As with any specialized hobby, coiling has its own brand of technical jargon. Likewise, many of the folks who post on the Tesla Coil Mailing List use a mix of technical jargon, acronyms, and abbreviations to save time and typing. For people new to the hobby, the postings can read like a foreign language. Coilers don't use this sort of lingo to scare away prospective members, it's just a convenience to avoid typing out some of the rather verbose terms related to coiling. I'm sure I overlooked a few terms, but these will help you translate the majority of "alphabet soup" postings. Of course, some coilers like to invent new acronyms and abbreviations as they go along. Not much I can do about those! Happy reading.
Air Blast Gap - A static spark gap in which quenching is assisted by blowing out the arc with forced airflow from a blower or air-compressor.
Arc - Intense, high-current electrical discharge, usually over a very short distance, such as that produced by an arc welder or a static gap.
ARSG - Asynchronous Rotary Spark Gap. A rotary spark gap whose break rate is not related to the AC line frequency.
Ballast - Anything used to limit the current of non-current limited transformers such as pole pigs. A ballast can be resistive or reactive. Examples of resistive ballasts include light bulbs, electric stove elements, water heater elements, etc. The most common reactive (inductive) ballasts are chokes, arc welders, variacs, or modified transformers. A capacitor can also be used as reactive ballast, but this is rarely done. Also a verb, as in, "I need to ballast my pole pig before it burns my house down".
Bang - Slang term referring to a single pulse discharge of the tank capacitor across the spark gap. Often used in technical discussions about disruptive tesla coil performance, as in "bang size" or "bang rate". See also BPS, Joule.
Bombarder - Also bombarder transformer. A high-voltage, high-powered transformer sometimes used as a Tesla coil power supply. This is a specialty item used in the neon sign trade to purify and de-gas the glass tubing prior to final gas fill and sealing. The bombarder resembles a scaled-up NST, and can deliver power levels on par with a smaller pole transformer. It is usually paired with a variable ballast called a slide choke to allow easy adjustment of the output current. The bombarder makes an excellent Tesla coil power supply. Unfortunately, they are so rare and expensive that their usefulness to the hobby is very limited.[click here for picture]
BPS - Also Bangs Per-Second; bang rate; break rate; pulses per-second; PPS, etc. Breaks Per-Second. The number of times per second a disruptive-type Tesla Coil undergoes a charge/discharge cycle. The term is used almost exclusively to describe RSG performance, but it is equally applicable to the static spark gap.
Break Rate - See BPS.
Cap - Capacitor.
Capacitance - How much charge a capacitor can hold. The standard unit of capacitance is the farad. This unit is too large for most electronics applications, so capacitance is usually expressed in fractional units. Common fractional units for radio frequency (and Tesla coil) work are uF, nF, and pF. uF means "microfarad", or 1/1,000,000 of a farad. nF means "nanofarad", or 1/1,000,000,000 of a farad. pF means "picofarad", or 1/1,000,000,000,000 of a farad. For example: .001uF = 1nF = 1000pF; get it?
Coiler - A person engaged in the Tesla coil hobby.
Coiling - Active participation in the Tesla Coil hobby. Building Tesla Coils and related gadgets.
Corona - A visible ionization phenomenon associated with high voltage. In air, corona tends to manifest itself as a blue, lavender, or purple glow surrounding an area of high potential. It's pretty, but many coilers consider corona a source of power loss and a sign of inefficiency. In a darkened room, you may see corona on almost any part of an operating Tesla coil. (The lavender glow I see inside my saltwater caps is especially neat looking.)
CRT - Cathode Ray Tube. The picture tube in a TV set, computer monitor, oscilloscope, etc. Common term for almost any high voltage image tube.
CW - Continuous Wave. The normal mode of operation for a SSTC or a VTTC, characterized by continuous, steady state oscillation as opposed to the pulsed or intermittent mode of operation found in disruptive Tesla Coils.
