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# Just L or LC!

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#### Electronman

##### New Member
Hello,

These days I am working on an electromagnetic wireless power generator to transmit 10V up to 10cm for a LED.
The circuit uses an oscillator made by 555 chip and a 2N3055 as output driver (the oscillator has a volume to adjust the freq from 10 kHz up to 300 kHz).
The out put is connected to 8 turns of 1mm in diameters of wires, the diameters of the whole wound wire is almost 6cm. the other wound wire which is connected to the load (a small led) uses just similar windings.

Here are my questions:
1: Do I need to find the resonance freq of the winding or Do I need to (Or can) use a capacitor in parallel with the said winding and then find the resonance freq somehow and adjust the oscillator at that freq to improve the output power?

2: At now which I use the windings without any tuning circuit (I mean a capacitor in parallel with the winding) I get more power with increasing the oscillation freq but does everybody know which freq is the optimum freq for this circuit? Can I increase the freq up to 100MHz and get better result?

3: Is there any other way to generate wireless power other than electromagnetic? Something like sound or ultrasonic? Can I do such thing with ultrasonic too?

4: the last question is about RF and it arrived to me when I was thinking of the first question. If the oscillator is a chip which generates alternating pulses then can we use just an inductor at the output of the transmit the RF signals or yet we need a tuned circuit (LC for instance)???

You're using a coil that's way up in the radio frequency, much higher than your oscillator will run. Increase the number of windings and add a capacitor. The equation for resonalse is f = 1/2*pi*(LC)EXP(1/2) Find out the equation that relates the windings of the coil to the coil's inductance. I'm too busy to look it up right now.

Thanks,But I did not get the answers regarding to my question!

Why are you thinking that the coil is not good at that freq and why do you think that it is good only for RF?

The question is, why do you think it's good for your frequency? I plugged in your numbers and used the equation I gave above and an estimated value of 10pf for self-capacitance, and came up with a resonate frequency of around 90Mhz. Do the math, man.

Last edited:
Hello,

These days I am working on an electromagnetic wireless power generator to transmit 10V up to 10cm for a LED.
The circuit uses an oscillator made by 555 chip and a 2N3055 as output driver (the oscillator has a volume to adjust the freq from 10 kHz up to 300 kHz).
The out put is connected to 8 turns of 1mm in diameters of wires, the diameters of the whole wound wire is almost 6cm. the other wound wire which is connected to the load (a small led) uses just similar windings.

Here are my questions:
1: Do I need to find the resonance freq of the winding or Do I need to (Or can) use a capacitor in parallel with the said winding and then find the resonance freq somehow and adjust the oscillator at that freq to improve the output power?

2: At now which I use the windings without any tuning circuit (I mean a capacitor in parallel with the winding) I get more power with increasing the oscillation freq but does everybody know which freq is the optimum freq for this circuit? Can I increase the freq up to 100MHz and get better result?

3: Is there any other way to generate wireless power other than electromagnetic? Something like sound or ultrasonic? Can I do such thing with ultrasonic too?

4: the last question is about RF and it arrived to me when I was thinking of the first question. If the oscillator is a chip which generates alternating pulses then can we use just an inductor at the output of the transmit the RF signals or yet we need a tuned circuit (LC for instance)???

To be precise, you are trying to create a magnetic field coupler, not an electromagnetic power generator. All of the power will be coupled by magnetic field and virtually none by electric field. So, in this case, you can consider your system sort of like a power transformer where the magnetic field of the primary coil couples by mutual inductance to the secondary coil.

I believe that since you are trying to work at frequencies below 300 KHz, your coil inductance is far too low. Your coil needs to have many more turns on it, and should be wound on a ferrite core. Perhaps you should aim to have a coil inductance of about 1 mH. This will greatly increase the magnetic field. However, at the same time, you must maximize the current flow through the coil and since you are increasing the reactance of the coil, perhaps some compromise is needed to find the right coil inductance.

You can use a capacitor in parallel with your coil, once you have increased its inductance. Resonating the circuit with the capacitor will maximize the circulating current in the coil, which is good. It will also add some selectivity which may make the system operate a bit more efficiently.

The optimum frequency for such a system is dependent on many things, most importantly the coil, so there is a tradeoff of coil size/inductance to frequency. However, as you raise frequency, there is more chance of some other bad things happening, like decrease of efficiency, interfering with other devices, more difficult to build, etc., so it may be best to limit your experiments to frequencies below 400Khz.

Magnetic field coupling has been used many times to couple power over short distances, so the approach you are using is the most obvioius choice. However, another way that might be effective is to transfer energy using a fluid. The most readily available fluid is air. You could transfer significant energy by pushing air across the gap using a fan, and then use another fan to act as a generator pushed by this air.

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