DIY Wireless Power Transmission System

1. Project Overview & Story

Have you ever wondered how electrical energy can leap across thin air to illuminate a bulb without a single connecting wire? Wireless power transmission (WPT) is no longer confined to futuristic labs—it powers modern smartphones, electric vehicle charging pads, and biomedical implants. In this project, we construct a high-frequency resonant wireless electricity transmission system based on the principles of electromagnetic induction and push-pull resonant oscillation (often referred to as a ZVS / Royer oscillator variation).

This guide breaks down the circuit into modular building blocks, explains the physics behind each component, and provides a clear step-by-step DIY assembly manual complete with precise video screenshot capture locations for your Hackster project page.

2. Bill of Materials (BOM)

Below is the complete text-based component list required to build this project. No proprietary PCB is strictly necessary; it can be assembled on a standard prototype board or breadboard with short lead lengths.

A. Hardware & Electronic Components List:

· Transistors (x2): IRF2807 / IRFZ44N / IRF540N N-Channel MOSFETs - High-speed, low Rds(on) power MOSFETs configured as a push-pull switching pair.

· Voltage Regulator (x1): LM7812 12V / 1A Linear Voltage Regulator - Steps down the 18V DC input to a stable, low-noise 12V DC rail for precision oscillator operation.

· Gate Drive Resistors (x2): 470 Ω (or 4.7 Ω - 47 Ω range) 1/4W Metal Film Resistors - Limits gate charge current spikes and sets switching transition speed.

· Gate Pull-Down Resistors (x2): 10 kΩ 1/4W Resistors - Ensures positive MOSFET gate discharge and prevents false turn-ons when driving signals subside.

· Resonant Tank Capacitor (Transmitter) (x1): 0.47 µF High-Frequency Metallized Polypropylene Film Capacitor (CBB/MKP) - Pairs with the transmitter coil to establish the primary resonance frequency.

· Fast Recovery Diodes (x2): BYV26E / BAF26E Ultra-Fast Recovery Diodes - Cross-connected drain-to-gate protection diodes that shunt reverse inductive spikes away from the MOSFET gates.

· Zener Diodes (x2): 10V 1/2W Zener Diodes (e.g., 1N4740A) - Clamps gate-to-source voltage (Vgs) at ~10V to shield gate oxide from high voltage stress.

· Resonant Tank Inductor (x1): 100 µH Toroidal High-Current Choke Inductor - Acts as the DC feed choke to supply power while maintaining high AC impedance to the LC tank.

· Transmitting Coil (x1): 9 + 9 Turns Center-Tapped Flat Pancake Spiral Coil (Wound from 1.0mm enamelled copper wire) - Generates the intense high-frequency alternating magnetic field.

· Receiving Coil (x1): 18 Turns Flat Spiral Coil (Wound from 1.0mm enamelled copper wire) - Captures magnetic flux and converts it back into AC electrical energy.

· Resonant Capacitor (Receiver) (x1): 0.44 µF High-Frequency Film Capacitor - Connected in parallel across the receiving coil to match the resonant frequency of the transmitter.

· Load Indicator (x1): 12V Incandescent Bulb or Miniature Automotive Filament Bulb - Serves as both the electrical load and visual power transmission gauge.

· Power Supply (x1): 18V DC / 2A Power Adapter or Bench Power Supply - Supplies input power to the voltage regulator and LC tank driver stage.

B. Tools & Equipment List:

· Soldering Iron (30W - 60W) & Lead-free / Rosin-core Solder

· Enamelled Copper Wire (18 AWG / 1.0mm diameter) for coil winding

· Perfboard / Stripboard or High-Current Breadboard

· Wire Strippers, Flush Cutters, and Heat Shrink Tubing

· Multimeter (DC Voltage and Resistance Measurement)

3. How the Circuit Works (Theory & Block Diagram)

The wireless power transfer system operates in three main functional blocks:

· DC Regulation & Power Rail: The 18V DC power source is passed through an LM7812 voltage regulator, providing a ripple-free 12V supply to stabilize the driver stage.

· High-Frequency Push-Pull Oscillator: Two N-Channel MOSFETs alternate at high speed to convert DC voltage into high-frequency AC. The 0.47 µF capacitor and the 9+9 turn pancake coil form an LC resonant network that defines the resonant frequency f = 1 / (2π√(LC)).

· Magnetic Coupling & Resonant Receiver: The transmitter coil emits a localized alternating magnetic field. When the 18-turn receiver coil enters this magnetic field, an alternating voltage is induced. The 0.44 µF capacitor on the receiver matches the transmitter's frequency, maximizing energy capture and lighting up the 12V bulb.

4. Step-by-Step DIY Assmbly Guide & Video Screenshot Directives

Step 1: Positioning the Heart of the Circuit – Dual N-Channel MOSFETs

Mount the two IRF N-Channel MOSFETs onto your circuit board. These MOSFETs function as high-speed electronic switches working alternately. When one turns ON, it pulls its side of the center-tapped coil to ground while the other is OFF. This push-pull switching action converts direct current (DC) into high-frequency alternating current (AC), creating the initial alternating magnetic field.

Step 2: Integrating Power Regulation – LM7812 12V Regulator

Install the LM7812 linear voltage regulator. Because external power adapters can fluctuate or deliver higher voltage (e.g., 18V), the LM7812 smooths and reduces the incoming DC voltage down to a stable 12V DC rail. This ensures that delicate gate driving components and high-frequency timing circuits receive a constant voltage foundation, protecting the MOSFETs from over-voltage damage.

