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Low-Power Wireless Charging

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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 :).
 
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bobjoe12341 month ago

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??

gripen40k (author)  bobjoe12341 month ago

All of the details are explained in step 1: theory of operation, including links to inductor calculators and such.

apravin1 month ago

Hello i wanted to build a wireless charger to charge a 9V battery..... plz help me yar... thanx

arhodes184 years ago
 sorry this may be another stupid question, but what are the caps in the diode bridge section for, the 2.2 uF ones.
gripen40k (author)  arhodes184 years ago
Haha, nope, not a stupid question.

The wikipedia article does a good job explaining the CW generator, but I'll try my best to simplify it. The capacitors are a temporary storage for either the positive or negative cycle of the AC source. So when you have a negative swing, the current flows through the first diode and charges the first cap to 2.5V (in our case). Then the AC source swings positive and current flows through the first cap and second diode charging the second cap to 2.5V plus the voltage stored on the first capacitor (2.5V + 2.5V = 5V). Of course this is simplified and doesn't take losses into account, but you get the general gist.

Now I picked a fairly arbitrary value, just guessed and it worked out pretty good. If you only have 1uF ones or whatever, then those will be fine. Just try to get them roughly around the same values.
Mel007 gripen40k3 months ago
I made the circuit but the power input in my primary circuit is not the same as the power output in the primary circuit. I am attaching 5V at the input but check the flow I see that the voltage drops to 1V.
looks like there is voltage loss and as a result the led in the secondary doesn't lit up.
Do you have any suggestions.
gripen40k (author)  Mel0072 months ago
Uh, I'm not entirely sure.

The primary oscillator is a current oscillator, so measuring the voltage on the primary coil may not mean much (it won't be 5V). Could you check the values of all the components you are using, there could be a chance you're using a wrong value resistor or something.
 oh ok that makes sense...
Thanks for the help!
wwasantha1 year ago
THIS IS MY PROJECT PHOTOS
P5010927 copy.jpgP5010936 copy.jpgP5010933 copy.jpgP5010930 copy.jpgP5010939 copy.jpg
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.
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.
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..?

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?
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
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.


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..?

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
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
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
wwasantha1 year ago
HI GRIPEN
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
IMG.jpg
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 & 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...
gripen40k (author)  wwasantha1 year ago
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.
why are the radii and the shape of the two inductor coils are different ???
could you please explain.
thank you
hey dude wt about ur project does it work now?
gripen40k (author)  agarwalprashant801 year ago
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.
thank you gripen
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
IMG.jpg
sir i hav a small questn n that is what kind of wire can we use for the coil?
is normal copper wire of 24G is acceptable or not..?
i'm using 26G wire n not abl to get the o/p voltage..
can u help with no of turns in d coil at primery and secondary.
gripen40k (author)  wwasantha1 year ago
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?
is normal copper wire of 24G is acceptable or not..?
gripen40k (author)  agarwalprashant801 year ago
Use insulated magnet wire, the guage doesn't matter because this is a low power application
hii i am looking for a circuit with which i can transfer charge from one gadget to another gadget ... i can make use of the circuit designed by you to transmit charge but i need a circuit by i can absorb charge from the battery of one gadget so that i can transmit that to another gadget . can u help me please...
gnimrezt881 year ago
(From Apr 10, 2013. 10:02 PM)
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.
gripen40k (author)  gnimrezt881 year ago
No recommended oscillator, you'll have to figure that one out for yourself. The frequency effects the Q factor, which in turn effects the total efficiency. To be honest I don't have the equations anymore so again, you'll have to figure that one out for yourself :)
hi mr ...in my area we dnt use awg we just use desem which=0.1 mm so can i use slave coil 2*2 ...150 turne ...0.0799 mm

master coil 9.5*4.5....26 turne ....0.511 mm to get 5 v.
i have problem whith the diameters plz help me
gripen40k (author)  mohmed.kadora1 year ago
Hey, the AWG doesn't mean much, I just used wire that I had on hand. As long as the wire is able to handle the current you're putting through it (in my design at most a couple hundred miliamps, if that) then you should be good.

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.
gnimrezt881 year ago
Hi, I'm currently doing this for my degree project. Among all the tutorials, I find out that your's is one of the most understandable. My questions are:
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.
gripen40k (author)  gnimrezt881 year ago
Hey, well I would suggest you come up with a higher-voltage oscillator instead of using my design if you want to transfer any more power across the link. As it stands this oscillator design is cheap and easy to make, but it doesn't have too many benefits other than that :)

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
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