Wireless Power Transmission

Hi everyone,

I am given a project to build a wireless power transmission system. I am suppose to transfer energy via inductive coupling from the transmitter side to the receiver side, and the energy will be used to charge a Li-ion based battery. I assume for my application a 5V, 500mA is needed to charge the battery. That means i need an output power of 2.5W. The allowed distance between those coils are around 2cm. any ideas anyone??

Thanx in advance

I have an electric toothbrush that recharges with out contacting the charger. The distance is almost zero. You will loose power! It might cost you 20 watts to get 2.5 watts. Break open an electric toothbrush charger and you will see it is simple. There is a company in Boulder CO USA that makes cell-phone chargers that way.

ronsimpson said:

I have an electric toothbrush that recharges with out contacting the charger. The distance is almost zero. You will loose power! It might cost you 20 watts to get 2.5 watts. Break open an electric toothbrush charger and you will see it is simple. There is a company in Boulder CO USA that makes cell-phone chargers that way.

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I do feel, in modern times, where power economy is much talked about, this amounts a heavy wastage.
Unless the situation really need such a method of wireless transmission of power.

<10% efficiency at a distance of just 25mm?

I don't think so, using a pair of tuned coils will make it more much efficient than that.

You can use a pair of small loop antennas (D<=0.1*lambda) to charge the circuit. they have poor radiation resistance, but their magnetic flux is tightly bound near the circumference of the loop., the field strength drops off as 1/r squared. but within close prximity you should get maximum coupling.

at my ast job, we had a technology symposium, and one phillipino engineer used the strategy of coils and loops to light up a bulb. not really efficient means of power transfer though.*

thank you for the ideas.

Efficiency is not my main concern here as long as i still manage to supply enough power for the battery charger, and of course the high power needed for the transmitting side doesn't fry the components there.

But i need more details such as what frequency to be used? How to drive the coils? Do i need power amplifier to generate higher fields?

Sorry for being a noob but this is my first practical project.

thanks once again.