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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 :).
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 :).
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Signing UpStep 1Theory 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 value 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.
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!
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 value 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.
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!
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(2) i couldn't found BAS40TW-TP schottkey diode from sri lanka,please give me some examples that meet ur requirements
(digikey for ones with Vf<400mV@1A and Ir<1mA@20V)
(3) i found IN 4007,IN5819 ,SR360 which one is best for CW generator
thanks!
2) Use whatever schottkey diode you can find, as long as it has a low forward voltage it will be fine.
3) Use whatever general purpose components you can find, this circuit doesn't care too much.
I DIDN'T HAVE AN OSCILLOSCOPE TO TUNE BOTH COILS.BUT I SUCCEEDED UR PROJECT WITH FEW EXPERIMENTATION.
BEFORE TELLING ABOUT THAT I NEED TO THANK U A LOT FOR UR KIND UN INTERRUPTED GUIDANCE
# I CHANGED MASTER COIL & SLAVE COIL( BECAUSE
(1) I WANTED TO GET 5 TO 6V OUT PUT FROM CW GENERATOR FOR CHARGE MY NOKIA C6-01
(2) I WANTED TO MAKE SMALLER COILS TO ARRANGE THEM IN SMALL BOXES) THESE DAYS I'M TRYING TO SLAVE COIL MAKE MORE SMALLER
# I USED 3 OF 2N2222 TRANSISTORS IN OSCILATOR
# I USED 149nf CAPACITORS INSTEAD OF BOTH 150nf
CAPACITORS ( I SELECTED 2 OF 150nf CAPACITOR WHICH ARE GIVEN149nf VALUE FOR MULTI-METER CAPACITOR TEST)
# SAME WAY I USED A 100nf CAPACITOR FROM 102nf CAPACITORS - FOR SLAVE COIL
I GAVE 4,92V TO OSCILLATOR THROUGH 5V REGULATOR CIRCUIT
( link for it-> http://www.youtube.com/watch?v=CKS6zHo5T9k )
I GOT 5.50V TO 6.25V OUT PUT FROM CW GENERATOR
THIS IS THE CIRCUIT DIAGRAM I USED
could you please explain.
thank you
finally i made a smaller slave coil which gives same voltage out put (5.5 to 6.25v) from CW generator
this simple description is about it
is normal copper wire of 24G is acceptable or not..?
is normal copper wire of 24G is acceptable or not..?
can u help with no of turns in d coil at primery and secondary.
MASTER COIL-24 GAGE, 26TURNS, DIAMETER 7.5cm
(READ MY POST IN Apr 27, 2012. 9:57 AM)
SLAVE COIL - 40GAGE, 150TURNS IN A 2cm x 2cm SQUARE
(READ MY POST IN Apr 30, 2012. 11:32 PM)
ABOVE TYPE OF COILS PLUS
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
I JUST MADE SOME CHANGES OF GRIPEN'S PROJECT.BUT ALL WE GIVE THE CREDIT FOR HIM.THANKS.
more over i hav gone thru your post and i'm working on that..i wanted to know this too..
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
is this the ground of the regulator circuit or do i have to generate -5v and connect it to this terminal?
im not very good in knowledge of electronics
how ever select proper capacitor value with a digital multi-meter
149nf CAPACITORS INSTEAD OF BOTH 150nf IN OSCILLATOR
A 100nf CAPACITOR FROM 102nf CAPACITORS - FOR SLAVE COIL
AND USE 3 OF 2N2222 TRANSISTORS IN OSCILATOR
USE GAGE 24 FOR MASER COIL AND GAGE 40 FOR SLAVE COIL (NOT GAGE 26)
NICELY IT WILL WORK FOR U AS WELL
no magics behind that strictly follow my post to make ur project,u will win.
more over i hav gone thru your post and i'm working on that..see the image below question enclosed in that..!
in my case i used that safety measure and i soldered 3 of 2N2222 at last (after soldering all other component of oscillator)
pls change capacitor which parallel y attach to slaved coil into 100pf (102pf ceramic cap) not 100uf
or else pf variable capacitor which using in pocket radio to select radio channels
THANKS A LOT !!!
http://en.wikipedia.org/wiki/Reed_switch
Otherwise you could look for... increased current consumption on the master power supply, or the peak voltage decrease on the master coil (but that can be effected by other means and is hard to test).
I USED ALL COMPONENT AS U GIVEN IN UR NOTE.I HAD MADE 2 COIL CLEANLY BUT RECIEVER IS NOT PRODUCE A CURRENTMORE THAN 0.013V WHY THIS HAPPEN TO ME PLS HELP
THANKS