage of using a mid-point rectifier circuit is, we will get full wave rectification using only two diodes instead of four. The LED in series with 1 kΩ resistor is just for power indication purpose. The output is connected to 12 V battery terminals for charging. A diode is connected in series with the positive output of rectifier circuit and positive terminal of 12 V battery to avoid continuous glowing of power indicator even when we are not charging. Use the two strip flat type copper core cable to make a coil in which the number of turns shouldn’t be less than 18 turns. Each and every turns are just look like concentric circles and the total coil must be one single cable having length approximately 5 meter. There shouldn’t be any gap between two adjacent turns otherwise unnecessarily reluctance will increase.

The transistor connects and disconnects the battery with the power sender coil around thousand times per second as per its switching frequency. As a result the coil is magnetised and demagnetised in the respective rate. In this way we get a variable magnetic field without rotating or moving the power sender coil physically. This induces a current in another coil.

Some useful terminology

Resonant inductive coupling

Resonant inductive coupling or electrodynamic induction is the near field wireless transmission of electrical energy between two magnetically coupled coils that are part of resonant circuits tuned to resonate at the same frequency.

Tuning

Adjustment of a receiver or circuit for maximum response to a given signal or frequency. Process in which one or more parameters of a device or model are adjusted upwards or downwards to achieve an improved or specified result.

Resonance

The condition of a system in which there is a sharp maximum probability for the absorption of electromagnetic radiation.

Faraday’s law of electromagnetic induction

Faraday’s law of electromagnetic induction states that whenever a conductor cuts magnetic flux, an emf is induced in that conductor. Magnitude of the induced emf is equal to the rate of change of flux linkages.

e = -N dΦ/dt

N -Number of turns of coil

Φ-flux linkage

t-time

dΦ/dt – rate of change of flux with respect to time.

Mutual induction

The production of an electromotive force in a circuit by a change in the current in an adjacent circuit which is linked to the first by the flux lines of a magnetic field.

Advantage

We can charge our car battery while running on the highway. We can save time in charging the battery. So, we can reduce our journey time.  It looks very simple. A lot of conventional wiring and connections are removed by using this method. The day to day circuit complexity is reduced. It is more economic and effective because the connecting wire cost is isolated. It is safe and not harmful for biological body.