• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Need circuit help? Post them in the comments! I've answered over 50,000!

Blog | Categories | About | Contact | Calculators-online
You are here: Home / Electronics Theory / How Wireless Power Transfer Works

How Wireless Power Transfer Works

Last Updated on August 29, 2019 by Swagatam 41 Comments

Wireless power transfer is a process in which electrical energy is transferred from one system to another system through electromagnetic waves without using wires or any physical contact.

Table of Contents
  • How Wireless Electricity Transfer Works
  • The Difficulty
  • Acquiring Optimal Range
  • The Circuit Set up
  • How it Works
  • Inductor Core Selection

In this post I have explained regarding how wireless power transfer works or the transfer of electricity through air without using wires.

You might have already come across this technology and might have gone through many related theories on the Internet.

Although the Internet may be full of such articles explaining the concept with examples and videos, the reader mostly fails to understand the core principle governing the technology, and its future prospects.

How Wireless Electricity Transfer Works

In this article we'll roughly try to get an idea regarding how a wireless electricity transfer happens or works or conduction takes place and why the idea is so difficult to implement over large distances.

The most common and classic example of wireless power transfer is our old radio and TV technology which works by sending electrical waves (RF) from one point to the other without cables, for the intended data transfer.

The Difficulty

However the drawback behind this technology is that it is unable to transfer the waves with high current such that the transmitted power becomes meaningful and usable on the receiving side for driving a potential electrical load.

This problem becomes difficult since the resistance of air could be in the range of millions of mega Ohms and thus extremely difficult to cut through.

Another hassle that makes the long distance transfer even more difficult is the focusing feasibility of the power to the destination.

If the transmitted current is allowed to disperse over a wide angle, the destination receiver might not be able to receive the sent power, and could possibly acquire just a fraction of it, making the operation extremely inefficient.

However, transferring electricity over short distances without wires looks much easier and has been successfully implemented by many, simply because for short distances the above discussed constraints never become an issue.

For a short distance wireless power transfer, the air resistance encountered is much smaller, within a range of a few 1000 meg ohm (or even lesser depending on the proximity level), and the transfer becomes feasible rather efficiently with the incorporation of high current and high frequency.

Acquiring Optimal Range

In order to acquire an optimal distance-to-current efficiency, the frequency of transmission becomes the most important parameter in the operation.

Higher frequencies enable larger distances to be covered more effectively, and therefore this is one element that needs to be followed while devising a wireless power transfer apparatus.

Another parameter that helps the transfer easier is the voltage level, higher voltages allow involving lower current, and in keeping the device compact.

Now let's try to grasp the concept through a simple circuit set up:

The Circuit Set up

wireless2Bpower2Btransfer 1

Parts List

R1 = 10 ohm
L1 = 9-0-9 turns, that is 18 turns with a center tap using a 30 SWG super enameled copper wire.
L2 = 18 turns using 30 SWG super enameled copper wire.
T1 = 2N2222
D1----D4 = 1N4007
C1 = 100uF/25V
3V = 2 AAA 1.5V cells in series

The image above shows a straightforward wireless power transfer circuit consisting of the transmitter stage on the left and the receiver stage on the right side of the design.

Both the stages can be seen separated with a significant air gap for the intended shift of electricity.

How it Works

The power transmitter stage looks like an oscillator circuit made through a feedback network circuit across an NPN transistor and an inductor.

Yes that's right the transmitter indeed is an oscillator stage which works in a push-pull manner for inducing a pulsating high frequency current in the associated coil (L1).

The induced high frequency current develops a corresponding amount of electromagnetic waves around the coil.

Being at a high frequency this electromagnetic field is able to tear apart through the air gap around it and reach out to a distance that be permissible depending upon its current rating.

The receiver stage may be seen consisting of only a complementing inductor L2 quite similar to L1, which has the sole role of accepting the transmitted electromagnetic waves and converting it back to a potential difference or electricity albeit at a lower power level due to the involved transmission losses through the air.

The electromagnetic waves generated from L1 is radiated all around, and L2 being somewhere in the line is hit by these EM waves. When this happens, the electrons inside the L2 wires are forced to oscillate at the same rate as the EM waves, which finally results in an induced electricity across L2 too.

The electricity is rectified and filtered appropriately by the connected bridge rectifier and C1 constituting an equivalent DC output across the shown output terminals.

Actually, if we carefully see the working principle of wireless power transfer we find it's nothing new but our age old transformer technology that we ordinarily use in our power supplies, SMPS units etc.

