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# Wireless transmission of electricity

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#### Cecemel

##### Member level 5
Hi everyone,
I have some questions about wireless electricity.:bang:

1. Is there any max voltage or amperage you can safely transmit? :bsdetector:
(for example, if i would be holding a metal object and i would hold it close to the transmitter or if the transmitter would get close to electronical equipment like a computer, smartphone, tablet, ...)

2. How about the efficiency? Are there any variables for it?

3. What role does the frequency that you feed in the transmitter coil play?

4. I now that if you had more turns on the reciever coil then on the transmitter coil the volage would increase but is there any difference between for example having
10 turns on the transmiter and 10 turns on the reciever and having 20 turns on the transmitter and 20 turns on the reciever?

Regards,
Cecemel;-)

1. There are safety limits on the power density of a aerial with respect to humans. At low frequencies its 100v/m at VHF and above its 10mW/cm^2
2. Low, 10% would be good.
3. For a given coil size the higher the frequency the better.
4. Its the ratio of the number of turns that count.
Frank

The question is somehow boundless. "Wireless energy transmission" refers to short distance magnetic coupling in many cases, respectively it achieves high efficiency at low frequencies (100 kHz range).

Sorry i forgot to mention. I probably will be using this circuit below (but without that 7805 regulator), the distance between the coils will be only a few millimeters. I would like to use the receiver coil to charge a battery, to charge it at 1C I would need about 40w. If I feed the circuit 12 volts and 20 amps (computer psu), would I be able to get 40w out? (20-30w is also okay but not much lower because then the charging wil take over 2 hours)

Last question,
...respectively it achieves high efficiency at low frequencies (100 kHz range).
What do you mean with "high efficiency"?

Cecemel

The self-oscillating MOSFET inverter is a rather bad design, it's neither guranteed to oscillate at all nor to keep the transistor maximum ratings.

The self-oscillating MOSFET inverter is a rather bad design, it's neither guranteed to oscillate at all nor to keep the transistor maximum ratings.

Yeah... Would something based on a 555 be a better solution? I don't have used a 555 yet. Do you have a circuit that could let me adjust the frequency (maybe 50-200 kHz?)

Cecemel

A switch mode converter controller like SG3525 is probably better suited, 555 should be used with a flip-flop to generate symmetrical gate signals for two transistors. The advantage of the self-oscillating circuit is that it automatically meets the LC resonance frequency, an external controller must be tuned to it. But it promises better switching with less transistor heating.

A switch mode converter controller like SG3525 is probably better suited, 555 should be used with a flip-flop to generate symmetrical gate signals for two transistors. The advantage of the self-oscillating circuit is that it automatically meets the LC resonance frequency, an external controller must be tuned to it. But it promises better switching with less transistor heating.

Okay, do you have a circuit for this?

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