A wireless cellphone battery charger is a device that charges a compatible cellphone or mobile phone placed close to it, through high frequency wireless current transfer, without any physical contact.
In this post I have explained how to build a wireless cellphone battery charger circuit for facilitating a cordless cellphone charging without employing a conventional charger.
The Objective
Here the cellphone is required to be installed with a receiver circuit module internally and connected to the charging socket pins, for implementing the wireless charging process.Once this is done, the cellphone simply needs to be kept over the wireless charger unit for initiating the proposed wireless charging.
In one of our earlier posts I have explained a similar concept which explained the charging of a Li-ion battery through a wireless mode, here too we employ a similar technique but try to implement the same without removing the battery from the cellphone.
Also, in our previous post I will comprehensively explained the basics of wireless charging, we'll take the help of the instructions presented there and try to design the proposed wireless cellphone charger circuit.
We'll begin with the power transmitter circuit which is the base unit and is supposed to be attached with the mains supply and for radiating the power to the cellphone module.
The Transmitter (Tx) Coil Specifications:
The transmitter circuit for this wireless cellphone battery charger is the crucial stage and must be built accurately, and it must be structured as per the popular Tesla's pancake coil arrangement as shown below:
Making a PCB version of the above Pancake coil.
Inspired from the above theory, the smaller layout of the same coil can be etched over a PCB as shown in the following diagram, and wired as indicated:
Dimensions: 10 inches by 10 inches, bigger size might enable faster charging and better current output
The figure above shows the power emitter or radiator design, also recall the circuit diagram from our previous post, the above design utilizes exactly the same circuit layout, although here we do it through a PCB by etching the winding layout over it.
A careful observation shows that the above layout has a pair of parallel coiled copper tracks running spirally, and forming the two halves of the transmitter coil, wherein the center tap is acquired with the aid of the linked red jumper wire across the ends of the coils.
The layout allows the design to be compact and effective for the required operations.
The track layout could be in the form of a square, or oval on one side and squarish on the other in order to make the unit even sleeker.
Rest of the portion is quite straightforward and is as per our earlier diagram, where the transistor is 2N2222 included for inducing the required high frequency oscillations and propagation.
The circuit is operated from a 12V/1.5 amp source, and the number of turns (coils) may selected approximately in accordance with the supply voltage value, that is around 15 to 20 turns for each halves of the transmitter coil. Higher turns will result in lower current and boosted voltage radiations and vice versa
When switched ON, the circuit may be expected to generate a strong magnetic flux around the coiled tracked, equivalent to the input power.
Now the radiated power needs to be absorbed using an identical circuit for executing the wireless power transfer and the intended cell phone charging.
For this we need a power collector or receiver circuit for collecting the radiated power, this may be devised as explained in the following section:
Dimension: 3 inches by 3 inches or as per the accommodation space available inside your cellphone
As may be witnessed in the above receiver design, an identical layout of the coil may seen, except that here the two concentric spirals are connected in parallel to add current in contrast to the transmitter layout which incorporated a series connection owing to the center tap restriction for the design.
The design is supposed to be small enough to fit inside a standard cellphone, just below the hind cover, and the output which is terminated through a diode may be connected either with the battery directly or across the charging socket pins (internally).
Once the above mobile battery charger circuits are built, the transmitter circuit may be connected with the indicated DC input, and the receiver module placed right over the transmitter board, at the center.
An LED with a 1k resistor could be included at the output of the receiver circuit in order to get a instant indication of the wireless power conduction process.
After the operation is confirmed, the output from the receiver may be connected to the socket of the cell phone for checking the response of the wireless charging effect.
However before this you may want to confirm the output to the cellphone from the wireless receiver module...it should be around 5 to 6V, if it's more, the black wire could be simply shifted and soldered a few coils towards the top until the right voltage is achieved.
Once all the confirmation are complete the module could be accommodated inside a cellphone and the connections done appropriately.
Finally, hopefully if everything is done correctly the assembly might allow you to keep the cellphone directly over the transmitter set up and enable the proposed wireless cellphone charging to happen successfully.
Making a Practical Prototype
The above wireless power transfer concept was successfully tried and tested with some modifications, by Mr. Narottam Gupta who is an an avid follower of this blog.
The modified wireless cellphone charger circuit and the prototype images can be witnessed below:
Sir I have to discuss about 24 volt induction.
Hi Swagatam, I hope you are well.
I wanted to ask you if it seems possible to make a 42V – 2A wireless charger for an electric scooter with a designer circuit.
Thanks a lot in advance
Hi Juan,
I may be possible to build it if you are able to optimize the resonance frequency of the circuit correctly.
If we can calculate the frequency and the resonance components of the circuit correctly then it will be successful.
Hi Sir. I just want to ask how do you trigger the coil? I didn’t understand the working principle. Why didn’t you switch the Tx coil?
Hi Halil, the coil is triggered and oscillated by the transistor through a feedback mechanism.
I am a student, what you did is almost the same as what I did. My project is about a table that charges a laptop wirelessly.
Can you do a simulation for my project like what you did on this page? Because I don’t know how to do a simulation.
Sorry, I am also not good with simulations, so it might not be possible for me, by the way I cannot see any simulation done in the above article…
Hello.I want to design the pcb file of this circuit..but I need calculations for board thickness.track thickness.distance between tracks and number of coils..please guide me Wireless Cellphone Battery Charger Circuit
Hi, Sorry, I do not have the exact dimensions of the board, it was designed as per my imaginations and assumptions. You will have to consult a professional PCB designer for getting the exact size and thickness. Track thickness can be 1.5 mm.
