Wireless Power Charger!




Introduction: Wireless Power Charger!

About: I'm 21, and I have a profound interest in electronics, lasers and Geology.

Wirelessly power your iDevices!

Wow, I'm really surprised at how many views this is getting! Thank you everyone for reading!

I recently made a boost converter (for those unfamiliar with them, they effectively boost the voltage up to a useable amount) to make a USB Ipod charger using 2 AA batteries.

Now that that was done and over, tested tried and true, I decided I wanted to make something a little more snazzy!



Behold, the wireless ipod charger!

Uses all 12 volts of 6 (2 in parallel for each cell) lithium batteries!

Draws under 3 amps all the time!

Perfect for kids parties!

Now in 5 new flavors!

I've searched around on this website, and noticed that almost all of the instructables on here with wireless power seem to lack a proper explanation about how to build one; Or, when they did build one, they used an inefficient method of doing so...

This transmitter works fantastic, and can run on pretty much any voltage above 12 volts, and below 24! It's also extremely efficient (little power lost) and, it generates almost no interference. (one wireless power instructable used a square wave in the primary; Square waves have a lot of harmonics, and can cause havoc on computer systems, radios, and other sensitive electronics)

I've come to solve all of these problems!

Step 1: So You Want to Make It, Right?

You'll need some parts.

2 MOSFETS - I understand that this is a rather vague statement. You can use the IRFP250, if you want to. However, the lower the on-state resistance is, the less heat will be generated. You can get these from any ol electronics supplier. Farnell, mouser, digikey, ebay

2 10k ohm resistors. (brown black orange) You can use 1/4 watt ones. Again, you can get these at the listed ones above, and even radioshack should have these.

2 Ultrafast Diodes - They need to be above 400 volts. I used UF4007's. Farnell, Mouser, Digikey, ebay...

2 Twelve volt zener diodes - Nothing special to say here! Again, Farnell, Mouser, and Digikey.

1 7805 - I know I said I used a boost converter. However, a boost converter is a whole another instructable, and I can't explain how to build one in this. So, for now, we'll just use a 7805. Radioshack has these in addition to the places listed before!

2 18k ohm resistors - 1/4 watt (brown - gray - orange) Radioshack, and the listed places.

2 12k ohm resistors - 1/4 watt (brown - red - orange) " "

1 Ferrite toroid - it can be around 1/2 inch in diameter. Wind roughly 30 turns of enameled wire on it, and you'll be set! You can get these from old Tube televisions scrapped, ATX PSU's. Basically anything you can take apart *should* have one of these.

USB Female Port - I scavenged mine from an old adapter PCI board we had from 2000. We didn't need it, so I figured why not? If you don't know where to get one, you should be able to get them from Mouser, Digikey, Farnell, and ebay.

Two sets of tank capacitors - I used 4 1 uF capacitors for mine. You can use two 2 uF capacitors instead, if you want to. You NEED to make sure they're MKP, or a better type! Polyester ones, electrolytics, anything along those lines will not work, and will overheat! WIMA makes some nice capacitors that work fantastic for this project. You can alternatively use Farnell, Digikey, or Mouser to find some MKP capacitors to use. Ebay will have some too.

You'll also need some 14 gauge wire, and tape!

Step 2: The Schematic

To build it, just follow the schematic as shown. (If you need help, please, do not hesitate to message me!)

If you're having trouble identifying the MOSFET's pins, look up the part number of the MOSFET you're using, and follow what it says on there.

For those following it to the book, the IRFP250's pin out goes like this, from left to right; Gate, Drain, and then Source.

Make sure when you're making this, the diodes are put in the correct way. Don't mix up your zeners with your regular ones!

If you mess this up, your MOSFETs will almost certainly go boom!

You could use a SMPS laptop cord to power it, which puts out around 18 volts. (if you do decide to go this route, make sure your power supply can handle a good amount of current draw. Mine is rated at 3.5 amps, and occasionally the OC (overcurrent) detection will trip!)

