Mini Tesla Coil
A tesla coil is a device takes a low voltage and steps it up extremely high in order to wirelessly transmit electrical energy; it is a specific type of transformer. This project consists of two circuits/coils: a slayer exciter circuit using a BJT, and a similar oscillator using a MOSFET.
The Slayer Exciter Circuit consists of a single 2n2222 BJT and the primary and secondary coils of the tesla coil concentric transformer (the iconic tower). The primary coil consists of very few turns (I used 1-3), while the secondary coil consists of upwards of 1000 turns (though this can vary, mine range from 200-600 turns), this allows the voltage to be stepped up and thus transmit through the air.
The Slayer circuit and otherwise acts as a simple oscillator taking a DC voltage input and giving an AC voltage to the coils. The MOSFET circuit has a variable resistor in it to tune the frequency so that it oscillates at the transformer's resonant frequency, thus maximizing the voltage on the secondary coil.
This is my first experiment with Tesla Coils and high voltage devices providing me with the learning experience of what problems I may encounter in the field working with such devices. I'm also forced to exercise more caution around high power circuits than what I normally experiment with (low power data lines).
The first design I followed used this schematic. The secondary coils were wound using 28 gauge (0.3mm diameter) wire; the one shown below has roughly 250 turns.
The first test went well, other than that the secondary coil was too small, so I did not reach high enough voltage to transmit through the air. As can be seen in the videos below, I test to confirm the current is AC by using an LED in both directions, and can manipulate the surrounding field with my hand as a capacitive contact. The capacitve load on the top is a bouncy ball covered in aluminium foil (the medium coil is a golf ball, and the large coil is a toy car wheel). It is important to this load as it lowers the resonant frequency, lightening the load on the components used, especially the transistor.
I constructed more secondary coils, a medium sized one with roughly 230 turns with a larger diameter, and a taller one (shown below) with roughly 560 turns.
The second iteration I went to used a MOSFET in this circuit rather than a BJT. This allowed me to attach a makeshift heatsink because the form factor was different as well as experiment with various transistor and SSTC types. More information about this circuit can be found here.
I had to change some values of the circuit from the original schematic: the 50Ω resistor was replaced by a 180Ω while the variable resistor was changed from a 1kΩ to a 10kΩ due to old hardware unable to provide adequete performance. Note that these resistors are rated for a higher power than what are used in small radio applications such as RC cars (mine were scrounged from an old radio/cassette player). When I transfer the circuit to a permanent board (after further tests with higher voltages), I will exchange the heatsink for a more powerful one as the current one does not alleviate much stress on the MOSFET.
Here are some videos showing the transfer of power to a fluorescent lightbulb and plasma arcs through the air.
I then transferred the circuit from the breadboard to a protoboard and affixed it to the inside of the stand. The heatsink attached to the IRF540 is connected to the drain, so in this circuit it is connected to the input voltage.
While this is a problem mainly for protoboards, I found that I had a hole filled with solder that connected to ground (circled in red), and the contact between the heatsink and this point created a short. I would advise keeping an eye out for such simple mistakes whenever you're working with circuits.
After placing the circuit inside and fixing everything in place, I ran it more and noticed the streamers (the purple plasma arcs) were nearly twice as long as before.
A list of resources I consulted (note that not all are relavent to this specific project, but good for the understanding): 1, 2, 3, 4, 5, 6, 7, 8
NOTE: Tesla Coils and high voltage devices are dangerous. Exercise caution when experimenting with these devices. Tinkering is best when everyone is alive.
Last Updated: 05.14.2018
Project Type: Hardware