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Hi and welcome to my first instructable!

I'm going to show you how to make your own low-power wireless charging circuits that will let you pass electricity through the air (or any other non-metallic medium) over short distances. This is suitable for wireless battery and capacitor charging and powering of very small un-buffered circuits (such as a single LED).

Please make sure to check out the last page as there are tons of references and other sources I managed to gleam from the internet and other instructables. Also note that I spent a GREAT deal of time experimenting and researching to get this right. I'm an electrical engineer, and even still it took quite a while to get my head around some of the technical challenges. As such this is for experienced hobbyists only, unfortunately it's not easy to do although I tried to make it as simple as possible. It doesn't take a lot of skill, just a lot of tinkering to get it to work right.

Now there shouldn't be current patents on any of this (Tesla, Colpitts, Cockcroft, and Walton all made this stuff yeaaaaars ago), but I would look into it first if you wish to sell anything using this design.

If you want the circuit then just skip ahead to step 2 and ignore the theory part :).

Step 1: Theory of Operation

The short story: this is a Cockcroft-Walton generator hanging off a resonant transformer. If you don't mind wasting a couple minutes with detailed theory then charge ahead intrepid reader! Otherwise skip to the next step.

The long story, well, it's not much longer. Take a coil, make it resonate at a particular frequency using a capacitor, then place it near a similarly tuned coil and use the oscillating magnetic field of the first to cause the second to resonate. Use a clever AC to DC converter and voila, you have a method of wireless energy transfer.

After some sleuthing on the internet, I went about devising the first part, an oscillator. Various homebrew methods have been used (see: Wireless Power Instructable) but weren't very good or just temporary solutions. I used the suggestion on wikipedia of using a Colpitts oscillator. This is a decent solution because it's dead simple to build and, most importantly, it's a current oscillator and not a voltage oscillator. As current through an inductor is what generates the magnetic field, this is what will drive both coils.

The second part is fairly easy to understand, that being the two coils. Although they don't have to be the same physical size, they do need to resonate at the same frequency. The combination of number of turns and diameter determine the inductance, and some capacitors were added to obtain the correct oscillating frequency. It gets tricky when you get into the details however (and they get very, very detailed, so I won't put the majority down here) as you need to select the diameter of wire to go with the amount of current going through your coil, which will determine the amount of resistance in the coil, which will impact the viability of your oscillator. To make it somewhat easy, go with 24AWG enamled magnet wire.

You now get to pick a some-what arbitrary frequency for your circuit. This I decided to go with 80KHz, it happened to be a nice middle ground between easiness and efficiency. Then you pick a capacitor value that's commonly available, I picked 150nF. This took a while to select because you need to get an inductance that is within the realm of being hand made. Using the equation:
frequency = 1/( 2 * pi * sqrt(inductance * capacitance / 2) ) (from Colpitts oscillator)
we use the capacitor and frequency values to try to get the inductance in and around 20uH to 70uH. Air-core inductors around those values are easy to make. I used a value of 53uH, which to calculate:

freq = 80k
cap = 150nF

freq = 1/(2*pi* sqrt(ind * cap/2) )

freq * 2 * pi * sqrt(ind * cap/2) = 1

ind * cap/2 = (1/ (freq * 2 * pi) )^2

ind = (1/ (freq * 2 * pi) )^2 / (cap/2)

ind = (1/ (80k * 2 * pi) )^2 / (150nF/2)

ind = 52.77uH

From here you need to use this handy inductor calculator to try to figure out what diameter and number of turns are needed. I used values of ~22 turns at 6cm diameter, with an arbitrary length around 4-5x the wire thickness for the secondary, and ~13 turns at ~15cm diameter for the primary. These values will be your STARTING POINT ONLY. You have to experiment to get it right (covered in the next couple steps).

Note that you are using the same inductance and capacitance for both the resonating coils, this is so it's easy to tune. Don't go crazy with different inductances and capacitances or else you won't get it to work.

