A Tesla coil is a device which generates high voltage, high frequency alternating current for the purpose of producing visible arcs. The most fundamental element of a Tesla coil is a primary coil consisting of a small number of turns of heavy gauge wire, coupled with a secondary coil consisting hundreds of turns of very small gauge wire, topped with some metallic object from which the sparks protrude, tuned to resonate at some predetermined frequency. There are several different Tesla coil topologies which use different methods of driving this resonator circuit:
- Spark Gap Tesla Coil – A High voltage AC source is used to charge a capacitor bank until a peak voltage is reached which is large enough to arc across a gap, allowing the capacitor bank energy to discharge into the primary coil. Simplest topology, but least efficient and least controllable as discharge rate is limited by the line frequency of 60Hz.
- Vacuum tube Tesla Coil – Uses a vacuum tube to switch current through the primary coil. More efficient than a SGTC, as the discharge rate can be synchronized with the zero crossing points of the AC input. However, it is still limited by the 60Hz line frequency.
- Solid State Tesla Coil – Uses modern power semiconductors (usually MOSFETs or IGBTs) to switch a DC source through the primary coil with a PWM controller. More efficient and the most controllable and flexible, but only the secondary circuit is tuned.
- Dual Resonant Solid State Tesla Coil (this project’s topology)– Identical to an SSTC but has a tuned primary and secondary resonator circuit. Less flexible than an SSTC but yields much higher output power and spark length.
- Quasi-continuous wave DRSSTC – Most complicated (and expensive!) topology which is similar to a plain DRSSTC, but has a high impedance primary circuit and a carefully controlled ramped DC input. This mimics the “ladder” spark growth seen in a VTTC and can produce sparks 10 times longer than the secondary coil.
From this point forward, information will be specific to this project. A more detailed explanation about the DRSSTC topology is in the theory of operation section.
Tesla Coil Parts and Terms
This section will outline all of the major components of the DRSSTC, as well as explain common Tesla coil terms that may be used throughout the document.
Inductive component of primary circuit. Consists of about 9.75 turns of copper tubing. Tapped at about 6.5 turns.
Inductive component of secondary circuit. Consists of about 1000 turns of 30AWG magnet wire wrapped around a 6.5” PVC pipe.
Capacitive component of primary circuit. Consists of 12 pulse capacitors which charge and discharge energy into the primary coil.
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