Disruptive Tesla Coil - Also disruptive coil. A type of Tesla Coil based on a spark gap oscillator and characterized by a pulsed or intermittent mode of operation. If there's any such thing as a "normal" Tesla coil, the disruptive coil is it.
Doorknob Cap - Also doorknob. A type of commercially manufactured, high voltage, high current capacitor popular with Tesla Coil hobbyists. The most common form of doorknob cap is a small ceramic cylinder with axial studs of brass or copper for electrical connection. However, other styles of ceramic capacitor are often referred to as doorknob caps. [click here for picture]
EMMC - Enhanced Multi-Mini Cap. A type of reduced cost MMC that requires fewer capacitors. The EMMC design is based on the fact that most commercially made pulse capacitors have a substantial built-in safety margin. The EMMC operates way inside that margin.
Energy - The ability to do work. Work is defined as exerting a force over a distance. The terms energy and power are often confused, but they are very different things. Suppose you turn on a 1000 Watt lamp for one second, then turn it off. Now turn the same lamp on for one hour. In both cases the lamp required 1 kilowatt of power. What's the difference? In the first case, the lamp expended 1 kilowatt/second of energy. In the second case, the lamp expended 1 kilowatt/hour of energy. That's a big difference! A kW/hour is enough to move your household electric utility meter one whole notch!. Let's look at another example. Suppose you have an electrical pulse which expends one Watt for one second. Now suppose we have a another electrical pulse which expends one billion Watts for one billionth of a second. Both pulses contained one Watt/second of energy, yet the second pulse was far more powerful! One last silly example. Heft a big lump of coal in one hand and a 30-06 rifle cartridge in the other hand. Which one is more powerful? Which one contains the most energy? You wouldn't try to go hunting with a lump of coal, nor would you have much luck boiling a pot of water with a rifle cartridge! See the difference? Also see power.
ESL - Effective Series Inductance. A term used to describe the internal inductive reactance of a capacitor. For coiling, low ESL is good, high ESL is bad.
ESR - Effective Series Resistance. A term used to describe the internal non-reactive resistance of a capacitor. For coiling, low ESR is good, high ESR is bad.
Fixed Electrode - The non-moving electrodes mounted on an RSG.
Flyback - Flyback transformer. A small, ferrite core, high voltage transformer found in TV sets and computer monitors. It is the main component of the high voltage power supply that provides operating potential for the picture tube. Flybacks operate at relatively high frequency (20-70kHz), and therefore cannot be powered directly by 50 or 60Hz AC line voltage. They require a special oscillator circuit called a flyback driver (go figure!) in order to operate. The flyback driver is usually some sort of transistor circuit, although it could just as well be a vacuum tube circuit. (In the early days of TV, it was always a vacuum tube circuit!) Flybacks can generate 10s of thousands of volts at up to several Watts. They can make a nice corona brush discharge, like a mini Tesla coil, and they can light up a plasma globe very nicely. Many HV experimenters start out by fooling with flybacks before moving on to real Tesla coils.[click here for picture]
Flying Electrode - The moving electrodes mounted on the rotor of an RSG.
Joule - The joule (pronounced JOOL) is the standard unit of energy in electronics and general scientific applications. One joule is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one meter. One joule is the equivalent of one watt radiated or dissipated for one second. In coiling, the joule is often used to express the size of an individual pulse or "bang" produced by the tank capacitor discharging across the spark gap. The equation applicable to coiling is: J = 0.5CV�, where J = Joules, V = charge voltage, and C = capacitance of capacitor.
k - Also k factor. A numerical expression of the coefficient of coupling between two coils. When discussing Tesla Coils, k is used almost exclusively to describe the degree of coupling between the primary and secondary coils. Perfect coupling would be k=1. Disruptive Tesla Coils require a relatively low k for proper operation, typically in the range of k=0.1 to 0.2.
