Introduction: Wireless Power Charger!
Runner Up in the
The Mad Science Fair
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 :)
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