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I have currently designed a wireless power transfer circuit which is based on the ZVS principle and Royer circuit.

The issue I am currently facing is that the receiver coil is warming up a fair bit, depending on which variation of coil and resonance I use.

I have tried changing and tuning the capacitors on the receiver side (circuit can be seen here) close to, exactly and also with a detuning of about 30% more of the resonance set on the transmitter side. The coil on the receiver side is still heating up.

I think the problem is because of losses such as eddy currents, and maybe not the current tuning of the receiver, as I didn't take into account the tolerance of the film capacitors on the Tx side.

Is there a way to decrease the heating effect of the Rx side coil? How can one go about it?

I have tried using ferrite foil and they seem to help a little bit, but not too much. Would better tuning on the Rx side help with the heating issue, or is there something I am missing? Maybe changing the Rx design similar to this?

LC tank circuit for the Rx side.

Extra information.

  • Tx coil: 760308100110, 24µH
  • Rx coil: IWAS3222CZEB190JF1, 19.6µH
  • Measured Coupling factor K: 0.307 using LCR.

Edit 1:

Rx circuit

The capacitors used for the Rx circuit are C0G.

I noticed that the closer I got the capacitor value on the Rx side to achieve similar resonance, the power usage stays the same, but more current is drawn with less voltage.

When I have only the Tx coil connected, i.e., without the receiver coil placed near it, I measured a switching frequency of about 112kHz. I am assuming this is because of the losses.

Case 1:

  • Tx side-> 24µH, capacitor = 55nF, Fres = ~137kHz
  • Rx-> coil->19.6µH, capacitor = 66nF, Fres = ~140kHz
  • switching frequency = 112kHz
  • Vin: 11.9V,0.7A
  • Vout: 20V,0.2A

Case 2:

  • Tx side-> 24µH, capacitor = 55nF, Fres= ~137kHz
  • Rx-> coil->19.6µH, capacitor = 99nF, Fres= ~114kHz
  • switching frequency = 125kHz
  • Vin: 8.6V,0.96A
  • Vout: 20V,0.2A
JRE
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EmeraldMonk
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    You suggest changing the design to the design in the picture but, you didn't explain/diagram the current receiver coil design. Tuning capacitor types and values are important btw (as well as operating frequency) – Andy aka Feb 15 '23 at 14:38
  • Just wanted to make sure that my expectations are not too high. Currently the receiver coil in a a plastic housing, with not much ventilation. It has a thermal foil behind it to spread the temperature properly. transferring transferring 20V,0.2A for about 40 mins. The measured temp on Rx housing was about 50 degrees. Is this something that is normal and to be expected, or it means that my values are not properly selected, hence the increased losses causing increased heating of the coil? – EmeraldMonk Feb 21 '23 at 09:18

1 Answers1

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Maybe a mistake on my part that I did not simulate the receiver circuit. After much trial and error I was able to reach a optimal capacitor value which allowed the circuit to run with a stable temperature after long running time. What I learnt from this is the same what is given in many books and online resources. The capacitor value along with the inductor value of the receiver coil needs to be tuned properly in order to reduce losses, and in turn reduce the heating effect of the Rx coil.

JRE
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EmeraldMonk
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