Simple Wireless Power Transmission Circuit

Wireless power is not an original idea, Nikola Tesla even experimented in it in the past!

Many products including phones, electric toothbrushes and even certain medical equipment are now wirelessly charged.

However there is always space for improvement.

This post covers how to assemble a simple wireless power transmitter and receiver circuit using readily available components.

This will help to know the process of wireless charging.

What is a Wireless Power Transmission Circuit:

A wireless power transmission circuit is an electronic circuit which transfers electrical energy from a power source to a particular device without the using cables or other physical connections.

Techniques for electromagnetic fields to transfer electricity over short or long distances are the backbone of wireless power transmission.

Inductive coupling is one common technique for wireless power transmission

Transmitter Circuit Working:

Parts List:

The output of the LM386 is a 1khz square pulse signal.

This signal is then sent to the copper coil starting an oscillation in the coils magnetic field at 1khz.

As the coils magnetic field starts to rotate it produces a strong fluctuating magnetic field around it.

Receiver Circuit Working:

Parts List:

An electromotive force (emf) is generated by the increased electromagnetic flux in the receiver coil and its amplitude changes with the number of windings and the gap between the coils.

By changing the alternating current (AC) into direct current (DC) the bridge rectifier corrects the potential difference created in the receiver coil.

Therefore the positive voltage regulator 7805 which regulates the rectified DC voltage ensures a steady and controlled output voltage.

Adjust the timing resistor R1 and timing capacitor C1 values to change the output frequency range.

By adjusting the transmitter and receiver coils the circuit gets adjusted to satisfy certain power transfer requirements.

Formulas:

1. The below mentioned formula are used to calculate the frequency of an RC oscillator circuit:

f = 1 / (2 * π * R1 * C1)

where,

• The oscillator circuits output frequency represented as f is measured in hertz Hz.
• The mathematical constant π (pi) has a value of about 3.14159.
• R1 is the circuits resistor R1s resistance expressed in ohms Ω.
• C1 is the circuits capacitors capacitance expressed in farads F.

The formulas functioning:

A resistor R1 and a capacitor C1 are connected to form a feedback loop in an RC oscillator circuit which produces a voltage that fluctuates constantly.

The relationship between the oscillation frequency and the resistor and capacitor values is given by the below formula.

2: The formula below indicates the simple connection between the parameters regulating the induced electromotive force (EMF) in a transformer or coil setup.

Induced EMF ∝ Number of Windings, Distance between Coils

The meaning of the symbol ∝ is “proportional to.”

This indicates that the induced EMF and the product of the number of windings and the distance between the coils do not always have a linear relationship.

Induced EMF:

With the symbol ε (epsilon) it is the voltage that is induced in a conductor due to a fluctuating magnetic field.

It is the voltage generated in a transformers secondary coil when the magnetic field is modified by the current flowing through the primary coil.

Number of Windings N:

• In a coil this refers to the number of wire turns.
• It works with transformers primary and secondary coils.

Distance between Coils (d):

• This signifies the distance between the centers of the primary and secondary coils.
• With a shorter distance between the coils a greater magnetic field coupling is achieved.

How the formula works:

The electromagnetic induction idea that drives the working of a transformer.

A fluctuating magnetic field is generated when the main coils current changes.

The secondary coil is then cut by this magnetic field which causes Faradays Law of Induction to be activated.

How to Build:

To build a Simple Wireless Power Transmission Circuit follow the below mentioned steps:

Transmitter Circuit:

• Put up the IC LM386 as an oscillator with square waves.
• To regulate the output frequency range connect the timing capacitor C1 and timing resistor R1.
• Start the LM386 oscillator by applying 5V to 12V of electricity.
• The coil receives a 1 kHz square pulse signal generated by the LM386.
• At 1 kHz the coil begins to oscillate producing a powerful fluctuating magnetic field.

Circuit for the Receiver:

Connect an IC 7805 positive voltage regulator and a bridge rectifier to the receiver coil.

• When the transmitter and receiving coils are placed near to each other electromagnetic flow is created.
• The distance between the transmitter and receiver coils as well as the number of windings decide the induced electromotive forces (emf) amplitude.
• The positive voltage regulator controls the bridge rectifier which corrects the potential difference generated in the receiver coil.

Conclusion:

One can learn the basic principles of wireless energy transfer by building a Simple Wireless Power Transmission Circuit which is an interacting DIY project.

Also one should look into further developments in this field and assist in the development of wireless power technology by having a basic knowledge of the parts, equations and construction details.

References:

Wireless Power Transmission System Design

Wireless power transfer