Wireless Power
9 Steps
Quarter of a million views, thanks everyone!

The power cord, I know you hate it. Sometimes, you just want to cut it apart! Well say goodbye to your power cords, because with the power of inductive coupling your device will not need to be connected metal to metal. Seemlessly your device can be charged!

This instructable will show you the basics of creating your own cheap and easy wireless power mat, which you can use to power your device through the air!

New Update: complete list of components.

Check out my new project on sending a balloon into space!!
http://www.instructables.com/id/My-Space-Balloon-Project-Stratohab-Success-High/

## Step 1: What is it? How does it work?

A few years ago MIT created a system for transferring power wirelessly. They transmitted power over a two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Back in 2006, this was a pretty cool thing. You can only imagine what the implications of something like this would be. Well, unlike most of us, we do not have the time or material goods like MIT has. So i have made this simple and easy to follow Instructable, so all of you good people can experience the joy of wireless power.

Inductive Coupling uses magnetic fields to transfer power. There is a primary coil, which generates a magnetic field. Then there is another secondary coil which is composed of a capacitor and a coil, the capacitor creates a resonant circuit with the primary and secondary coils. Seem easy? Well, before publishing this instructable I found many useful and a lot of non-useful info on the subject.

In my research I found, that to transfer power in very complicated. Once i did it I found that you do not need to go to MIT do do this sort of stuff. With a little electrical know how, this is easy.

It all starts with the transmitter. This transmitter needs to create 147.7 kHz square wave AC signal. Let me take a minute to explain this all. Level one on the frequency scale is Hertzs, then there is kHz, then MHz. MIT used a 10 mHz wave to drive there coils, but for this we will be using a 147.7 kHz signal so it does not get too complicated.

The secondary coil has a 0.02 uF capacitor. This will allow the two circuits to be coupled therefore, transferring power efficiently. The 0.02 uF capacitor is used only for this frequency, and the value of this capcitor will change depending on the frequency.

The primary coil creates a magnetic field, when another coil is placed near it, energy will be induced into it.

Be in mind that i could not get a hold of a 0.02uF capacitor so i used two 0.01uF capacitors connected together.

## Step 2: Creating the Primary Coil

The primary coil uses magnet wire, which is easy to get at RadioShack. http://www.radioshack.com/product/index.jsp?productId=2036277
We will use magnet wire as the material for our coils.

Next we need something to create the 147.7 square wave AC signal. I saw videos on youtube like this one. http://www.youtube.com/watch?v=SSgo_N-5JOg Which uses a function generator. Sadly, these cost a lot of money, so i wanted to get a low cost one, that still did the same thing, just not as high of a frequency. This http://www.sparkfun.com/commerce/product_info.php?products_id=9002 is great for what i needed. Cheap and simple.
This will be the main board to create the signal.

By using a pencil or nails on a 2 x4 and your magnet wire, you can make a pretty good coil. I did about 30-40 turns, depending on the thickness of your magnet wire. Magnet wire has a very thin coating on the top of it. To get this off you can light a match and put the magnet wire in the flame for a few seconds. Take the two ends of you coil and put it into the function generator on the top two screw terminals, one in each terminal. Polarity is not a problem right now because the signal will be AC. Now place your 0.02 uF film capacitor in parallel with the terminals you put the wire magnet ends into. Turn the function generator on and use your multimetter to get it to somewhere near 147-149 kHz by turning the potentiometers. Make sure the switch on the left of the board is set to square, and your good to go. The top to terminals will allow for an AC signal.

## Step 3: The Secondary Coil

This circuit is one of the simplest you can ever create. It is composed of magnet wire coil but smaller like the primary, a 0.02uF
capacitor also like the primary, and some leads you can attach things to. For LED's the circuit looks like that. Yet, for powering your iPod and other devices that use DC power you need a diode bridge, or rectifier which can turn AC into DC to power your portable device. Take a look for yourself that the secondary coil has an AC output which will only power LED's.

## Step 4: Testing Wireless Power Through Different Materials

Yes, I decided to go a little further because of the response that I received.

You were always told as a kid, water and electricity DO NOT MIX, and that may be true, but not with wireless power. I tested this in water. No, I did not get shocked, but you may. NO! You will not I promise. This Step shows that this type of wireless power can pass through almost anything, except metal, I know, I was sad when i found that out. I mean, for a practical use, many people have desks made of metal where the coil is. This is not good, but I digress, we must move on.

