Wireless charging experiment

Dear all

I posted a while ago about this. My student now has a wireless charging (qi) kit, which he promptly melted the components on the circuit board. I have an ipc signal generator and amplifier, and have tried using this to apply a voltage directly to the coil bypassing the circuitry. We then rectified the output of the other coil and managed to get up to around 4V at a very high frequency.

But I'm not an expert on electronics and am thinking experiments like this could damage my sig gen. The resistance of the coil is only around 1 ohm and so when this is used without the output coil in proximity (which I have connected across a resistor) then it could draw too much current from the sig gen? It has two impedence outputs 8 ohm and 600 ohm (off top of my head). Any advice on this would be most welcome.

Thanks in advance

Nick Mitchener

I'm not an electronics person but my understanding is the 8 ohm out put you use with a speaker or vibration gen and the 600ohm with an oscilloscope.

It's the impedance of the coil that the sig gen sees as it is an AC output. I don't think the coil on a speaker has a very high resistance. I only include a resistor if there is no coil in the circuit.

Maybe I'm wrong?
Thank you, Nick

Did the investigation today using 4 ohm (or 8) output and student was able to get different readings for rectified dc output from other coil, and I haven't melted my signal generator (rectifier connected to voltmeter which I suppose limits the current in both coils when they are in proximity). Will be interesting to see results. We also noted higher output voltage spikes at specific frequencies due to the resonant coupling, which is interesting.


I'd check the maximum current the sig-gen can deliver and vary the output level so it doesn't exceed this figure. Then hope this is enough to do the job! I think ours (Unilab) can give 2 or 3A from its low impedance output. If your voltmeter doesn't like high frequency ripple, try a small capacitor after the diode to ground to smooth out the waveform.