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In the current market, the chargers are only 40-50% efficient.

  • How much is the conversion and flux losses during transmission?
  • Is there any way to improve the overall efficiency?
  • Can a ferrite core help to reduce the losses?
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Because it's a transformer with poor coupling between the primary and secondary, because it's an air core so it permeability is not good (I.e how well magnetic field can pass through) and the turns on the secondary are few. So if you have poor coupling and low secondary inductance, how do you get a few watts in the secondary? Pump lots of power in the primary of which alot does not pass across. This energy is therefore wasted thus lower efficiency. Fast chargers scale this so often wireless fast chargers have fans or large heatsink because the primary energy is much higher.

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  • \$\begingroup\$ What if I use ferrite plate on the surface of the charging pad and place the phone top of it. Will efficiency be any different? \$\endgroup\$ – Shane Studio May 20 at 18:02
  • \$\begingroup\$ No. The problem isn't the primary. It's the use of an air core and low secondary inductance/ coupling. \$\endgroup\$ – sidA30 May 23 at 0:34
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A 3kW EV charging system has an efficiency of 93-95%, so not all wireless chargers are inefficient. But I assume you're talking about a wireless phone charger. The coils used to generate a magnetic field usually cheap and have a lot of leakage flux. This is due to the way a magnetic field is induced in a wire. If you think about the fields generated by the coil, the phone's internal receiver for this energy cannot cut through all of the flux.

In addition to the flux, poor air coupling, the skin effect and also uncertainty in the value of inductance also cause a lower efficiency, as in this case the circuit may not be exactly in resonance.

As you said, a ferrite core can be used to increase the magnetic flux, which also adds to efficiency.

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  • \$\begingroup\$ Thank you for your answer. What if I use ferrite core in the receiver coil. Why most companies are not using ferrite in the receiver coil. Maybe that would solve the efficiency problem. \$\endgroup\$ – Shane Studio May 20 at 18:00
  • \$\begingroup\$ That would cause the ferrite core to be heated, even more power would dissipate. You can't do that in this scenario. \$\endgroup\$ – Danyaal May 21 at 17:42
  • \$\begingroup\$ What if I increase the frequency over 100KHZ. I heard ferrite is very efficient with higher frequency. There is very low saturation. \$\endgroup\$ – Shane Studio May 23 at 6:31
  • \$\begingroup\$ Unsure sorry friend. \$\endgroup\$ – Danyaal May 23 at 22:52

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