Sir on the top there you said in the transmitter coil(Rx) more turns result in higher voltage lower current while less turns result in lower voltage higher current right please correct me if I’m mistaken. It may be the reason why my power bank was unable to charge my phone maybe doe to higher voltage and lower current
I meant the transmitter coil (Tx).
Hi Sadiq, yes that’s correct. However the transmitter turns must be properly calculated with regards to the input supply voltage and must not be too less. The same is true for the secondary winding.
Pls sir what’s the diameter of the reciever coil
You can use any thin enameled copper wire, for example which are used in 1 amp transformer secondary side. Can be 0.3 mm diameter
Ok sir.so how about the coil inductance calculation and the matching resonance frequency calculation
Resonance has not been applied in the above circuits.
Pls sir why’s the transmitter coil thicker than the reciever coil and how can I calculate the coil inductance for both the transmitter and receiver and also the matching resonance frequency
Hi Melvis, it is because the receiver coil has more number of turns than the transmitter so that it can absorb maximum wireless transmission from the transmitter coil. Transmitter needs less number of turns in order to match with the transmitter frequency and to enable high current output. However, the receiver coil can also have the same number of turns as the transmitter and the same wire thickness.
What other type of capacitor can i use instead of an electrolytic capacitor
Any type of capacitor can be used but the value must be higher than 100uF
Sir Tp35C is heatup, and there is no voltage in Rx.
You will need a heatsink for it, but the circuit must oscillate first, there are many good videos on Youtube, please watch them…
Sir My circuit is running , but with 12V dc adapter, due to Transistor TIP35C. When I put 2N2222 transistor for 5V dc adapter then 2N2222 transistor is melting , So what is the method in which i can operate on 5V dc Adapter.
How can you say your circuit is running? Circuit will be running if the circuit oscillating with some frequency. If your connections are correct and your coils are correctly wound then you will get the results instantly. Check your two core wire connections with the transistor, turns must be tightly stuck with each there.
Sir, as shown in the images, the turns of Tx and Rx are same but thickness and thinness of Tx and Rx is different. But you tell me that Rx turns greater than Tx.
Sir, In your computerized Image the turns of Tx of 2 Core wire are 10…But at the below a real image in which the number of tutns are 20 of white 2 core wire???
20 is better, higher the number turns the better will be the results
Sam, there are fixed rules for making this project, everything is linearly proportionate. Lower Rx turns will give lower voltage output and vice versa.
Sir, as shown in the images, the turns of Tx and Rx are but thickness and thinness of Tx and Rx different. But you tell me that Rx turns greater than Tx.
If i used same 2 core Speaker wire for Rx coil Is it right???
Can I make 2.5 inches of diameter of Rx ?… Where Diameter of My Tx coil is 5 inches.
In 2 core Speaker wire of Tx of the wire guege number is 28 Can i use 18 number for receiver coil.
please do it as shown in the images, Tx wire should be thicker, and Rx wire should be slightly thinner. Rx coil must have higher number of turns than the Tx.
Sir what type of medium will used between coils and i have speaker 2 core wire is it right
Sir what type of medium will used between coils and i have speaker 2 core wire is it right
Sam, The medium is air core….yes two core speaker wire will do
Sir thanks to reply very soon,
Sir can i use sigle copper wire for receiver coil. How many turns give into receiver coil according to single copper wire , because 2 core speaker wire not adjust at my backside of phone , i give 20 turns of 2 core speaker wire in Tx.
Hi Swagatam, I wired a Receiver as per your design. I have coil dia. of 3 inches flat on paper with 28 swg enamel wire. I used a bridge for DC with 220 mf cap. The voltage shows 15 volts pulsating. But the moment I connect the cellphone the voltage drops to 4 volts. I am using Bluehive chinese Transmitter Rating Output 5 volts 1 Amo & 9 volts 1.1 Amp. Input 5 volts 2 amps & 9 volts 1.67 amps. Please let me know how I can improve or correct the receiver.
Hi Placid, it may be due to lack of current, or inefficient current transfer in the receiver section. Please try using thicker wire for the receiver coil, or use many thin wires in parallel instead of single thick wire for the receiver coil. Try the same for the transmitter coil also.
Hi Swagatam,
Thank you very much for quick response. After I sent my request, I made another coil with 18 swg. The current improved slightly and the voltage remained same. But the cellphone discharges instead of charging though the voltage was 5 volts (slightly fluctuating) Anyway as you have suggested I will keep trying Transmitter is a commercial brand Bluehive (chinese) so I am trying to use it and can’t do anything about it..
You are welcome Placid!
Yes, I think the problem could be from the transmitter also, since you are not able to change its winding thickness, moreover 5V 1 amp is just 5 watts which may not be enough for the modern smart phones.
The current from the transmitter must be at least 2 amps.
Hello sir its me again, first i would like to thanks to you for your great work, i have i managed to make the wireless power transfer worked using 1k ohm resistor & 12V 1A adaptor. How ever my output voltage only gets about 3V with 0 cm distance from coil so my question is how much voltage needed to charge a phone and how do i fix my circuit in order to get that specific amount of voltage? Tq sir hoping to hear from you soon.
Glad you could make it Ikmal, to increase the receiver voltage you will have to increase the number of turns of the receiver coil appropriately and also ensure that the current from the transmitter is high enough to sustain the voltage while the receiver output is loaded.
Hello sir, I want to ask a question regarding my project about wireless phone charger, are the number of turns of a transmitter coil must be bigger than the number of turns of a receiver coil? and how many turns the transmitter circuit and the receiver circuit needed? I hope you can explain to me. Thank you.
Hello Muhd, both the coils can be of the same dimension and specifications.
The turn numbers are given in the above article image.
Your website is impressive. mainly the Tesla related works. Can you please share the PCB (gerber) file of the bifilar coil ?