Water! I mean who would think that this kind of technology has this kind of potential! It works that same exact way as if it was not in water. It is in a plastic bag as you can see. Only to protect the electronics. Unlike WiFi which is can be weakend by walls and other things, Wireless Power is not!

## Step 5: Circuits

These three pictures I have posted are of the circuits that I used. I have also posted a third picture of a theoretical circuit (has not been tested so i am not sure if it works) which turns the received energy into DC so you can hook it up to your favorite electronic device, iPod, cell phone...

Primary Coil-The function generator is the Main circuit of the primary, but you can easily buy it from the link posted earlier. Alon with the magnet coil.

In the Secondary Coil Diagram, the only capacitor is a 0.02 uF as I explained why.

## Step 6: Data

The power coming directly from the function generator to the coil: 110.5 mW.

Maximum power efficiency achieved is 42.2%. This is a very respectable power efficiency considering a limited budget and short experimentation time period.

The following chart is a visual representation of the above data points.

The following graph represents how the power output of the secondary coil was effected by efficiency at certain distances from the primary. At three inches, the current technology outputs a value that is very minute and is not efficient enough to power much of anything. However, at zero inches, the power output is very capable of achieving the goal in the engineering objectives.

## Step 7: Extra Hardware

I have now added a AC to DC diode bridge which converts AC to DC. Then i added a Joule Theif to the diode bridge, which is a very simple circuit that can amplify input power (the Dc voltage from the diode bridge). http://www.youtube.com/watch?v=gTAqGKt64WM

This allows the LED to be lit when its father away from the coil, because the voltage going to the LED is higher. It is now able to power DC devices.

## Step 8: Extra Information

I have shown you the basics of transmitting power wirelessly over short distance. Now it's your turn to make your own and comment on how your made your Mat and what you used it to power.

-If you have access to a larger function generator you can use that in the same way we used here.

-Then you can also use the 555 timer, which can create the same kind of signal, but is a bit more complicated.

With my size coils as seen in these pictures, based on how well you can tune the frequency, your looking at an efficiency range of about 70 to 85%. The led in the secondary coil, starts to fade when it is about 2 inches away from the primary. At about five inches, it is pretty well dark, but at four inches it is still a bit lit. If the coil is turned vertical, the led is dark. Please comment if you know why it is not bright when the receiving coil is vertical.

-Here's some variables that may change the outcome:

Wire gauge - 22

Amount of Wire - 40 feet

Capacitor value in primary and secondary - 0.02 uF

input voltage - around six volts; hint; i used a irf520 mosfet to amplify the power input from the function generator, which increase the secondary voltage tremendously. I'l post some pics soon.

usage of secondary coil - a voltage meter should be used first to see if there is any voltage; then you can attach an LED. I've gotten 5v from the secondary with my circuit from a 6.3 input voltage to the primary

## Step 9: List of Components

Plastic Project Box
Function Generator
http://www.nuxie1.com/guides/fungen-v2-kit.html
IRF510 or IRF520 MOSFET
0.02µF capacitor x2
Magnet Wire (Gold for Primary, Red for Secondary)
L.E.D.
Wall Power Converter 9-18VDC
 1-40 of 685 Next »
gnimrezt88 says: Apr 9, 2013. 9:08 PM
Hi, may I know what component is used in the design for the primary coil? (The one connected with function generator and dc jack, voltage regulator?)
randomtwig says: Apr 4, 2013. 12:39 PM
The magnetic "lines" created by the primary coil are at a right angle to the plane of the coil. to set up a current in the secondary coil it must also be at right angles to the plane of the coil. if the plane of the secondary coil is at a right angle to the primary one, the magnetic flux lines just kinda go past ineffectively. The effectiveness of a magnetic flux is B x i x L x sin θ where θ is the angle between the two planes
randomtwig says: Apr 4, 2013. 12:19 PM
Hi Hi. Just wondering if the power loss across the air gap is significant enough to render this inefficient?
kleomenid says: Mar 19, 2013. 8:38 AM
Does the number of coils matter? and do the sizes of the master and slave coil matter as long as they are proportionate?
shortstheory says: Mar 18, 2013. 9:53 PM
Hey, thanks a lot for your guide! Based on this and a few other sources, I was able to make a wireless electricity system (for our school's science fair) using an IC-555 and MOSFET in place of the function generator! I'll post an instructable on the construction process in the near future.
aaronmurray says: Mar 14, 2013. 10:06 AM
Is "dimming" the receiving circuit by way of adjusting the transmitter voltage possible? Or does that mess with the tuning of the coils?
EASTCOASTEMPIRE says: Feb 21, 2013. 1:36 PM
Could you just sell me one. Need 2 inch distance to charge 5 volts.
sshroff says: Feb 6, 2013. 5:40 AM
You have specified Gold for primary and Red for secondary.What would be the length of each coil?Have you used the same gauge in both the coils at the same time?
Kuzan says: Jan 28, 2013. 9:44 AM
Been doing a project like yours,I would like to ask if the phone really charging ??How Fast ,cause in our experiment it discharges instead
ehabcharek says: Oct 22, 2012. 8:22 PM
is it possible to connect the primary coil directly to the power source and the secondary coil directly to the (for example) LED?
also, is it possible to use metals other than copper?
agis68 says: Oct 19, 2012. 11:24 PM
whata you did there was also well descibe it by Tesla itself. But well you did it to remin us this cheap and safe energy transfer. Now my question.How did you make it to give this squire with smooth corners form of your coils. How many turns is the primary and how many the secondary.