Step 3: Installing Gate Drive Resistors for Switching Timing Control

Connect the gate timing resistors (470 Ω / 4.6 Ω) directly to the Gate pin of each MOSFET. These resistors limit the initial gate charging current spikes from the driver stage and dampen parasitic high-frequency ringing. Controlling the gate rise/fall time directly optimizes the MOSFET turn-on/turn-off speed, which is critical for minimizing switching power loss and maximizing overall energy transmission efficiency.

Step 4: Adding the LC Tank Primary Resonant Capacitor

Place the 0.47 µF high-frequency polypropylene film capacitor across the transmitter tank output. This capacitor forms a parallel LC resonant network together with the primary transmitting coil. The specific combination of capacitance (C) and coil inductance (L) predetermines the natural oscillation frequency of the circuit, establishing a clean high-frequency AC oscillation required for inductive power transfer.

Step 5: Connecting Ultra-Fast Recovery Protection Diodes (BYV26E)

Install the two BYV26E fast recovery diodes connected in reverse parallel (cross-connected from the Drain of one MOSFET to the Gate driving circuit of the other). When a MOSFET switches off rapidly, the inductive coil generates steep, high-voltage back-EMF reverse spikes. These ultra-fast diodes quickly clamp and discharge these voltage spikes, safeguarding the MOSFET junction from voltage breakdown.

Step 6: Adding 10V Zener Diodes for Gate Oxide Clamping

Place a 10V Zener diode between the Gate and Source of each MOSFET. MOSFET gate oxide layers are fragile and easily destroyed if Vgs exceeds 20V. The 10V Zener clamps the maximum gate drive voltage safely around 10V, ensuring rapid switching into full saturation while shielding the internal gate oxide from transient overvoltage.

Step 7: Installing 10kΩ Gate Pull-Down Resistors

Solder two 10 kΩ pull-down resistors between the Gate and Source (Ground) of each MOSFET. When the opposite driving cycle ends, these pull-down resistors rapidly bleed off residual gate charge, forcing the MOSFET into a clean, decisive OFF state. This eliminates floating gate states and prevents disastrous simultaneous conduction (shoot-through) of both MOSFETs.

Step 8: Connecting the Main Resonant Tank Feed Inductor

Insert the high-current toroidal feed inductor ( choke coil ) into the positive DC supply rail feeding the center tap of the transmitting coil. The inductor serves two key roles: it acts as a constant current source feeding the LC tank, and it blocks high-frequency AC oscillations from traveling back into the LM7812 voltage regulator and main DC power line.

Step 9: Winding and Connecting the Transmitting Pancake Coil (9+9 Turns)

Wind the primary transmitting coil using enamelled copper wire in a flat spiral (pancake) geometry, consisting of 9 turns, a center tap, and another 9 turns (9+9 total). The flat spiral design concentrates magnetic field lines outwards into free space rather than confining them internally. Connect the two outer ends to the MOSFET drains and the center tap to the feed inductor output.

Step 10: Assembling the Wireless Receiver Coil and Resonant Capacitor

Construct the receiving module: wind a separate 18-turn flat spiral coil and solder a 0.44 µF capacitor directly across its two leads. This forms a secondary LC resonant circuit. When placed near the transmitter, the magnetic field induces AC voltage in the coil. Tuning the receiver resonance to match the transmitter (magnetic resonance) drastically increases energy capture range and efficiency.

Step 11: Attaching the Load Indicator (12V Filament Lamp)

Connect a 12V miniature incandescent bulb across the output terminals of the receiver coil circuit. The light bulb acts both as a functional consumer load and a real-time visual power indicator—its brightness dynamically reflects the intensity of magnetic coupling and wireless power transfer.

Step 12: Powering Up and Testing the Wireless Transmission System

Connect the 18V DC power supply to the main input. The LM7812 lowers the supply to 12V, initiating oscillator action. Gently bring the receiver coil closer to the transmitting pancake coil. As the receiver enters the alternating magnetic field, electrical current flows wirelessly through air, illuminating the bulb brightly!

5. Testing, Tuning, and Maker Optimization Tips

To ensure maximum energy transmission and prevent component overheating when building this project for Hackster, follow these expert hardware tuning guidelines:

· Resonant Frequency Matching: Ensure the receiver LC product (L_rx * C_rx) closely matches the transmitter LC product (L_tx * C_tx). Magnetic resonant coupling falls off dramatically if tuning frequencies deviate by more than 5%.

· MOSFET Heat Dissipation: Although push-pull ZVS-style switching is highly efficient, attach small aluminum heatsinks to both IRF MOSFETs if operating continuously above 15V to prevent thermal shutdown.

· Coil Geometry & Wire Thickness: Use thick multi-strand Litz wire or 1.0mm+ enamelled solid copper wire for pancake coils to minimize Skin Effect losses at high operating frequencies (100kHz - 300kHz).

· Power Supply Decoupling: Add a 470 µF electrolytic capacitor across the 18V DC power input terminals to buffer voltage sag during sudden load changes.

6. Conclusion & Next Steps

Congratulations! You have successfully built and analyzed a high-frequency Wireless Power Transmission system. By pairing simple discrete semiconductor switches with LC resonant circuits, high-voltage high-frequency AC creates electromagnetic waves that span physical gaps to perform useful work. Try experimenting with different coil diameters, adding a full-bridge rectifier to power microcontrollers like Arduino wirelessly, or building an acrylic enclosure for a finished tabletop.