Solid State Tesla Coil and Wireless Power



Version 1




This is a Solid State version of a Tesla coil. Eg, replacing the spark gap with Mosfet transistors and using a close coupled primary coil without capacitors. The method of driving the primary coil varies from design to design. After looking around the internet at various other peoples work, I set out to design my own. For version 1 this is just a fairly straight forward circuit, with a few protection devices. The next version will be more advanced, hopefully one which will include a self tuning system (as the output voltage drawn effects the resonant frequency proportionally).


The Secondary coil or resonator comes fromthe Tesla Coil v1 project. The Self resonant frequency of this coil with topload is 174Khz. So the driver will need to produce a frequency that matches this.


This is where my setup differentiates from others in that I use only 2 mosfets to drive the coil. To do this I use two primary coils. One wound clockwise up the base of the secondary and one wound counterclockwise down over the top of the first primary coil. Both a of equal length wire and of the same guage. The center or top end of the two primarys are joined together and are connected to the poisitive 44v rail. The 2 mosfets serve as switches to ground for the two primarys, creating and AC system (The TC secondary will actually see a sinusoidal waveform due to the LC circuit).


The coupling coefficient will only be marginally effected by doing it this way and also saves using extra mosfets for a full H bridge driver.


The Circuit:


The IC I have used for the SSTC is the well known TL494 Switch mode power supply controller. The design is very similar to my Plasma Sonic Speaker driver and incorporates some of the techniques used in that project.



Above: TL494 output from the 2 driver sections


The circuit is pretty self explanatory. The only thing that may need clarification is the ground return from the secondary. As I am using a transformer from the mains to produce the 44V to drive the primary, I am simply using the negative side (circuit ground) of this as my HV ground. This is contrary to normal TC's as they state you must use a solid earth ground. I have not experienced any problems with doing it my way, but please bear this in mind if you find equipment in your house being dissrupted. Just make sure you use large and small capacitors across the circuit supply to catch any noise (even rf chokes on the power lines maybe a good idea for high power levels).


The specs for the Tesla Resonator can be seen on the Tesla Coil V1 page. The primary wire used is solid copper 13A household cable and is wound like this; Direction: CW For:12T, then: + center tap, Direction: CCW back over the top of CW For: 12T.


Mosfets used in this circuit are IRF740's (or FQA55N10), these are ok but this experimentor has found that there are far better mosfets to use than these. The next revision will use these, STW20NK50Z.


Full Circuit Schematic Here


Wireless Power:


Another technology that was demonstrated by Nikola Tesla, is the Wireless transmission of power. He demonstrated this from his laboratory in Colorado Springs and achieved a transmission distance of over 25 miles.


The concept is simple. You take two identical secondary coils, use 1 as the transmitter and one as the receiver. These form a "tuned system", whereby signals presented to the transmitter and sent to the receiver.


The system is incredibly good and very effecient. I have personally achieved a distance of just over 1 meter, not amazing, but I am limitted at the moment by the mosfets I am using. The RX secondary ground is connected to the 44V negative rail (this could also be the earth if you use the earth for the TX coil, in this way, the distance between them can be increased).


The receiving coil has a 12 Turn primary coil around the base. The output from the primary is connected to a 240V 25W incandescent bulb. When the transmitting coil is powered up, the bulb glows to about half brightness! This is quite amazing since I am only feeding in about 60W of power. It has also been noticed that the receiving coil emits rf power as well. Fluro lights can be seen to glow around the receiving coil's secondary coil.


The transmission between TX coil and RX coil seems to be line of sight for maximum output. This is the same as normal radio transmissions. The output power from the receiving coil can be altered by moving your hand close to the RX secondary or blocking the line of sight. The RX topload can be touched quite safely (Which makes for a good demonstration!)


Above: setup for wireless power


Above: The bulb glows, meter reads 300VAC, current unknown as meter fails to read it! Probably noise from the proximity to HV RF. (Guess 20w/300vac = 60mA or less)


The wireless power transmitter was also setup outside and the earth used as the circuit ground, thus making the receiver coil totally independant from the transmitter circuit (true wireless power). The operation was exactly the same and efficiency is calculated to be about 60% power transfer between the two coils at a distance of 2 meters. Maximum distance achieved outside with the above setup and a total input power of 60w was about 2.5 meters before the bulb extinguished. A simple diode, resistor and LED (Red 2.5v 20mA) in series was also tested on the receiver coil primary output to see if the range could be increased. But an increase of only about 1m was accomplished before the voltage dropped too low to be useful.



Above: Wireless power demonstration setup outside, transmitter on the left and receiver on the right with a lit 25w bulb. The experimenter (me) with a 5ft flurotube behind.



Wireless Power RX Setup
SSTC Setup
Back EMF Diode and capacitor board
IRF740's on heatsinks, isolated from each other
Driver board during testing phase
TX Primary coil




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