OK, the last part of this picture is the AC to DC converter. This is what will shape the received AC into something we can use to charge a capacitor or a battery at a usable voltage. I used a CW generator here to great effect; it allowed me to tune the slave coil to produce exactly the right voltage without going over the charging voltage. I determined (through experimentation) that a two stage generator would be enough, and that will generally be fine when trying to generate ~5V. For the capacitors I arbitrarily chose 2.2uF caps, and for the diodes I chose a nice Schottky diode array with a very low 0.38V forward voltage drop. The P/N is BAS40TW-TP, however these are VERY small parts so you will probably have to order individual schottky diodes for this one. Just use ones with a low voltage drop AND a low reverse leakage current.

OK! Enough of this long-winded theory and background info, let's get to the actual good stuff!

THIS IS MY PROJECT PHOTOS
<p>hey #wwasantha i'll make this circuit but i don't get output. it is positiv and nagative supply is requaired ?</p>
<p>hi, madam</p><p>i am Mahesh , i am doing this project i have done every thing like this but no EMF is inducing in the secondary coil.</p><p>can you please help me.............</p>
hello wwasantha, sir i was working on a similar project n need a little assistance in that regard...sir i was not able to get the output..so i just wanted to know more about the coil that u have used..sir i have made a coil of 26G with the specifications on specified by u.. i.e. 26 turns on primary and 200 turns on secondary.. do i need to change this..?
agarwalprashant,dear i think u can get complete idea about it if u gone through what i uploaded. <br>MASTER COIL-24 GAGE, 26TURNS, DIAMETER 7.5cm <br> (READ MY POST IN Apr 27, 2012. 9:57 AM) <br>SLAVE COIL - 40GAGE, 150TURNS IN A 2cm x 2cm SQUARE <br> (READ MY POST IN Apr 30, 2012. 11:32 PM) <br>ABOVE TYPE OF COILS PLUS <br>WITH OTHER ALTERATION OF OSCILLATOR AND CW GENERATOR CIRCUITS I MENTION SURELY U ALSO GOT 5.5V TO 6.25V OUT PUT FROM CW GENERATOR <br>I JUST MADE SOME CHANGES OF GRIPEN'S PROJECT.BUT ALL WE GIVE THE CREDIT FOR HIM.THANKS.
sir i was working on this but then i found out that i'm not able to get any voltage across the master coil..can u guide me on this..? <br> <br>more over i hav gone thru your post and i'm working on that..i wanted to know this too.. <br>sir i'm using a a 12v adopter followed by a 7805 regulator circuit to generate 5v supply..n in the data that u hav uploded i saw 5v written on the negetive leg of the oscillator circuit..so my question is <br>is this the ground of the regulator circuit or do i have to generate -5v and connect it to this terminal?
I am also trying to develop this circuit on project board but I am unable to get any voltage across the master coil..What can I do?
sorry i just wanted to tell positive and negative supply of 5v for oscillator circuit,so you dont need generate minus 5 voltage <br>im not very good in knowledge of electronics <br>how ever select proper capacitor value with a digital multi-meter <br>149nf CAPACITORS INSTEAD OF BOTH 150nf IN OSCILLATOR <br> A 100nf CAPACITOR FROM 102nf CAPACITORS - FOR SLAVE COIL <br>AND USE 3 OF 2N2222 TRANSISTORS IN OSCILATOR <br>USE GAGE 24 FOR MASER COIL AND GAGE 40 FOR SLAVE COIL (NOT GAGE 26) <br>NICELY IT WILL WORK FOR U AS WELL <br>no magics behind that strictly follow my post to make ur project,u will win. <br> <br> <br>
sir i was working on this but then i found out that i'm not able to get any voltage across the master coil..can u guide me on this..? <br> <br>more over i hav gone thru your post and i'm working on that..see the image below question enclosed in that..!
be sure not to heat 2N2222 while u soldering them in oscillator circuit keep contact metal piece to suck heat before heat transmit to 2N2222 <br>in my case i used that safety measure and i soldered 3 of 2N2222 at last (after soldering all other component of oscillator)