The only difference being the absence of the core which we normally find in our regular power supply transformers. The core helps to maximize (concentrate) the power transfer process, and introduce minimum losses which in turn increases the efficiency to a great extent

Inductor Core Selection

The core also allows the use of relatively lower frequencies for the process, to be precise around 50 to 100 Hz for iron core transformers while within 100kHz for ferrite core transformers.

However in our proposed article regarding how wireless power transfer functions, since the two sections need to be entirely aloof from each other, the use of a core becomes out of question, and the system is compelled to work without the comfort of an assisting core.

Without a core it becomes essential that a relatively higher frequency and also higher current is employed so that the transfer is able to initiate, which may be directly dependent on the distance between the transmitting and the receiving stages.

Summarizing the Concept

To Summarize, from the above discussion we can assume that to implement an optimal power transfer through air, we need to have the following parameters included in the design:

A correctly matched coil ratio with respect to the intended voltage induction.

A high frequency in the order of 200kHz to 500kHz or higher for the transmitter coil.

And a high current for the transmitter coil, depending on how much distance the radiated electromagnetic waves is required to be transferred.

For more info regarding how wireless transfer works, please feel free to comment.

You'll also like:

  • 1.  How to Make Step Down Transformers
  • 2.  SMPS 2 x 50V 350W Circuit for Audio Power Amplifiers
  • 3.  How to Design a Buck Converter Circuit: Formulas and Calculations
  • 4.  High Voltage Constant Current Source Circuit
  • 5.  Diodes: Working, How to Use, Applications
  • 6.  Introduction to Schmitt Trigger

About Swagatam

I am an electronics engineer with over 15 years of hands-on experience. I am passionate about inventing, designing electronic circuits and PCBs, and helping hobbyists bring their projects to life. That is why I founded homemade-circuits.com, a website where I share innovative circuit ideas and tutorials. Have a circuit related question? Leave a comment.... I guarantee a reply!

Previous Post: « CDI Tester Circuit for Automobiles
Next Post: Wireless Mobile Phone Charger Circuit »

Reader Interactions

Comments

  1. Herbert Dorsey says

    August 29, 2019 at 12:21 am

    When Tesla transmitted wireless power, he used longitudinal EM radiation, which he likened to sound waves in the aether. At Colorado Springs, he lit a number of light bulbs at a receiver 26 miles away from the transmitter. He used spherical antennas which could only transmit longitudinal EM waves. This is shown on his patents for the wireless transmission of electricity.

    Reply
  2. Cinnamon says

    June 9, 2017 at 5:36 am

    okay, ive gotten a few ideas from there, now its just to figure out how to woork around the circuit design to finish the project…

    Reply
  3. Cinnamon says

    June 7, 2017 at 4:18 pm

    Swagatam thanks, i have check through the article but it still didnt give a direct way in how to go about doing the calculation for the coils, im still reading through some more article to see i can figure it out..

    Reply
    • Swagatam says

      June 8, 2017 at 2:56 am

      Did you check the following article also?

      https://www.homemade-circuits.com/2016/09/designing-induction-heater-circuit.html

      you will need to optimize the resonanace of the tank circuit to get maximum power transfer delivered across the other side…

      Reply
    • Cinnamon says

      June 8, 2017 at 5:11 am

      yeah i checked that article also and still didnt get through with it as well…

      Reply
    • Swagatam says

      June 8, 2017 at 11:12 am

      You can apply the explained principles to this circuit

      https://www.homemade-circuits.com/2017/01/high-current-wireless-battery-charger.html

      Reply
    • Cinnamon says

      June 8, 2017 at 11:22 am

      yeah Swagatam thanks, ive got an idea from this article. now i just have to develop the spec for my other circuits and put it together the the coil….

      Reply
    • Swagatam says

      June 9, 2017 at 12:13 pm

      that's right cinnamon, please go ahead…

      Reply
  4. Cinnamon says

    June 6, 2017 at 9:30 pm

    good day sir im trying to have a power transfer of about 60w, how huge would the coils be and how can i go about calculating the size that the coils need to be, really need and appreciate your help. can you please help me out?

    Reply
    • Swagatam says

      June 7, 2017 at 2:25 pm

      Cinnamon, you may have to calculate all the parameters correctly in order to implement the mentioned design efficiently and get success, you can go through the following article for all the details, and also the subsequent article:

      https://www.homemade-circuits.com/2016/09/designing-induction-heater-circuit.html

      Reply
  5. Angga Suriana says

    March 21, 2017 at 10:49 am

    Sorry sir how to expand the energy transfer distance how man..??