Line Filter - LC noise filter placed in the 50Hz or 60Hz AC power line. Coilers use them between the power supply and the wall outlet to keep Tesla coil hash from getting into the household power lines.
LTR Cap - Larger-Than-Resonant Capacitor. A capacitor whose value is too large to allow resonant operation with a particular power supply.
Magnetron - Special type of high voltage vacuum tube used to generate microwave (radar) energy for use in microwave ovens and radar transmitters. The magnetron is very distinctive in appearance due to the presence of two large and very powerful permanent magnets mounted externally on each end of the tube's long axis. The magnetron is a diode (two element) tube containing only a cathode and a plate (anode). The cathode is the heated type, requiring a separate filament supply. The plate (anode) element is manufactured with integral vanes or hollow chambers, and is usually machined from a solid block of metal. The vanes or chambers act as tuned elements, thus determining the operating frequency of the tube, which can range up into the 10's of Gigahertz. In a typical circuit, the plate/anode is grounded, and the tube is driven with high-voltage negative DC pulses applied to the cathode. Magnetrons can be very powerful, with peak pulse outputs up into the megawatts.
Magnifier - Tesla Magnifying Transmitter. A system similar to the Tesla coil that uses three coils instead of two. The third coil, often called a resonator, plays the same role in the magnifier that the secondary does in a "classical" two coil system.[click here for picture courtesy of Bert Pool]
Mains Filter - See Line Filter.
Marx Generator - Also Marx Bank. A really neat high voltage gadget of the same vintage as the Tesla coil. In a nutshell, the Marx Generator charges up a number of high voltage capacitors in parallel, then uses spark gap switches to pulse-discharge them in series. The series cap voltages add up, yielding many times the input voltage. The Marx Generator can work like a single shot, or it can pulse a few times per second, or it can rattle off sparks like a machine gun depending on the available charging current. The Marx Generator really has very little to do with coiling. It's just such a cool gadget, I had to mention it.[click here for picture courtesy of Daniel McCauley]
MMC - Multi-Mini Cap. A type of home-built capacitor popular with Tesla Coil hobbyists. It consists of a number of small, commercially manufactured plastic film capacitors arranged in a series/parallel configuration to yield a capacitor bank of the desired voltage and capacity rating. The best MMCs are fabricated from polypropylene film & foil pulse capacitors rated 1kvdc to 3kvdc. The MMC offers performance similar to commercially built pulse capacitors but at much lower cost.
MO - Microwave Oven.
MO Cap - Microwave Oven Capacitor. Typically 0.5 to 1.2uF at ~2KVAC.
MO Diode - Microwave Oven Diode. Typically 12KV at 350-500ma.
MOT - Microwave Oven Transformer. A type of high powered, high voltage transformer sometimes employed by Tesla Coil hobbyists as an improvised power supply.
MOV - Metal Oxide Varistor. A solid state electronic component used to eliminate high voltage spikes. These are the active element in your household surge protectors. Coilers sometimes use a chain of MOVs instead of safety gaps to protect an NST or other power supply from high voltage surges and spikes created by the Tesla coil.
Nemesis - Infamous Tesla coil built by Richard Hull. One of the most well known tesla coil images on the WWW. [click here for picture]
NST - Neon Sign Transformer. A type of medium powered, high voltage transformer often employed by Tesla Coil hobbyists as a power supply.
NST Filter - An electronic filter placed on the high voltage output lines of an NST. The purpose of the NST filter is to prevent Tesla coil RF current from damaging the fragile high voltage windings on the NST. The NST filter is a lo-pass network, designed to allow low-frequency 60Hz current to pass through with very little attenuation, while blocking most RF current. The usual hobby form is an RC (resistor-capacitor) filter, with resistors in series with the high voltage lines, and capacitors in shunt to ground. However, LC (inductor-capacitor) and RCL forms are also sometimes seen. The NST filter often incorporates over-voltage protection too, in the form of safety gaps or else a network of MOVs. Perhaps the most highly developed NST filter design is the Terry Filter.