sir, i'm using a breadboard to develop this circuit. i did every thing as u said but still i'm not able to get any potential across the mastercoil..:(
is there a special way to check these 2n2222 transistor....?
did u set transistor pins correctly. it is impossible to non function.coz i did it that way and succeeded.i will upload a video clip i can prove it any time.did u use 2 coils as i said in same gauges?
agarwalprashant <br>pls change capacitor which parallel y attach to slaved coil into 100pf (102pf ceramic cap) not 100uf <br>or else pf variable capacitor which using in pocket radio to select radio channels <br>
<p>please help me.............i am not getting output....</p>
Good project
<p>hi , Mr.Gripen40k , nt sure if this post is still active but i have a question . I want to power up the oscillator circuit of yours using a powerbank , would that be possible ? I'm trying to make a wireless powerbank kinda thing . Could use any advice you can provide . </p>
<p>hi can any one tell me can i charge my android HTC desire 526g..with this circuit...</p>
<p>i would like to do this project first i want to know the actual turns of master coil &amp; slave coil if the two diameters are same nearly 10 cm so please rectify my problem with your reply thank you</p>
<p>hi my requirement is like i want to transfer power minimum of 1 to 2 feet distance . so wat will be the changes I have to make. I mean accurate changes. I'm not techi student but as hoby i do some electronic projects looking at circuit diagram. So, please let me know what I have to do for my requirement or pls provide me the kit. If you are going to sell then I'm ready to buy the kit. Please let me know the price and my contact number is 9945805813 and my email address is: sjth.88@gmail.com</p>
HI GRIPEN <br>I DIDN'T HAVE AN OSCILLOSCOPE TO TUNE BOTH COILS.BUT I SUCCEEDED UR PROJECT WITH FEW EXPERIMENTATION. <br>BEFORE TELLING ABOUT THAT I NEED TO THANK U A LOT FOR UR KIND UN INTERRUPTED GUIDANCE <br> <br># I CHANGED MASTER COIL &amp; SLAVE COIL( BECAUSE <br>(1) I WANTED TO GET 5 TO 6V OUT PUT FROM CW GENERATOR FOR CHARGE MY NOKIA C6-01 <br>(2) I WANTED TO MAKE SMALLER COILS TO ARRANGE THEM IN SMALL BOXES) THESE DAYS I'M TRYING TO SLAVE COIL MAKE MORE SMALLER <br># I USED 3 OF 2N2222 TRANSISTORS IN OSCILATOR <br># I USED 149nf CAPACITORS INSTEAD OF BOTH 150nf <br> CAPACITORS ( I SELECTED 2 OF 150nf CAPACITOR WHICH ARE GIVEN149nf VALUE FOR MULTI-METER CAPACITOR TEST) <br># SAME WAY I USED A 100nf CAPACITOR FROM 102nf CAPACITORS - FOR SLAVE COIL <br> <br>I GAVE 4,92V TO OSCILLATOR THROUGH 5V REGULATOR CIRCUIT <br>( link for it-&gt; http://www.youtube.com/watch?v=CKS6zHo5T9k ) <br>I GOT 5.50V TO 6.25V OUT PUT FROM CW GENERATOR <br> <br>THIS IS THE CIRCUIT DIAGRAM I USED
Dear sir have made the circuit as per ur diagram but its not working 2.2uf is electrolitic or ceramic pls do help me awaiting positive revert from u u can mail me on my id : sbfsi1@gmail.com
Awesome, glad to hear it worked out for you :) However using an oscilloscope can allow you to tune the coils and get the maximum power transfer.
thank you gripen <br>finally i made a smaller slave coil which gives same voltage out put (5.5 to 6.25v) from CW generator <br>this simple description is about it
<p>hey it is working ? mobile charging now ?</p>
sir i hav a small questn n that is what kind of wire can we use for the coil? <br>is normal copper wire of 24G is acceptable or not..?
i'm using 26G wire n not abl to get the o/p voltage.. <br>can u help with no of turns in d coil at primery and secondary.
Ah cool, good idea with the coil form, it makes winding a lot easier.
sir i hav a small questn n that is what kind of wire can we use for the coil? <br>is normal copper wire of 24G is acceptable or not..?
Use insulated magnet wire, the guage doesn't matter because this is a low power application
why are the radii and the shape of the two inductor coils are different ??? <br>could you please explain. <br>thank you
hey dude wt about ur project does it work now?