I will add a word of warning; If you plan on just using a 7805, you must NOT exceed 15 volts input, on the transmitter. Due to resonant rise, the capacitor will charge over what the 7805 is capable of handling. Be careful please!

If you want to put more juice in your transmitter, you must use a buck converter, otherwise things will be very unhappy on your receiving end.

For the diodes, the black band on it, or the white band on the UF4007's indicates the cathode. The other end is the anode. (for simpler terms, the cathode is the pointy end of the diode symbol, where the line goes across it. The anode is the flat base of the triangle)

Mind you, this is just for the transmitter!

Changing the inductor value will change the amount of current draw. A smaller value inductor will equal more current, a larger value one, less current. I've gotten it all the way down to 1.5 amps max draw, but the inductor overheated! (the wire gauge was too small)

Changing the coil turns will ALSO additionally change the current draw, as well as the frequency. More turns, lower frequency, lower current. (I believe, this is a result of the resistance of the wire, and the frequency change)

Also note; the higher the input voltage, the more distance, you should get out of your transmitter. As an additional bonus, you will also receive more voltage at the receiving end as well! Remember, though, at this comes a cost; the mosfets will get warmer, and your current draw will increase!

Step 3: Making the Coils

I understand that making the coil wasn't explained at all, and I figured it deserved its own step!

To make the coil for the transmitter, take your 14 gauge wire, and get around 7 - 9 feet of the stuff off your source. Take this, and find the middle point of the wire; cut here, with a pair of wire cutters. (or, if you're good at stripping, you can try to take the jacket of the wire off, without cutting the conductor inside) Strip around 1 inch of wire off of all of the ends, so you have nice shiny copper glaring back at you.

Then, get some masking tape, and wind it around two parts of the coil. This makes sure that nothing gets out of place when you're getting the rest of the tape on! Once you have that bit done, just wrap the coil as you see fit!

And there, you have your coil done!

To make the receiving coil, basically repeat the process; Just leave out the center tap part.

Step 4: Receiving...

The receiving end is less complex. Make sure you use the same capacitor value, as well as following the USB pinout as I have written in the schematic.

You can try and experiment with different turns ratio's of the coils and see what kind of performances you get! This has to do with resonance, and step-up / step-down ratios.

Try adding more voltage, and see if you get more distance; another way of possibly increasing distance is to increase the resonant frequency a bit. Increasing the frequency should give you more distance, with additional current draw.

To increase the frequency, just lower the capacitor values. Personally, the lowest I'd go would be around 1 uF. Make sure when you lower the cap value, you do it for both the receiving, and the transmitting ends!

Also, remember, the idea does not have to apply only to USB. I've noticed that due to resonant rise, the filter capacitor charges to the peak of the output sine wave....

At 12 volts into the transmitter, I was getting around 24 volts at the receiver end! (this isn't the effective voltage however; once you put a load on it, it drops a bit) At 15 volts in, I was getting 35 volts on the receiver! (wow, that's quite a bit of a jump, huh?)

This means that you should be able to power other things as well. Use whatever your mind comes to!

Step 5: Thoughts, and Explanation

The ZVS driver is used for a lot of things due to it's simplicity. Your laptop might be using the same oscillator format to run its backlights!

However, in this case, the reason it works is because the ZVS driver begins by oscillating at around 50 - 60 khz. We can't hear it since it's above our hearing range.

Resonance can be thought of like a Pendulum. If you hit a pendulum, it will move forward, and then back. If you hit the pendulum again, right as it starts to swing downwards, the pendulum will travel faster and higher than before. It's very much the same in electronics, just instead of speed and height, it's voltage and current! You can observe it pretty easily with a cup of water. If you shake it just the right way back and forth the water will spill right out of the cup, due to resonance.

Due to this magic called resonance, the voltage swings in the tank (between the 3 + 3 coil and the 2 uF capacitor) are much higher than what the input voltage is. Resonance helps with transmission distance, and also, as a result of how the MOSFETS turn on, they're in what's called Zero Voltage Switching, where they turn on and off when the voltage across them is zero. (meaning, they generate little/no heat due to switching losses). However, due to on-state resistance, they still make a little bit of heat.