    Reply
    • Swagatam says

      March 27, 2017 at 3:13 pm

      Angga, increasing distance can drastically affect the efficiency of the system therefore it's not recommended

      Reply
  6. Alexis D. says

    November 30, 2016 at 7:34 am

    Hello Sir, can this circuit output 7.5v at 750mA? I need a power source for a propeller clock and this seems to be a very good circuit because I don't want to use brushes, or how can I design the circuit to get that voltage and current? best regards.

    Reply
    • Swagatam says

      November 30, 2016 at 11:35 am

      Hello alexis, yes that's possible but I am not sure how the response would be since the receiver coil would be rotating at a high speed and possibly causing some unusual effect on the induction process

      Reply
  7. Swagatam says

    October 4, 2016 at 11:49 am

    gauge is not important, it's the number of turns and a matched supply voltage which ensure a proper functioning of the circuit…gauge can be anything

    Reply
  8. shyam singla says

    October 4, 2016 at 10:08 am

    How many gauge of copper wire did I need for this project? I have tried to work with 22 gauge of copper wire, but it didn't work. So please reply fast and tell me the other basic knowledge.

    Reply
  9. Anu.... says

    October 2, 2016 at 6:54 am

    Sir, we made the circuit using ferrite core and specifications mentioned in the above circuit daigram but when we switch on the battery the transistor becomes very hot and it seems the whole voltage drop is across the transistor. ….. it would be helpful.if you could provide any solutions

    Reply
    • Swagatam says

      October 3, 2016 at 4:39 am

      Anu, please do it as per this article

      https://www.homemade-circuits.com/2016/09/designing-induction-heater-circuit.html

      Reply
  10. YN_iet says

    September 13, 2016 at 7:30 am

    Sir you mentioned that both the inductors should have 18 turns. What should be the size (diameter or area of cross-section) of the cylindrical core on which we have to wind the coil?? What should be the value of inductance of both the inductors?? Please reply sir it would be a great help.

    Reply
    • Swagatam says

      September 13, 2016 at 1:20 pm

      YN, you can try a ferrite ring, as shown below:

      coil32.net/images/img/hlp/ferrite_torroid.jpg

      Reply
  11. Unknown says

    September 11, 2016 at 12:53 pm

    If I want to transmit power over a distance of 20m wirelessly with a voltage of 220V. Please, what are the requirements in calculation and materials?
    Thank you!

    Reply
    • Swagatam says

      September 11, 2016 at 2:01 pm

      that's not feasible because it might not yield anything usable at the receiving end

      Reply
  12. Swagatam says

    September 10, 2016 at 6:06 am

    when something is wireless it has to pass through air, for wireless power transfer high amount of current needs to be passed through air, which becomes extremely difficult due to the high resistance of air…therefore presently it looks impossible.

    Reply
  13. Swagatam says

    September 9, 2016 at 3:27 pm

    yes that may be possible but the coils will need to be significantly huge, may be in the range of a couple of square meters

    Reply
  14. Swagatam says

    September 9, 2016 at 11:20 am

    No that cannot be possible, because the present wireless transmission tech requires the load to be very near to the transmitter

    Reply
  15. EXTC B4 says

    August 29, 2016 at 7:23 am

    sir, I got 3.5v at the o/p ,but to use 7805 we required min 7v..!
    so, what changes we do in the ckt so we get 7v at the o/p…?

    Reply
    • Swagatam says

      August 29, 2016 at 11:10 am

      You can try increasing the number of turns of the receiver circuit

      Reply
  16. dzormeku edward says

    July 9, 2016 at 5:42 pm

    I need a circuit diagram of transistor power energy transfer and mobile phone jammer

    Reply
  17. Alpher Fx30 says

    June 23, 2016 at 3:30 pm

    Hi Sir i have problem i try make Wireless Power Transfer.i don't kwon about wire 30 swg sir…sir i have a roller how mny cm or mm wire sir…im sorry sir b'coz x finish study but experience sir 27 years…SIR I like electronics make…TQ SIR

    Reply
    • Swagatam says

      June 24, 2016 at 1:15 pm

      Hi Alpher, you can try any suitable thin enameled copper wire, thickness is not critical since current is low…

      Reply
  18. yogesh says

    March 3, 2016 at 3:33 pm

    i need some transistor based mini project which must be different and good

    Reply
  19. Mayank Padm Bhushan says

    October 8, 2015 at 11:41 am

    Hii Sir ,
    I want to make a circuit which convert 5v 5amps into 5v 1amps . Sir i want your help please help me .

