By Girish Radhakrishnan
Wireless power is an emerging technology in this present world. But the stunning fact is that it’s a century old concept. This concept was emerged by Nikola Tesla.
Charging batteries through wireless power is used in many high end Smartphones, electric cars, electric toothbrush, and wearable electronics like smart watches and so on.
The major problem of wireless power transmission is the efficiency. Today’s gadgets that utilizes wireless power has terrible efficiency, it can only receive 1/4th of the transmitted power.
Rest of them dissipated as heat and some lost as magnetic field. The range between transmitter and receiver is very short, at a range of few centimeters.
Before going for circuit diagrams and explanations here are some common myths people might think about wireless power transmission. Some people think that it is a dangerous protocol that will kill or injure you.
The fact is that, the power is transmitted in the form of pulsating magnetic field which won’t harm you and not electricity itself transmitted.
Some people might think, it says wireless so; it can be transmit power over a huge distance like radio waves. But that’s not true, wireless power utilizes nearly the same principle as transformer, but at high frequencies and without core.
However both the transmitting and receiving coils must be close as possible to achieve greater efficiency.
The proposed setup for illuminating an LED with wireless power transmission consists of transmitter and receiver circuits. The power is transmitted by 5+5 winded coil which is coupled with 4.7nf capacitor.
The receiving coil consists of 10 turns and also coupled with 4.7nf capacitor.
The coil diameter is around 5 cm both. This 4.7nf (C2 & C4) capacitor is responsible for efficiency, if the value is mismatched, for example: transmitter coil coupled with 10nf and receiving coil coupled with some other value, you may not get the correct result.
This is because the transmitting and receiving coil has resonant frequency.
Both transmitting and receiving coil’s resonating frequency must match.
The transistor BD139 should be mounted on a heat sink. C1 and R1 are oscillatory components which generate frequency in combination with transistor.
The frequency spikes are applied to coil, which generate alternating magnetic field around the transmitter coil. This field is picked up by the receiving coil and rectified by 1N4148.
Use a germanium diode with low forward voltage drop such as 1N4148. Use a red LED because some red LED has low forward voltage than green or blue colors, but other color LED will also work without any problem.
The coil can be made from electrical wire that lying around your house. See the prototype to get an idea on the coils.