Introduction: DIY Wireless Charger
In this Instructable, you will be going to know how to build your own wireless charger for any device.
Wireless power techniques mainly fall into two categories, non-radiative and radiative. In near field or non-radiative techniques, power is transferred by magnetic fields using inductive coupling between coils of wire, or by electric fields using capacitive coupling between metal electrodes. Inductive coupling is the most widely used wireless technology; its applications include charging handheld devices like phones and electric toothbrushes, RFID tags, and chargers for implantable medical devices like artificial cardiac pacemakers, or electric vehicles.
What is Inductive Coupling :
In inductive coupling (electromagnetic inductionor inductive power transfer, IPT), power is transferred between coils of wire by a magnetic field. The transmitter and receiver coils together form a transformer(see diagram). An alternating current (AC) through the transmitter coil (L1) creates an oscillating magnetic field(B) by Ampere's law. The magnetic field passes through the receiving coil (L2), where it induces an alternating EMF (voltage) by Faraday's law of induction, which creates an alternating current in the receiver.The induced alternating current may either drive the load directly, or be rectified to direct current (DC) by a rectifier in the receiver, which drives the load.
Resonant inductive coupling
According to the coupled mode theory proposed by Marin Soljačić at MIT, resonant inductive coupling(electrodynamic coupling, strongly coupled magnetic resonance) is a form of inductive coupling in which power is transferred by magnetic fields (B, green) between two resonant circuits (tuned circuits), one in the transmitter and one in the receiver (see diagram, right). Each resonant circuit consists of a coil of wire connected to a capacitor, or a self-resonant coil or other resonator with internal capacitance. The two are tuned to resonate at the same resonant frequency. The resonance between the coils can greatly increase coupling and power transfer.
IF you want to know more about the topic follow this link :
Step 1: WHAT YOU WILL NEED!!!!!!
You will need following components to begin with :
Dot PCB Board (x1)
wire 1 mm thick (7 m)
IRFZ44N MOSFET (x4)
IR2110 MOSFET driver IC (x2)
555 timer IC (x1)
CD4049 IC (X1)
10K trim pot  (x1)
10k resistor (x4)
10 OHM resistor (x4)
0.1uF capacitor  (x5)
10nf capacitor  (x1)
2.2nF capacitor  (x1)
10uF capacitor [electrolytic] (x3)
47uF capacitor [electrolytic] (x1)
47nF capacitor [polyester] (x2)
IN5819 schotky diode (x6)
Mini USB connector [male] (x1)
DC - DC 5v Buck converter
So lets start with the build.
Step 2: Winding the COILS!!?
winding a perfect spiral coil is a bit tricky.
Here is my way of winding the coil. First of all cut a small circle of diameter 1 cm with a cardboard, glue it to a piece of cardboard and make a hole in the center.
NOW, take the wire of 1 mm thickness and pass it through the hole made in the center (this is extra bit of wire for electrical connections).
Apply a lot of glue on the surface and start winding by going around the circle (glue helps in holding the winding in place). Keep on winding until number of turns becomes 30. Make 2 such types of identical coils.
Step 3: Make a Measure:
If you have a LCR meter you can skip this step. If you don't have a LCR meter , the build an inductance meter from an Arduino Uno and an op-amp (LM339). I have taken this circuit from the following website, you can find more information about this inductance meter in the website itself.( the code is also available in the website itself)
Now, measure the inductance of the coils with this meter and if you have all the conditions same as mine that is
1.0 mm thick wire, inner diameter of the coil = 1.0 cm, number of turns = 30.
you should get the inductance of the coil around 21.56 uH 26.08 uH because of unknown error.
Now after getting the inductance, you have to calculate the Resonant frequency of the LC circuit.
Given By The Formula :
F = 1 / (2*pi*sq-rt(LC))
you can use this online calculator calculate the frequency of resonance.
In my case,
L = 26.08 uH and C = 47 nF
which gives the resonant frequency of F = 143.75 Khz.
now, we have to build the oscillator circuit, whose oscillation is of the frequency 143.75 Khz.
Step 4: The Oscillator Circuit...
There are lots of way of making an oscillator circuit . In this circuit we will use a 555 timer IC to produce a signal of 143.75 Khz but its not enough to drive the LC circuit(transmitter coil with capacitor in series). so we have to build a H bridge mosfet driver circuit to drive the LC circuit.
With reference to the circuit on the above website and some minor changes I have made a circuit to drive the LC circuit.
Just follow the circuit that I have attached here.
The 555 timer IC in Astable Multivibrator with 50% duty cycle produces the required oscillating signal which is fed to the IR2110 IC.
The full H bridge Mosfet driver circuit to will output sine wave when the inputs A=D and B=C and B(C) is Inverted state of A(D). So an Inverter IC (4049) is used to achieve this.
This oscillating Voltage creates a sinusoidal current through the transmitter coil which induces magnetic field around it.
when the receiver coil in parallel with a capacitor, whose resonant frequency as same as that of the transmitter coil is placed in its magnetic field current is induced.
This induced current is converted to dc using bridge rectifier and regulated to 5 V DC to charge the mobile using a buck converter.
Step 5: #Final Measure:
Now, after building all the circuits according to the schematic check everything and also measure everything.
again if you have any device to measure frequency then its okay, if not just upload the following codeto Arduino Uno.
web address : https://forum.arduino.cc/index.php?topic=324796.0...
Measure the frequency at 3rd pin of the 555 timer IC.
while measuring the frequency adjust the 10K trim pot to get the required frequency (i.e, 143.75 Khz).
now take a multi meter measure the following parameters:
Input Voltage[ Vin ](i.e, check whether it is exactly 12 V or not).
Input Current[ Iin](i.e, current to the circuit from 12 v power supply).
Output Voltage[ Vout ](i.e, check whether it is exactly 5 V or not).
Output Current[ Iout ] (i.e, current to the mobile from buck converter).
Pin = Vin * Iin
Pout = Vout * Iout
Efficiency(n) = Pout / Pin
My readings : Vin = 11.8 V ; Iin = 310 mA ; Vout = 5.1 V ; Vin = 290 mA
which gives efficiency of 40.4%
Step 6: #The Enclosure.
I have recycled an old mobile box as the enclosure as you can see in the image.
once you have done, you can charge mobile or any device that requires 5 volts, the charging current is 300 mA.
(which is bit slow for mobiles). The output power can be increase further but the efficiency will decrease.
As you can see I have connected a mini USB connector at the output of the buck converter. This can be connected to any device and can be charged wirelessly.
Step 7: Moment of Truth!!!!
WHY SO INEFFICIENT :
As you can notice the efficiency of this is very low, but why? It is due to poor air coupling, skin effect and error in inductance of the hand winded coil and the frequency of the oscillator circuit itself is not stable.
so how do we overcome these problems??? well we can utilize special type of wire called LITZ WIRE to over come skin effect. The effect by which the current passes only through a certain depth of the conductor at high frequency is known as skin effect. We can also use Ferrite base to increase inductance and increase the coupling of two coils effectively. Of course there are many coils in online shops with the above requirements which can be used to increase the efficiency of the wireless charger.
If you want to build this for demonstration purposes the above coils are enough. But, If you want to use this for any daily purposes I suggest you to buy one online.
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