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# High Current Wireless Battery Charger Circuit

In this article we learn regarding how to design and make your own customized high current wireless battery charger circuit using wireless power transfer concept.

## Introduction

In many of my earlier articles I have comprehensively discussed wireless power transfer, in this article we will go a step ahead and try to learn how to design a high current version of the same which can be applied for any high power wireless transfer operation such as for charging an electric car battery etc.The idea of optimizing a wireless power transfer circuit is quite similar to optimizing an induction heater circuit, wherein both the concepts can be seen utilizing the optimization of their LC tank stage for achieving the desired power output at the highest possible efficiency.

The design can be implemented by utilizing the following basic circuit stages in it:

### The Transmitter Circuit will include:

2) A half bridge or a full bridge circuit (preferably)
3) BJT/Mosfet driver stage.
4) an LC circuit stage

### The Receiver circuit stage will include:

1) Only the LC circuit stage.

An example circuit for the proposed high current wireless battery charger can be witnessed in the following diagram, for simplicity sake I have eliminated the use of a full bridge or half bridge circuit, rather have incorporated an ordinary IC 555 circuit.

The above design represents the transmitter circuit of the high power wireless battery charger circuit using a IC 555 PWM circuit.

Here the output could be a little inefficient since the conduction process is single sided and not a push pull type.

Still, if this circuit is correctly optimized a decent high current power transfer can be expected from it.

### How it Works

The IC 555 is basically configured in its standard PWM mode which can be adjusted using the shown 5K pot, there's another adjustable resistor in the form of 1M pot which can used for optimizing the frequency and the resonance degree of the circuit.

The PWM pot could be used for adjusting the current level while the 1M for peaking the resonance level of the LC tank circuit.

The LC tank circuit can be seen attached with the transistor 2N3055 which powers this LC stage with a frequency corresponding to its base frequency from pin#3 of the IC.

### How to Select the LC Components.

Selecting the LC parts optimally can be achieved by following the instructions as furnished in this article which explains how to optimize resonance frequency of an LC tank network.

Basically if you know the frequency value, and either L or C, then the unknown parameter can be easily calculated using the suggested formula or this LC resonance calculator software.

The L inductor must be made exactly as shown in the diagram, that is it must be in a bifilar form for achieving best possible results in terms of wireless power transfer efficiency.

The center tap may be ignored, and only the two outer ends could be used wit the shown circuit.

The coil for the receiver circuit for this high current wireless battery charger need not be as complex as the transmitter coil. Meaning, you can simply use a single continuously running coil from start to end, and add a resonating capacitor across these terminals, as sown below:

Make sure the LC values are exactly similar to the Tx LC values. The set up can be seen in the following image:

The 2N2222 transistor is introduced to make sure that while adjusting the resonance, the 2N3055 is never subjected to an over current situation. In case this tends to happen the over current develops an equivalent amount of triggering across Rx sufficient to activate the 2N2222, which in turn shorts the 2N3055 base to ground inhibiting it from conducting any further and thus preventing the device from a possible damage.

Rx may be calculated using the following formula:

Rx = 0.6/Max current Limit of the transistor (or the wireless power transfer)

#### Adding a voltage regulator for charging the battery:

In the above diagram, the output from the receiver should be attached with a voltage regulator circuit such as using an LM338 circuit or an opamp controller circuit for making sure that the output can be safely fed to the intended battery for charging it.

### PCB Layout

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I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

### 24 thoughts on “High Current Wireless Battery Charger Circuit”

1. By saiying “Rx = 0.6/Max current Limit of the transistor (or the wireless power transfer)” do you mean that if I need to transmit 5A over the coils, Rx = 0.6/5 = 0.12?

What unit would 0.12 be? Ω or kΩ?

P.S. : I need to wirelessly charge a 5A 22.2V LiPo battery, do you think this circuit can handle it?

Thanks

• Yes that’ right, it will be 0.12, in OHMs. The formula is the basic Ohm’s law so the output will be always in Ohms, provided the current is taken in Amps and voltage in volts.