ANYWAY, going away from the complicated bits of it, the reason it can transmit power is caused by magnetism. As the coil oscillates, it sends an alternating magnetic field through the air, which is picked up by the receiving coil (and again, due to resonance, the voltage rises upwards!) and thus, power is transmitted through air! The same basic concept is behind radio waves; though, amplifiers are needed to get the audio out of the air, and the frequency is much higher!

I made all of the pictures shown in, though, the transmitter picture is a modified version of the famous Mazzilli flyback driver. (a great, versatile circuit... Used for so much, thanks Vladmiro Mazzilli for this!)

And, one more thing; In another instructable, once I get some protoboard, I'll explain how to make a buck converter. It's relatively easy, and requires just a few parts.

And as a safety note; I'm not responsible for any "oopsies" you make if you decide to construct this circuit. You NEED to make sure everything is connected properly!

If I do somehow end up winning the Epilog contest, I would use the laser etcher to first and foremost, make PCB's. I don't like the traditional way of etching (with chemicals and nasty fumes) and plus, I could additionally sell the PCB's to other electronics enthusiasts for smaller amounts of money, than most etching companies make you pay. I'll try my best to bring this hobby back into the spotlight!

Thanks for reading, and please rate, and vote :)

The Mad Science Fair

Runner Up in the
The Mad Science Fair

4th Epilog Challenge

Participated in the
4th Epilog Challenge

3 People Made This Project!


  • Remote Control Contest

    Remote Control Contest
  • First Time Author Contest

    First Time Author Contest
  • Build a Tool Contest

    Build a Tool Contest



10 years ago on Step 4

Hey this is a great Ible! But I cannot read this section. BTW these are the Resistors in the sender schematic.


Reply 10 years ago on Step 4

You gotta click on the little [i] and then the link to the original image link:


It's 18k and 18k on the top side, and 12k and 12k on the bottom side ;-)


Question 9 months ago on Step 5

Hello, for making the receiving coil could be only 3cm diameter, should the amount of wire used, be the same?


Question 4 years ago

Can i know the schematic for voltage regulator?


4 years ago

Hello! Can this be used to charge a laptop? Or a kitchen device? I am thinking to use this on my new house for certain areas were we do not have that many wires!


5 years ago

I wonder if I can put this on my motorcycle luggage rack for the brake lights. So far, the only commercial solution is to hardwire the luggage rack but I often remove it when not in use. There had been no one yet who have thought of making one like this so it looks like I have to make one myself. Thanks for the idea.


5 years ago

Hi there,

I made this circuit and I noticed that the coils become really hot when the circuit is on.Is that normal?


5 years ago

Hey guy. I'm very excited to do your project. But I have one question: if the ipod can recharge with 5V, that recharger can be "universal"?
Thanks man, your project is so amazing.


5 years ago

What is this black thing on the receiving end?


5 years ago

Awesome project! In the process of trying to construct it....Can you explain what the 1000-3000 uF capacitor on the receiving end is for though? - I don't think I saw that one on the parts list... Can that be any capacitor type, or does that need to be MKP too?


6 years ago

hey, would you mind sending me more detailed pictures of the build. I'm near at building with schematics and can't really follow it that well. Thanks alberteinstine2012@gmail.com


6 years ago

Hi. Could you tell me please how much energy is wasted from the batteries when transmitting power wirelessly?


6 years ago

what should be the diameter of coil


Reply 6 years ago

D = 6.7infor the 7ft wire

D = 8.594in for the 9ft wire

Disclaimer: If you read further please note that no part of the explanation below is written with the intent to insult anyone's intelligence but rather is aimed at being complete. It does this by not assuming that the reader intuitively knows anything about mathematics whatsoever.

