Wireless energy transmission: practical troubleshooting of my setup

Discussion in 'The Projects Forum' started by TBJ, Apr 10, 2012.

  1. TBJ

    Thread Starter New Member

    Apr 9, 2012
    Hi all,

    Hopefully someone will be able to help me. I have just started messing with this stuff and I do not have much of a theoretical background, although I know the basics of resonant circuits and I am picking up the rest as I go.

    I want to implement a basic wireless energy transfer system (loose resonant coupling) for eventual use in a rotating POV display. I started with the basic ZVS driver circuit (intended for use as a flyback driver), wound a few different coils and started experimenting. Here is my setup:


    with this coil I was (from memory) getting an inductance of about .027mH, coupled with a 100nF cap for a resonant frequency of ~96KHz. The secondary here is matched.


    I also tried winding a higher-Q primary, which you see here. The inductance of this coil is unknown but I was able to achieve coupling by tuning the coil using the ferrite rod that you see. This one yielded slightly higher efficiency, but...

    With both of these setups I could not pull more than 60-100mA off the secondary, and certainly not enough power to blow up the LED (without current limiting), which is what I would have expected!

    Tuning the tank capacitance for higher frequency (up into the MHz range) reduced the efficiency still further.

    The driver is using 2n7000 MOSFETs which I know are pretty underrated, but they're not even getting hot at resonance. Current draw of the driver circuit is in the tens of mA range! Almost as though I am not injecting enough current into my primary circuit.

    Now, as I said, I'm just starting out in this stuff, so please be gentle. Could someone possibly suggest where I may be going wrong in these experiments?

    I'm not expecting great efficiency, but I have seen people light incandescent bulbs with a similar setup - yet I can't get enough power to blow a poxy LED. :)
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    I've never done what you're doing so take this with a grain of salt, Try using magnet wire instead of insulated (18AWG?) wire.
  3. wayneh


    Sep 9, 2010
    His coil wire appears to be single strand copper, possibly it is magnet wire. Can't tell whether it's insulated, but that shouldn't matter since the coils are not touching each other.

    Oops, sorry, now I see the other coils using insulated wire.

    A schematic would be helpful.
  4. chrisw1990

    Active Member

    Oct 22, 2011
    where did you originally come up with the design? it seems some thought and knowledge of these systems has been used.. be good to know where youve got that from? internet links or such?
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
    Please post a schematic. Is this a series or parallel resonant circuit?
  6. TBJ

    Thread Starter New Member

    Apr 9, 2012
    It is a parallel resonant circuit.

    The schematic of the driver circuit is here: http://wiki.4hv.org/index.php/Flyback_transformer#High_Power_Drivers

    As I said I am using 2n7000 FETs instead of the nice chunky IRFP250s, because I happened to have them around, but I'm not sure that is the problem (though I admit I haven't looked at their switching speed that closely!)

    The receiver circuit is just a simple tank circuit with an LED attached.

    Just general reading up. I should cite the following as a source:


    And also from general meddling with RF stuff - I've built a few radios and picked up some knowledge there, though not much.