    Regard

    Reply
    • Swagatam says

      October 9, 2015 at 8:34 am

      Hi Mayank

      use a 7805 IC…however the output V might drop a bit.

      Reply
    • Ravi Mishra says

      October 25, 2015 at 3:49 pm

      Swagatam, if 7805 is used, it would only drop the output voltage. If the connected circuit draws current over 1.5 amp, 7805 itself would burn. For reducing the current rating, a ferrite core transformer with similar primary to secondary turn ratio, but having thin secondary winding wire would solve the purpose. I hope you could suggest proper calculations & other components required.

      Reply
    • Swagatam says

      October 26, 2015 at 2:31 am

      Hi Ravi, a 7805 will never burn due to overload or a short circuit, as it's internally protected for all these issues, but it will need to be adequately heatsinked for getting optimal an response from it

      Reply
    • Sumukha Bhagi says

      November 27, 2016 at 10:15 pm

      As per my knowledge, 78xx series regulators have only temperature protection circuit… Not any over voltage or current / short circuit protection.

      Reply
    • Swagatam says

      November 28, 2016 at 3:21 am

      check datasheet to correct yourself.

      78XX are all internally protected from overheating, output short-circuit, overload, and input voltages upto 35V

      Reply
  20. abhishek yadav says

    September 29, 2015 at 12:53 pm

    Sir how can I transfer 12v.

    Reply
    • Swagatam says

      September 30, 2015 at 1:48 pm

      as explained here:

      https://www.homemade-circuits.com/2015/09/wireless-cellphone-charger-circuit.html

      Reply
  21. VIJAY AJ says

    September 28, 2015 at 2:49 pm

    Sir,how much distance I can transfer this energy

    Reply
    • Swagatam says

      September 30, 2015 at 1:48 pm

      not more than 1 inch…

      Reply

Need Help? Please Leave a Comment! We value your input—Kindly keep it relevant to the above topic! Cancel reply

Your email address will not be published. Required fields are marked *

Primary Sidebar

Subscribe to New Circuit Ideas

Categories

  • Arduino Projects (87)
  • Audio and Amplifier Projects (132)
  • Automation Projects (17)
  • Automobile Electronics (101)
  • Battery Charger Circuits (83)
  • Datasheets and Components (104)
  • Electronics Theory (143)
  • Free Energy (37)
  • Games and Sports Projects (11)
  • Grid and 3-Phase (19)
  • Health related Projects (25)
  • Home Electrical Circuits (12)
  • Indicator Circuits (14)
  • Inverter Circuits (87)
  • Lamps and Lights (142)
  • Meters and Testers (69)
  • Mini Projects (46)
  • Motor Controller (64)
  • Oscillator Circuits (27)
  • Pets and Pests (15)
  • Power Supply Circuits (108)
  • Remote Control Circuits (50)
  • Security and Alarm (64)
  • Sensors and Detectors (101)
  • Solar Controller Circuits (59)
  • Temperature Controllers (42)
  • Timer and Delay Relay (49)
  • Transmitter Circuits (29)
  • Voltage Control and Protection (37)
  • Water Controller (36)

Calculators

  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator
  • Filter Capacitor Calculator
  • Buck Converter Calculator
  • Boost Converter Calculator
  • Solar Panel, Inverter, Battery Calculator
  • Wire Current Calculator
  • SMPS Transformer Calculator
  • IC SG3525, SG3524 Calculator
  • Inverter LC Filter Calculator

People Also Search

555 Circuits | 741 Circuits | LM324 Circuits | LM338 Circuits | 4017 Circuits | Ultrasonic Projects | SMPS Projects | Christmas Projects | MOSFETs | Radio Circuits | Laser Circuits | PIR Projects |

Recent Comments

  • Swagatam on Understanding SG3525 IC Pinouts
  • Dan on Understanding SG3525 IC Pinouts
  • Swagatam on High Current Wireless Battery Charger Circuit
  • Swagatam on Timer Based Cell Phone Charger Circuit
  • Nitesh Agrawal on Timer Based Cell Phone Charger Circuit

Company

  • Privacy Policy
  • Cookie Policy
  • About Me
  • Contact
  • Disclaimer
  • Copyright
  • Videos
  • Sitemap

Social Profiles

  • Twitter
  • YouTube
  • Instagram
  • Pinterest
  • My Facebook-Page
  • Quora
  • Stack Exchange
  • Linkedin
  • © 2025 · Swagatam Innovations