They are different so I was able to fit them into their two containers, that's all. You can make them any size/shape you want, as long as the inductance is still the same.
hey can u help me out with a circuit by which i can transfer charge from one device to another device.i want a circuit that can absorb charge from a device.
I follow uf circuit and setup it each &amp; every point as like u.but i don't got any efficien output that the Tx portion can't made 20KHz frequency.do u use external component for its.i want to make ur circuit.pls help...
<p>@wwasantha hey guy it is working ??? charing mobile now ?</p>
<p>$4.45 DIY Wireless charging receiver + <br>transmitter solution module: </p><p>http://www.elecfreaks.com/store/wireless-charging-module-couple01-pwwcg01-p-513.html</p>
<p>$4.45 DIY Wireless charging receiver + <br>transmitter solution module: </p><p>http://www.elecfreaks.com/store/wireless-charging-module-couple01-pwwcg01-p-513.html</p>
<p>sir is there any problem is i use battery... i just notice.. my circuit is using 12vdc from a (12v 9AH)battery then i use a voltage regulator to get 5vdc.. i dont know about ur source.. this might be the problem of not having oscillation. can my battery give the required currrent? i really need help sir. <br><br>thank in advance. i really appreciate it</p>
<p>i am using L7805 voltage regulator to regulate the voltage to get 5vdc. From the spec of the voltage regulator, max output current is 1A. While for your source, u mention try at least 500mA which 0.5A, so did i pass the condition for the oscillator to work out?</p><p>i am building a wireless power transfer base on solar. so far using dc as is my priority. </p>
<p>The DC regulator won't matter too much as long as you have some caps on the output of it to provide clean power. If it oscillates too much you may be getting really weird effects in the oscillator circuit. Follow the manufacturer's recommended circuit for your regulator.</p>
<p>Hello sir<br>Great sharing. . can i ask u the type of capacitor u had used for these:<br>Primary Coil.<br>150nF capacitors ;<br>100nF capacitor</p><p>Slave coil/CW generator:<br>150nF caps<br>2.2uF caps<br><br>it is non polar capacitors right? but what kind? </p>
<p>and sir, what if i use higher voltage source for the same circuit. for example i use 12v dc source using same design.</p>
<p>You'll need to redesign the oscillator, I don't think it will work at 12V.</p>
<p>thanks a lot for the fast response sir. <br>i've try this circuit using 9v and 12v dc. i notice that the led was about to light but just for very small time. maybe split second. when i tested using the oscilloscope but i unable to get any oscillation sir. that is the problem. Is that bjt limit up to only 5 volt. <br><br>in term of redesigning sir.. any recommendation or suggestion sir. <br>and how to parallel the bjt sir. thank in advance. sir. </p>
<p>The highest I've gone on this oscillator is 6V, I'm not sure 9V would even work. Try finding a 6V source somewhere and starting with that, and you'll want to check that there is a voltage across the primary coil before you try to do anything else. Once you see AC voltage on the primary you can double-check it's the right frequency.</p>
<p>now i use a voltage regulator so that my input is 4.98v which is almost 5vdc. i build the circuit using 1 bjt only. what worry me is, how come i could get any oscillation. When i tested for ac or dc voltage across the primary coil, the value is zero. there is some problem. how to troubleshoot sir?<br><br>fyi, the inductor value of the coil is just estimation, i cant tune because no oscillation. </p>
<p>I don't think it matters what kind of cap you use. Almost everyone uses ceramic caps these days and those are widely available. They just have to be non-polarized.</p>
<p>Hello, I have a lot of problems making the coils. How can I select my resonance frequency and How do I know the dimensions of the coil??</p>

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