thank you for sharing
alinneker says: Sep 28, 2012. 5:02 PM
What's the calculation that can be used in the experiment?
alinneker says: Sep 28, 2012. 5:06 PM
Calculations of electromagnetic waves.
jose1522 says: Sep 23, 2012. 3:28 PM
Hi guys! I was looking for an alternative for the Frequency Generator Kit since its not available and I found that a astable circuit with a 555 timer can do the trick; however, i'm not sure about the Capacitor and resistor configurators... I used an online calculator to obtain a configuration close to the 147.7 Khz frequency and it turns out I can get 146Khz with a 470 ohm R1, 47 ohm R2 and 0.01 micro farad C . Can someone double check the math for me? Thanks!
jose1522 says: Sep 23, 2012. 3:36 PM
Sorry, another correction. R1: 33ohms, R2: 470 ohms.
jose1522 says: Sep 23, 2012. 3:32 PM
I just reallized that with a 33 ohm resistor instead of the 47 ohm one I get 148Khz frequency. Still, can someone double check it?
freakqnc says: Aug 19, 2012. 1:49 AM
Quick question for anyone willing to pitch in. I am trying to use induction coupling to transfer power from a coil to another because I only need a contactless connection. I am using this in automotive to transfer 12v from standard light wires.
I can't find any simple schematics or info on how to accomplish that though looking at info I did find I should be able to use just 2 coils and perhaps just a couple condensers and resistors... I'd appreciate if anyone could be so kind to point me in the right direction! Thanks in advance! :D
are_pit says: Feb 19, 2012. 4:09 AM
hello guys...
i'am want to know...
how the secondary receive volt from primary...
can u explain to me....
thanks you..
DonEMitchell says: Jul 31, 2012. 9:29 AM
Hi are_pit,

There is a common mis-conception that the power is transfered by induction.

This is not true. The power transfers by coupled magnetic resonance --the magnetic equivalent of Tesla's high-voltage resonance.

Check my time-line I'm still working on...

http://portal.groupkos.com/index.php?title=Near_Field_Resonance_Time-line

The coupling phenomena is more akin to nuclear magnetic resonance than common induction.

One company is already making a power-pad wireless power charger for electric vehicles.

Google the quoted term "wireless power transfer" for starts. There's lots of background, more almost every day.

Another company already announced a cell-phone wireless power antenna. See my wiki above... main page, top of the top-fifty list... Electromagnetic Coils.

Have fun... run the background... there's are hardly any experts out here yet!

DonEMitchell
Schober says: Jun 3, 2012. 11:10 AM
There are a couple of things you should know before I begin to explain how this works.

Firstly, when electricity runs though anything (not just wires) it creates a very very very small electromagnetic field.

Secondly, this electromagnetic field has a spin around the conductor relative to the direction of flow of electricity.*

Thirdly, this spin is amplified by proximity to other conductors.

Fourthly, flow creates spin and spin creates flow.

Now that you know those four things I can begin to explain.

The primary coil is a coil and not just a solitary wire because the voltage being put through it does not create enough of an electromagnetic field to transmit power. So when the wire is looped around next to itself it acts like one big wire and creates a larger field than that of a single wire.

