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 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 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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Hi, is there any recommended oscillator which produces higher voltage rating? Besides that, how will the frequency chosen in the design affects the efficiency of the system?
Thanks.
master coil 9.5*4.5....26 turne ....0.511 mm to get 5 v.
i have problem whith the diameters plz help me
The diameters/measurements don't mean as much as the overall inductance. If you follow the instructions for tuning the coils with an oscilloscope then you can easily change the diameters of the coils and still get them to oscillate at the same frequency. The total inductance is what's important.
i.) What is the max voltage and current can be transmitted from your design?
ii.) Will it be possible if I add 1 power amplifier circuit after the oscillator circuit in order to boost up the voltage to be transmitted so that I can charge up a mobile phone?
Thanks in advance. Hoping to get replies from you soon.
i) ~6V, not sure how many amps, maybe a couple hundred mA?
II) Yes, that would work, but you're probably better off designing a new oscillator
http://www.instructables.com/files/deriv/F02/JCL9/G56ZZHK9/F02JCL9G56ZZHK9.LARGE.jpg
Is just any 5V wall adapter that can source 500mA (roughly). It says that in the comments on the picture.
Could you show me your own instructable project ? (a detail one..)
step by step with all the component you've used..
creating the PCB track(transmitter, receiver etc) for your project, soldering each parts..
creating the coil, winding the wire and connect it to the each circuit board..
i'm just a beginner and actually ashame asking you for this anyway..
but i wanna make this device works for my phone..
pm please..
need fast response anyway..
thx
april 27, 2012. 9:57 AM
Apr 30, 2012. 11:32 PM
it notice where i change my project from grippen's if u study well what grippen is saying then my above 2 posts it gives everything u want
download picture post in 2 above posts i mentioned and study carefully
gud luck
(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 mean out put around 5v and 450mA from CW generator
please give me few web address which saturate my need
thanks
Be careful though! Some of the plans on the internet are a bit dangerous!
I have try out the same coil and everything the same as yours ,i manage to to get +5v as output at the slave coil. But then after i add in load(USB Fan) , the voltage drop to 0.6 V . =( any idea what just happened?
BTW your project was awesome and im hunger for it!!
Regards,
H
https://en.wikipedia.org/wiki/Voltage_regulation
In this case the circuit has really poor voltage regulation, the only way to get around it is to draw less current (don't try running a fan).
but as soon as i connected the L and C , the output Vpp (V across inductor dropped).......
As far i can guess, It cant pick up the load...
wat do u say abt it...
Now when i dont connect the LC (wid L and C inparallel) circuit, the output shows a voltage of 2.2 V (At pin 3)....
But as soon as i connect the LC , the potential at pin3 drops to 0.1V......
I m using 9V battery wid 7805 voltage reg....
now can u deduce the problem??
....
can u tell me any solution to this...??
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