The following is our paper published this October 2011.
Abstract
This paper reports on construction of a bipolar tesla coil and an investigation of the series inductor-capacitor (LC) driver circuit configuration by varying some parameters. Its primary circuit consists mainly of a tank circuit powered by a neon sign transformer (NST). The static spark gap serves as a switch and protector of NST and the high voltage (HV) capacitors. The capacitors are made up of car battery casings, the dielectrics are glasses to avoid breaching, and the electrodes are brass and copper plates. The primary coil is a copper tubing and wound into a helical form. The secondary coil is made of a long magnetic wire wound on an insulated pipe. The bipolar tesla coil was operated with varying values of the HV capacitance and number of turns of the primary coil so as to find the maximum voltage that it can produce.
1. Introduction
Tesla coil is a special type of transformer. It is an air-cored transformer working on its own resonant frequency used to generate very high voltage. Primary coil consists of few turns of thick wire (usually copper tubing wire), secondary coil is wounded by hundreds or thousands of thin wire on cylindrical skeleton.
There are many kinds of configuration for Tesla coils but here in this study, bipolar type of tesla coil is used. The secondary coil is mounted horizontally and the primary is centered at the secondary.
2. Methodology
In building the bipolar tesla coil, Series LC driver configuration was used.
2.1 Spark gap
The spark gap serves as a high power switch that is responsible for the discharge of the HV capacitor into the primary coil of the Tesla Coil. It turns on when sufficient voltage exists in it. The spark gap turns-off when the current flowing through it drops to a low level and the air regains its insulating properties.
2.2 High voltage capacitor
The high voltage (HV) capacitor stores charge and is mostly charged in a few milliseconds, and then fully discharged into a few feet of primary coil in a few microseconds. This gives rise to incredibly high peak currents, rapid voltage reversals and high dielectric stress but usually have very small capacitance for it to the discharge quickly. The HV capacitor uses glasses as dielectrics and Brass and Copper sheets as its parallel plates.
2.3 Primary coil
The primary coil is designed for very high currents. Therefore, the wire must be very thick. As the currents are of high frequency it is not needed to have massive wire because of the skin effect. Therefore, the copper tubing was a good choice.
2.4 secondary coil
The secondary coil is simply a long winding wire 1107 turns. When stimulated by the primary coil, it produces such oscillations. In doing this, the secondary coil will produce amazingly powerful oscillation and voltages anywhere from hundreds of thousands to the millions.
3. Result and Conclusion
The maximum experimental value of the capacitance was 13.89 nanofarad when the two HV capacitors were in parallel connection. The maximum output voltage produced is 203.2 kV.
Although the design of the primary coil is to produce high spark gap lengths on the ends of the secondary coil, most likely it is also directly proportional to the number of turns of primary coil. This is because the oscillating magnetic field of larger number of turns produced high voltage nodes than those produced by oscillating magnetic field of fewer numbers of turns.
The following video clips show the sparks of our bipolar tesla coil. I constructed it five years ago with Mr. Arlie Apduhan . . . The result of our tiresome efforts. :-)
Bibliography
1. Alcantara, P, and Hamoy, E., (2006) Design and Implementation of a High Voltage High Frequency Tesla Coil, undergraduate thesis.
2. Corum, J. F., et al., (2006) Six International Symposium Nikola
Tesla: Multiple Resonance in RF Coils and the FailureTesla Coils a
nd the Failure of Lumped-element Circuit Theory.
3. Corum, J and Corum K. (1994) Nikola Tesla, lightning observations,
and stationary waves, New York.
Acknowledgment
The authors would like to thank Mr. Alcantara, and Mr. Hamoy for the assistance and fruitful advices in making this project. And the Physics Department of MSU-Main for the support and encouragement to publish this work.
Time in Manila, Philippines 