Once the field has been increased from a few micrometers to a few inches in this manner you can start to receive power. Due to the spin created by the field any circuit (electricity has to have a place to flow) placed within it will "resonate" this spin and begin to carry electricity on its own almost as if by magic.**

But this only goes so far. This field, while stronger than before and able to generate electricity, does not have quite enough power to be able to run a device receiving power through a single wire. And so it must be passively amplified (through another coil) before it can be sent to the components you are trying to use.

Once amplified in this manner there is enough voltage flowing through the receiving coil to power the device or components it is attached to.

PS This is a relatively basic and general explanation of how this works. A more detailed description of it can be found almost anywhere.
Wireless Energy Transfer
Electromagnetic Induction
Make Presents: The Inductor (Watch the whole series of Make Presents videos they explain almost all of the basic electronics components)

*Use the Right Hand Grip rule to determine direction of spin. Hold your right hand up in a fist with your thumb up. Your thumb represents the flow of electricity down the wire. Your fingers represent the direction of spin around the wire.

** This is the principle behind an Electro-Magnetic Pulse (EMP) the pulse creates so much voltage within the target's circuitry that it overloads all of the components, and destroys any form of magnetic storage.
The Maker Now says: Jul 21, 2012. 1:14 AM
Hello,
I tried the links you've provided for the Function Generator but the links say that they are not manufacturing the products.
Is there a way to get the project done without the generator?
And how to make the secondary coil?
ausam says: Jul 15, 2012. 5:34 AM
Hi, I have a simple question. Do I need the function generator to produce AC square waves of approx.147 frequency? Can I just simply connect the primary coil to a power outlet or any other source of AC current? thanks.

PS. (pleeeaase do answer. i'm doing this for my school science fair)
akipfer says: Jul 6, 2012. 10:21 AM
hi, listen to me, i recently bought a mouse, wireless mouse, but i paid 6bucks tops
(dealXtreme) this mouse, more precisly 'http://www.dealextreme.com/p/wireless-optical-mouse-9?item=2' no quotes
I want to make it fully wireless
with no need of batteries, this mouse can't hold up so much, 2 fresh AAA baterias, 2, maybe 5 days top, and the baterryes are dead...
can i do that?
won't harm my PC? i would put the large coil 'maybe under the table, wooden table, or make a case for it, tiny , so i put the mouse on it, 24\7 on wireless'

can i do that?
mouse uses 2 AAA bateries, 3V...
sujithZis says: Jun 21, 2012. 9:35 PM
Hey guys .....im making making the instruct-able
http://www.instructables.com/id/Wireless-Ipod-Charger/?ALLSTEPS#
and i am having small doubts ............... ............

MadScientist101 says: May 5, 2011. 1:19 PM
could you use a 555ic to replace the function genorater?
robotkid249 (author) says: May 9, 2011. 2:31 PM
Yes, but it wouldn't be efficient...
1710 says: May 27, 2012. 4:20 AM
where i get the circuit?
help me
MadScientist101 says: May 15, 2011. 10:28 AM
why, surely it would do the same job but less options
Goodhart says: May 26, 2011. 2:10 PM
LM555's are power hogs...really !
The nerdling says: Jun 12, 2011. 7:14 PM
dang i have heaps
Goodhart says: Jun 15, 2011. 2:05 PM
Well, compared to their low powered cousins they are....still they are quite useful.....just not if you need to keep a battery fresh without recharge for awhile. I have a bunch of them too, as I use then for simple timing projects....
The nerdling says: Jun 15, 2011. 4:37 PM
ok
Goodhart says: Jun 15, 2011. 4:59 PM
Sorry, I just didn't want to discourage your using them...., they can be very useful for the right projects.
The nerdling says: Jun 15, 2011. 5:11 PM
you didn't disgourage me for using them
Goodhart says: Jun 15, 2011. 5:31 PM
Ok, just making sure :-)
The nerdling says: Jun 15, 2011. 5:37 PM
ok
The nerdling says: Jun 23, 2012. 6:29 PM
how can i do it?
shortstheory says: Mar 18, 2013. 9:55 PM
It is entirely possible to use 555 ICs, if you use a MOSFET to convert DC to square wave AC from pin 3 of the IC.
dmcintosh3 says: May 13, 2012. 2:53 PM
I've been working on developing a simple DIY inductive charger. I have schematic and low level details in there.

I used a PCB patterned coil for the transmitter/receiver.