Wireless Power Transfer Build

Built a simple wireless power transfer system following the resonant inductive coupling principle. Primary coil driven by a ZVS oscillator, secondary coil at the same resonant frequency.

The coil geometry matters: both coils should be the same diameter. I used 15 turns of 0.5mm magnet wire wound on a 60mm former. The resonant frequency with a 10nF capacitor in series was about 800kHz. Alignment between the coils is critical — off-center by 30% drops efficiency from 75% to 40%.

Practical efficiency at 3cm distance: about 70% electrical-to-electrical, measured by comparing input power (Vin × Iin) to output power (Vout × Iout). This is fine for charging small devices but not competitive with USB-C for anything power-hungry. The system transfers up to 2W cleanly.