OBIT - Oil Burner Ignition Transformer. A type of low powered, high voltage transformer often employed by Tesla Coil hobbyists as a power supply. The most common type of OBIT produces 10kvac at 23ma.[click here for picture]
Oudin Coil - Special type of high frequency air core transformer capable of producing very high voltage AC discharges. The Oudin Coil is very similar to the Tesla Coil and often confused with it. However, there are significant differences in wiring, grounding, and secondary coil geometry.
PFC - Power Factor Correction. Capacitance added to the input side of an AC power transformer to improve its efficiency. The transformer presents a high inductance to the wallplug power. This causes the AC voltage and current to be out of phase. Capacitance on the input side corrects the out of phase condition. For the coiler this means fewer amps are drawn from the wallplug to acheive the same effect.
Plate Cap - Also, stacked plate cap. Plate capacitor. A type of home-built capacitor popular with Tesla Coil hobbyists. In its most common form, the plate capacitor consists of alternating layers of Aluminum foil or roof flashing and sheets of dielectric. The best plate capacitors are made using polyethylene, polypropylene, or polystyrene plastic, though other materials are often used. Window glass, Plexiglas, polycarbonate, paper, and printed circuit board stock are examples of less desirable (but serviceable) substitutes. The finished capacitor stack is usually immersed in a tank of dielectric oil to improve its performance and increase its life span. Plate capacitors tend to have fairly low ESL (that's a good thing) as compared to other types of home-built capacitors.
Plate Transformer - A type of power transformer so named because it is designed to supply high voltage (+B) to the plate element of a vacuum tube. Plate transformers are especially useful for powering VTTCs, though the higher voltage (5-8kvac) sort is sometimes used to power a disruptive Tesla coil. Large plate transformers can be quite powerful--up to a few kilowatts output.
Pole Pig - Also pig, pole transformer. Slang term for single-phase distribution transformer. Big, heavy, oil-filled, pole-mounted transformer used by utility companies to step high voltage distribution power down to 240vac/120vac for household use. Those round, barrel-like things you see on top of utility poles. An extremely powerful high voltage transformer sometimes used by Tesla Coil hobbyists as a power supply.
Power - The rate at which work is done, or the rate at which energy is transformed from one form to another. Many people confuse the terms power and energy. Something can be very powerful without being very energetic. For example, 1 billion watts expended over a period of 1 billionth of a second is very powerful, but not very energetic--it is still only 1 Watt/second! Due to their pulsed nature, disruptive tesla coils can be very powerful, yet the total energy contained in the sparks, streamers, and ohmic losses never exceeds the total energy drawn from the wall plug. Power is what gives the electronic flash unit atop your camera the ability to temporarily blind everyone in the room, even though it only has the energy content of a couple of penlight cells to drive it.
PT - Potential Transformer. A high powered, high voltage transformer sometimes employed by Tesla Coil hobbyists as a power supply. These are used in the electric power industry for instrumentation to safely measure the voltage of high-tension lines.[click here for picture]
Pulse Cap - Also pulse power capacitor. A capacitor designed to withstand very fast, high voltage, high peak current discharges. The best kind of capacitor to use in a Tesla coil tank circuit.
Quench - Also Quenching. In a disruptive-type Tesla coil, the point at which the spark gap arc extinguishes.
Quench Gap - A special type of multi-electrode static spark gap sealed in an enclosure filled with air. After a few seconds of operation, the oxygen inside the enclosure is burned away, leaving the gap to operate in a Nitrogen atmosphere (air is 80% Nitrogen). The Nitrogen atmosphere makes the gap self-quenching without the need for mechanical assistance from fans or blowers.
Reso Cap - Resonant Capacitor. A capacitor whose value is carefully selected to achieve resonant charging with a particular AC power supply.
