The power cord, I know you hate it. Sometimes, you just want to cut it apart! Well say goodbye to your power cords, because with the power of inductive coupling your device will not need to be connected metal to metal. Seemlessly your device can be charged!
This instructable will show you the basics of creating your own cheap and easy wireless power mat, which you can use to power your device through the air!
New Update: complete list of components.
Check out my new project on sending a balloon into space!!
Step 1: What Is It? How Does It Work?
A few years ago MIT created a system for transferring power wirelessly. They transmitted power over a two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Back in 2006, this was a pretty cool thing. You can only imagine what the implications of something like this would be. Well, unlike most of us, we do not have the time or material goods like MIT has. So i have made this simple and easy to follow Instructable, so all of you good people can experience the joy of wireless power.
Inductive Coupling uses magnetic fields to transfer power. There is a primary coil, which generates a magnetic field. Then there is another secondary coil which is composed of a capacitor and a coil, the capacitor creates a resonant circuit with the primary and secondary coils. Seem easy? Well, before publishing this instructable I found many useful and a lot of non-useful info on the subject.
In my research I found, that to transfer power in very complicated. Once i did it I found that you do not need to go to MIT do do this sort of stuff. With a little electrical know how, this is easy.
It all starts with the transmitter. This transmitter needs to create 147.7 kHz square wave AC signal. Let me take a minute to explain this all. Level one on the frequency scale is Hertzs, then there is kHz, then MHz. MIT used a 10 mHz wave to drive there coils, but for this we will be using a 147.7 kHz signal so it does not get too complicated.
The secondary coil has a 0.02 uF capacitor. This will allow the two circuits to be coupled therefore, transferring power efficiently. The 0.02 uF capacitor is used only for this frequency, and the value of this capcitor will change depending on the frequency.
The primary coil creates a magnetic field, when another coil is placed near it, energy will be induced into it.
Be in mind that i could not get a hold of a 0.02uF capacitor so i used two 0.01uF capacitors connected together.
Step 2: Creating the Primary Coil
The primary coil uses magnet wire, which is easy to get at RadioShack. http://www.radioshack.com/product/index.jsp?productId=2036277
We will use magnet wire as the material for our coils.
Next we need something to create the 147.7 square wave AC signal. I saw videos on youtube like this one. http://www.youtube.com/watch?v=SSgo_N-5JOg Which uses a function generator. Sadly, these cost a lot of money, so i wanted to get a low cost one, that still did the same thing, just not as high of a frequency. This http://www.sparkfun.com/commerce/product_info.php?products_id=9002 is great for what i needed. Cheap and simple.
This will be the main board to create the signal.
By using a pencil or nails on a 2 x4 and your magnet wire, you can make a pretty good coil. I did about 30-40 turns, depending on the thickness of your magnet wire. Magnet wire has a very thin coating on the top of it. To get this off you can light a match and put the magnet wire in the flame for a few seconds. Take the two ends of you coil and put it into the function generator on the top two screw terminals, one in each terminal. Polarity is not a problem right now because the signal will be AC. Now place your 0.02 uF film capacitor in parallel with the terminals you put the wire magnet ends into. Turn the function generator on and use your multimetter to get it to somewhere near 147-149 kHz by turning the potentiometers. Make sure the switch on the left of the board is set to square, and your good to go. The top to terminals will allow for an AC signal.
Step 3: The Secondary Coil
This circuit is one of the simplest you can ever create. It is composed of magnet wire coil but smaller like the primary, a 0.02uF
capacitor also like the primary, and some leads you can attach things to. For LED's the circuit looks like that. Yet, for powering your iPod and other devices that use DC power you need a diode bridge, or rectifier which can turn AC into DC to power your portable device. Take a look for yourself that the secondary coil has an AC output which will only power LED's.
Step 4: Testing Wireless Power Through Different Materials
Yes, I decided to go a little further because of the response that I received.
You were always told as a kid, water and electricity DO NOT MIX, and that may be true, but not with wireless power. I tested this in water. No, I did not get shocked, but you may. NO! You will not I promise. This Step shows that this type of wireless power can pass through almost anything, except metal, I know, I was sad when i found that out. I mean, for a practical use, many people have desks made of metal where the coil is. This is not good, but I digress, we must move on.
Water! I mean who would think that this kind of technology has this kind of potential! It works that same exact way as if it was not in water. It is in a plastic bag as you can see. Only to protect the electronics. Unlike WiFi which is can be weakend by walls and other things, Wireless Power is not!
Step 5: Circuits
These three pictures I have posted are of the circuits that I used. I have also posted a third picture of a theoretical circuit (has not been tested so i am not sure if it works) which turns the received energy into DC so you can hook it up to your favorite electronic device, iPod, cell phone...
Primary Coil-The function generator is the Main circuit of the primary, but you can easily buy it from the link posted earlier. Alon with the magnet coil.
In the Secondary Coil Diagram, the only capacitor is a 0.02 uF as I explained why.
Step 6: Data
The power coming directly from the function generator to the coil: 110.5 mW.
Maximum power efficiency achieved is 42.2%. This is a very respectable power efficiency considering a limited budget and short experimentation time period.
The following chart is a visual representation of the above data points.
The following graph represents how the power output of the secondary coil was effected by efficiency at certain distances from the primary. At three inches, the current technology outputs a value that is very minute and is not efficient enough to power much of anything. However, at zero inches, the power output is very capable of achieving the goal in the engineering objectives.
Step 7: Extra Hardware
I have now added a AC to DC diode bridge which converts AC to DC. Then i added a Joule Theif to the diode bridge, which is a very simple circuit that can amplify input power (the Dc voltage from the diode bridge). http://www.youtube.com/watch?v=gTAqGKt64WM
This allows the LED to be lit when its father away from the coil, because the voltage going to the LED is higher. It is now able to power DC devices.
Step 8: Extra Information
I have shown you the basics of transmitting power wirelessly over short distance. Now it's your turn to make your own and comment on how your made your Mat and what you used it to power.
-If you have access to a larger function generator you can use that in the same way we used here.
-Then you can also use the 555 timer, which can create the same kind of signal, but is a bit more complicated.
-So for all of the comments, here's some more info about about how this system functions.
With my size coils as seen in these pictures, based on how well you can tune the frequency, your looking at an efficiency range of about 70 to 85%. The led in the secondary coil, starts to fade when it is about 2 inches away from the primary. At about five inches, it is pretty well dark, but at four inches it is still a bit lit. If the coil is turned vertical, the led is dark. Please comment if you know why it is not bright when the receiving coil is vertical.
-Here's some variables that may change the outcome:
Wire gauge - 22
Amount of Wire - 40 feet
Capacitor value in primary and secondary - 0.02 uF
input voltage - around six volts; hint; i used a irf520 mosfet to amplify the power input from the function generator, which increase the secondary voltage tremendously. I'l post some pics soon.
usage of secondary coil - a voltage meter should be used first to see if there is any voltage; then you can attach an LED. I've gotten 5v from the secondary with my circuit from a 6.3 input voltage to the primary
Step 9: List of Components
Plastic Project Box
IRF510 or IRF520 MOSFET
0.02µF capacitor x2
Magnet Wire (Gold for Primary, Red for Secondary)
Wall Power Converter 9-18VDC
_Boltz_ made it!