Summary equation:

D = 2 x[[ (Length of wire) / (# of turns) ]x[1/(2Π) ] ]

Derivation of Diameter D equation above:

If you know the total length of the wire L= whatever length you want

length of wire in ft * 12 = length of wire in inches I will call L


c =
number of turns

plug c into:

r =

plug r into:

D= 2r

Conceptual explanation:

Notice that the length of the wire should be from 7 to 9 feet.

Reveals that coil is wound three times completely and a fourth time including the open ends.

For sake of convenience let's turn feet to inches: 7ft *(12in for every 1 ft) = 84in
or if you want 9ft instead: 9ft *(12in for every 1 ft) = 108in

Since the coil is wound three times completely and a fourth time with open ends we can approximate that the coil is wound 4 times completely.

Now you want to take the length of the wire and divide it by the number of turns it will give you the circumference of the single circle about which all 4 turns are wound.

For 7ft having been converted to 84in we take 84in/4 turns= 21in
circumference (which I will call c) of the circle with the 7ft long wire is = 21in
c = 21in
and if you choose to go with the 9ft long wire instead:
9ft converted to 84in take 108in/4 turns= 27in
c = 27in

Now that we have the circumference, we can acquire the diameter.
You may recall from one of your classes that the circumference of the circle is "2Πr" if you didn't- now you do. Also recall that I have said above that the letter c is set equal to the circumference ( c = 21in or c = 27in ), knowing this we can use the identity of circumference to find the radius:

Let's start with using c = 21in.

know thatc = 21in but also c = 2Πr. Now pretty much anyone can see that 1 = 1 or 2 = 2. Likewise c = c thus:

21in = r

I am hoping you know that the diameter is twice the radius because that's where I got this relation:

D =2r where D is the diameter of a circle and r is the radius.

Divide 21 by 2Π to acquire r.

For the 7ft (or 84in long) wire the radius of the coil is:

r =21in = 3.34225380493in rounding r ≈ 3.342

Now multiply by two to derive the diameter:

D =2r => D = 2(3.342) => D =6.684 ≈ 6.7in for the 7ft wire.

Therefore the diameter is given by:

For the 9ft (or 108in long) wire the radius of the coil is:

r = 27in = 4.29718346348in rounding r ≈ 4.297

Therefore the diameter is given by:

D =2r => D = 2(4.297) => D = 8.594 ≈ 8.594in for the 9ft wire


6 years ago

Thanks a lot!!

I was looking for a long long time something like this!

Can you help me ?? .... In the ferrite toroid we have to wind with 30 turns but I dont know what kind of gauge wire use.
Anybody can help me?


6 years ago

Thanks so much for this AWESOME instructable, after much headache I
am able to say that I was finally able to get things working. And I'm
an absolute beginner so that goes a lot to say about the writer, thank

I did run into a slight issue though and was hoping I
could get some guidance, granted I havent built in the connection to the
7805 and have the tx built as well as the receiver built (caps and
rectifier), when I go to measure the dc current at the rectifier I only
get .08 on my multimeter... I do however get a full 12 volts at the tx
though... Any thoughts?

Hooked up to 12v 1.8 amp power,
everything is identical to instructable (it works, just low low low
voltage at receiver end). Only think i notice may be different is that
my inductor is made with 26 gauge magnet wire (30 turns) when it looks
like in yours you are using some thicker gauge wire.

Am i just
jumping the gun and needing to connect all the way through the 7805 in
order to see the full 5 volts? I just didnt want to solder the thing
until all tested, figured i would at least get 5v at the rectifier..
unless i'm reading my multimeter wrong (at 20v setting reads .08 max).

Thanks for any help!


6 years ago on Step 5

Can I use the powermat receivers like they have at starbucks instead of building it? You can get those for free from the powermat website and saves building that part myself. Will the transmitter work for those?

Nishant Lovea

why do we require such a high frequency of operation? and what is the diameter of the turns of primary and secondary transmitter?

Nishant Lovea

how will the mosfets get triggered?and what is the operating frequency?and y do we need a high frequency of operation?