I am trying to make a wireless charger for a small handheld device. I've tried searching on the internet for something read-made, but everything I could find was much larger than I could fit.
The way I understand how wireless power works is that you basically have an air-core transformer with a 1:1 turn ratio - which in theory should pass the power through the air. I therefore made two little coils of 0.1mm magnet wire with ~250 turns each and with a resistance of 15 Ohms.
I used an H-Bridge driver to create a square AC voltage with peak to peak of 5V on the primary coil, but even my best attempt only created ~1V RMS on the secondary coil. The main problem is also, that if I try to power anything from the secondary, the voltage immediately drops to 0. My ampmeter registers 2µA flowing in the secondary, while it consumes up to 1A on the primary (which makes the primary very hot).
I tried with AC frequencies from 100 Hz to 60 kHz and I had the best results with around 4-10 kHz.
I thought I could just rectify the output of the sec and use those 5V to charge my battery, but this is apparently more complicated than I thought :)
Do I need some sort of resonating circuit? What am I doing wrong? Any help is much appreciated