Resonant Operation - Also resonant charging. A mode of disruptive Tesla Coil operation brought about by the use of a capacitor and transformer specially selected so as to result in 60Hz (or 50Hz) resonance --a condition that can lead to higher than normal charging voltage and current so as to realize a performance boost. See reso cap.
Resonator - Another term for the Tesla secondary coil. Also the term used for the third coil on a magnifier system.
Rotor - Disk that carries the flying electrodes of a rotary spark gap.
Rolled Poly Cap - A type of home-built capacitor popular with Tesla Coil hobbyists. In its most common form, it consists of two long conductive plates of Aluminum foil or roof flashing separated by sheets of polyethylene, polypropylene, or polystyrene plastic. The whole assembly is rolled up like a sleeping bag and slipped into a cylindrical container, which is usually filled with dielectric oil.[click here for picture]
RQG - Also RQ Gap. A special type of multi-electrode static spark gap developed by the Tesla Coil Builders of Richmond and named after TCBOR member Richard Quick.[click here for picture courtesy of Gary Lau]
RSG - Rotary Spark Gap. A type of spark gap that employs moving electrodes, usually mounted on a spinning disk or rotor.[click here for picture courtesy of John Freau]
Safety Gap - Static spark gap, normally a simple air gap, used for overvoltage protection of NSTs and other high voltage power supplies. Usually, two safety gaps are used, one from each high voltage output lead of the power supply to AC ground. Electrically, the safety gaps are located between the Tesla coil tank circuit and the HV power supply. In the event of a primary strike or other excessive voltage spike, the safety gaps are intended to arc and short the high voltage safely to ground, preventing damage to the HV power supply. Because safety gaps are only meant to fire intermittently, they are usually not as robust as the main tank circuit spark gap.
Shunted Transformer - An iron-core power transformer containing shunts. A transformer designed to limit its own current to some maximum value, even in a short-circuit condition. The key element of the shunted transformer is, of course, the shunts. These are small, rectangular stacks of transformer iron tucked into the core windows between the primary and secondary windings. Shunted transformer designs always include a gap so as to preclude metal-to-metal contact between shunt and core. This gap is sometimes established by a shim of stiff paper card stock. The shunts and shims fit into the core very tightly, and are usually cemented in place for good measure. In some NST designs, the shunts are physically part of the core on one end, but have a narrow air gap on the other end to preclude physical connection between the center and outer legs of the transformer core. Shunted transformers are useful to the coiler because they may not require the use of an external ballast. The shunted transformer seems simple, but it is actually an example of exquisite engineering to produce a transformer with such specific performance characteristics. The family of shunted transformers includes the NST, the MOT, and the OBIT. Pole transformers, PTs, and plate transformers are not shunted.
Single Static Gap - A static spark gap that employs only two electrodes firing across a single air gap.
Slide Choke - A simple type of inductive ballast often used in the neon sign trade to control the wallplug current of a bombarder transformer. The slide choke consists of several hundred turns of heavy gauge insulated copper wire wrapped around a long, hollow form, usually of square or rectangular cross section. A heavy bar of laminated transformer iron is inserted inside this form, and can slide in or out of the coil, trombone style, to increase or decrease the AC current. The slide choke should be handy for ballasting any sort of heavy-duty transformer, such as a potential transformer or a pole pig. Unfortunately, they are so rare and expensive that their usefulness to the hobby is limited.
Spark - Lightning-like electrical discharge from a Tesla coil that terminates by striking something solid.
Spark Gap Tesla Coil - See Disruptive Tesla Coil.
SRSG - Also Sync Gap; Sync Rotary. Synchronous Rotary Spark Gap. A rotary spark gap designed to present the electrodes for firing in synchronization with the 50Hz or 60Hz AC line current.
SSTC - Solid-State Tesla Coil. A Tesla Coil based on an oscillator that employs solid-state devices such as transistors.
Static Gap - Also Static Spark Gap. Any spark gap that does not employ moving or rotating electrodes.
Streamer - Lightning-like electrical discharge from a Tesla coil which terminates in mid air without touching or striking anything.