5A 22V wireless charging is certainly possible, but for this the input current will need to be above 5 amps, may be 7 amps, and the coil wires will need to be upgraded accordingly

• There are a few more things i’m not sure about :

– Calculating the IC555 frequency with 5k & 1M pot gives me a 1Hz to 300Hz frequency range. Isn’t that too low? Most QI charger on the market are in the KHz – MHz range…

– What’s the connection between the IC555 frequency and the LC frequency? Do they need to be identical?

– You say the PWM pot (5k pot) can adjust the current, isn’t the current decided by the load (receiver?)

• You are right, please reduce the capacitor value to 1 nF.
The 555 frequency must be adjusted to the LC resonance frequency for optimal performance.

The PWM restricts the output current regardless of how much the load tries to consume, so it’s like putting a cap on the current consumption so that the load is unable to go beyond a certain limit.
The 2N2222 additionally does the same.

2. how to select transmitter coil and receiver coil for wire less charger for 3.3 v to 12 v dc battery with auto charger ?

• The procedures and calculations are given in the article, you can easily work it out according to your requirement.

3. Good Morning Sir,
I want to attempt this project so, I would like to know this project is hardware implemented or not?

• Hi Bangaru, the concept has been tested using a different oscillator but not yet tested using IC 555

4. Dear Boss,
please support with Value of capacitor and resistance

also i need to make circuit for wireless battery 3Vdc charger.

mention circuit in this page can be implement the required ( wireless battery 3Vdc charger.)

thanks for kindly support

• Ahmad, the frequency and the tank capacitor will need to be found out by practical experimentation, and this will depend on the selected coil turns and inductance value. These can be tweaked and finalized only by piratical tests.

• what are the practical tests?
also how to measure the inductance value of the coil

• Inductance can be calculated using the following formula

L = (0.2 x d2x N2) / (3d + 9l =10b)
L = Inductance (in μH)
d = Diameter of the inductor coil (Inches)
l = Length of the indutor coil (inches)
b = Diameter of the coil winding wire (inches)
N = Total turns of wire

SORRY, this is for a normal coil not for bifilar coil…I’ll let you know soon

• Did you manage to find the formula for the bifilar coil?

• No I couldn’t find it, however it seems a bifilar coil is not required for the above circuit. A normal single core wire tightly wound is enough

5. please support as some component without data in DC Wireless charger diagram.

• you will have to calculate them with respect to the frequency….the software link for calculating is provided in the article. The frequency is created by the IC 555 circuit and adjusted by the accompanied pot.

6. This guy seems to have a whole bunch of badass projects. And I will always spend my time trying to recreate all of them just for fun. The only hard part is my funding, wish I could have been a teacher, thanks for sharing your schematics and taking the time and effort because I know how much every goes in the posting

• Good morning Dabasis, yes it is most probably due to lower current from the adapter unit that's causing a slower charging of the mobile battery and unable to match the consumption rate.

By the way while travelling how do you access the mains supply for the adapter? or are these adapters DC to DC types?

You can also confirm the amps from the two units by measuring them through a DMM or an ammeter.

Please provide the details of the adapter whether it's an AC to DC or DC to DC so that I am able to suggest improvements….

• Sir, so kind of you to try to answer and notify me so promptly. Input to the adaptor is from cigarette lighter socket of the car I use for traveling. The car battery is 12 volts. Though the adopters stated output current 1.7 amps, but practically it sure to be much less. I came to this conclusion because for testing when when I simulate same situation as I practically undergo while traveling by charging the mobile from the OEM supplied AC mains adopter of stated output voltage and current of 5.2 v and 1.2 amps respectively, the phone works fine even when I continuously fiddle the Google maps. The adopter continue to increase the amount of charge of the phone. Untimely the phone gets fully charged over a period of 2.5 to 3 hours. I hope you got the idea input and output of these DC to DC adopters. Regards

• Debasis, OK got it, so it seems to be a DC to DC adapter…

you can try modifying your adapter output by changing the wire thickness of the buck inductor associated with the IC.

You might have noticed that the circuit has an inductor, you will need to carefully remove the inductor, unwind the turns, and then take two exactly similar wires together and re-wind it with the same number of turns. this will hopefully increase the current output of the system and speed up the charging process.

8. please what is the current output and what's it range… thanks

• 6 inches

9. Well done and innovations