Sucker Gap - A static spark gap similar to an air blast gap in which quenching is assisted by air sucked though the electrodes, usually from an electric vacuum cleaner.[click here for picture courtesy of Gary Lau]
SWC - Saltwater Cap. A type of home-built capacitor popular with Tesla Coil hobbyists. SWCs are typically made of bottles or jars with electrolyte solution (saltwater) serving as one or both conductive plates and the wall of the jar or bottle serving as the dielectric.[click here for picture]
Tank Circuit - Also tank. Parallel resonant circuit consisting of a capacitor and an inductor. (The capacitor and the primary coil of a Tesla coil form a tank circuit.)
Terry Filter - High-performance NST filter design credited to coiler Terry Fritz. One distinguishing feature of the Terry filter schematic is the long chain of MOVs used for high voltage spike protection, in lieu of the usual safety gaps. The Terry filter has a "bulletproof" reputation. If you can afford it and absolutely must defend your NSTs at all cost, the Terry filter is for you.
Tesla Coil - Also TC; Coil. Special type of high frequency air core transformer capable of producing very high voltage AC discharges. Named after its inventor, Serbian born American Nikola Tesla.
Thyratron - A special type of gas-filled triode tube designed to switch high voltage and high current in DC pulse mode. The thyratron can handle thousands of volts at tens of amps amounting to possibly megawatts of power--but only in very short pulses! The thyratron requires an external trigger pulse to switch it on. The thyratron finds application wherever short, repeatable, high voltage, high current pulses are required, including high powered Xenon photography strobes, pulsed laser power supplies, and pulse radar modulators. You may see the term "Hydrogen thyratron" on the mailing list. This of course refers to the fill gas. However, thyratrons may be filled with other gasses including Argon, Krypton, or Deuterium. Some coilers see the thyratron as a possible substitute for the air spark gap. However, I've never seen an actual working example of a disruptive Tesla coil based on a thyratron. [click here for picture]
Toroid - Donut shaped conductor often employed as a discharge terminal on top of a Tesla coil.
Transmitting Mica Cap - A type of high voltage, high current capacitor so named because it uses mica as its dielectric, and is often employed in the plate circuit of powerful radio transmitters and amplifiers. The most common form is a short, stout cylinder with heavy-duty buss connections. Transmitting micas are sometimes used as a Tesla coil tank capacitor, where they are reported to give very good service and long life. Unfortunately, these capacitors are rare and expensive, limiting their usefulness to the hobby. [click here for picture]
TSG - Triggered Spark Gap. A type of static spark gap that employs an external high-voltage trigger pulse to control the onset of conduction.
VA - Volt Amps. Volts x Amps. The product of voltage and amperage in an AC circuit. One way of expressing power in an AC circuit. In the Tesla coil hobby, VA is often used to express power supply capability. For example, if one's power transformer is drawing 20 Amps from a 240vac outlet, the AC input power is 4800VA. VA is often confused with Watts, but they are not really the same. VA is used to express power in reactive circuits--that is, circuits that contain inductance and/or capacitance (a transformer, for example). The Watt, on the other hand, is used to express power in a pure (or nearly pure) resistive circuit (a space heater, for example). The reasons why different units of power measurement are used for reactive and resistive circuits are complicated, and beyond the scope of this glossary. If you are untrained in electrical principles and new to the hobby, it's OK to use Watts and VA interchangeably--everybody will know what you mean.
Vacuum Gap - See Sucker Gap.
Variac - A variable iron-core autotransformer which can be used to adjust AC voltage or current, depending on how it is wired. Often used by Tesla coil hobbyists to smoothly bring up the output voltage of NST based systems. Large variacs can also be used as inductive ballast on larger systems.
VTTC - Vacuum Tube Tesla Coil. A type of Tesla Coil based on a vacuum tube oscillator.[click here for a picture]
Xfmr - Transformer.