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Tesla Coils
Hi gang,
Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? thanks, p. -- "What is now proved was once only imagin'd." - William Blake, 1793. |
"Paul Burridge" wrote in message
... Hi gang, Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? They are operated in a resonant system, unlike an ordinary HV transformer. Leon |
On Sat, 27 Nov 2004 15:00:36 -0000, "Leon Heller"
wrote: "Paul Burridge" wrote in message .. . Hi gang, Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? They are operated in a resonant system, unlike an ordinary HV transformer. Thanks, Leon. Can you expand a bit? Are you suggesting that one or both windings have some sort of parallel/series/real/parasitic capacitance to bring the winding into resonance and if so, what's the purpose behind it? -- "What is now proved was once only imagin'd." - William Blake, 1793. |
The secondary and primary are resonant with each other.
The self-capacitance of the secondary is all that is required. (Compare with early Xtal sets that had an FGL, but no tuning capacitor (or condenser for those days) in evidence. "Paul Burridge" wrote in message ... Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? |
"Paul Burridge" wrote in message
... On Sat, 27 Nov 2004 15:00:36 -0000, "Leon Heller" wrote: "Paul Burridge" wrote in message . .. Hi gang, Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? They are operated in a resonant system, unlike an ordinary HV transformer. Thanks, Leon. Can you expand a bit? Are you suggesting that one or both windings have some sort of parallel/series/real/parasitic capacitance to bring the winding into resonance and if so, what's the purpose behind it? Try Googling, you'll find lots of stuff. Leon |
Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? ============================ Paul, I've never seen a Tesla coil or even recollect seeing a photo of one. But I can imagine. They are a means of generating very high voltages at relatively low radio frequencies. Low radio frequencies to minimise RF radiation losses. The coil is quite an ordinary, single-layer, solenoid, close-wound or relatively close wound in the form of a helix. Grounded at the lower end. Open circuit at the top, high-voltage end. It is coupled to the RF generator via a few turns link winding at the bottom end. Or the generator may be tapped into the bottom few turns. The working frequency is that at which the coil is self-resonant with its own distributed self-capacitance. The generator, by virtue of the number of turns on the coil and the number of the turns on the link coupling, is impedance-matched to the Q of the coil such that all the generator power is dissipated in the coil's RF resistance. This, of course, corresponds to maximum voltage at the top of the coil. The situation is identical to a short HF helical antenna without a whip on the top, operating say in the 160 or 80 metre band - but without the radiation loss. The radiation loss in the Tesla is low because its operating frequency is low. Most of the power being dissipated in the wire resistance. The theory is very simple. The coil inductance with its self-capacitance must resonate at the working frequency. The coil Q must be very high and the wire resistance must be low to generate a very high voltage. Many turns of wire are needed to resonate at LF but the wire diameter must be large enough to have a low resistance. Hence the larger the physical size of the coil the higher is the attainable voltage. The few number of turns on the link (or tap) coupling is calculable but is better determined by experiment. One will always end up by pruning to match to a particular generator impedance for maximum Tesla voltage. The coil's inductance is easily calculated from well known formlae. The coil's self-capacitance is more complicated. But what is really required is the resonant frequency. Or it can be found by experiment. (Which is what Tesla must have done.) It so happens that my program SOLNOID3 will calculate the isolated self-resonant frequency of a solenoidal coil from its dimensions. For Tesla coils dimensions will be in metres and inductances of 10's of milli-henrys. The practical design problem is insulation between adjacent coil turns. And of course the driving power. Having never seen one my instinct guides me towards a coil length to diameter ratio of 15-to-1. Have you any intentions of making one? ---- Reg, G4FGQ |
On Sat, 27 Nov 2004 13:52:07 +0000, Paul Burridge
wrote: Hi gang, Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? thanks, p. Primary coil is a tank circuit (parallel LC usually) resonant with the secondary coil. The secondary is usually placed inside the primary coil. While the primary is a parallel resonant circuit with a coil and capacitor, the secondary is just a coil and series resonant, or a coil with a large metallic body at the end to serve as a capacitor (spheres and toroids are used to minimize corona loss) A few turns of relatively large diameter wire or tubing in the primary and a lot of turns in the secondary. 6:400 turns ratio is typical enough for small systems, but that ratio isn't carved in stone. The primary is wound as a helix or spiral, the secondary is wound on a tube form, much longer than the diameter as a rule. Tuning the primary to the secondary's resonant frequency is achieved via tapping the primary coil with a movable tap. Tesla or Oudin coils can easily produce hundreds of thousands of volts. Lots of different forms and techniques are used to maximize the output voltage - that's where it gets interesting. The theory is simple - but building good coils takes experience. They can be driven with high voltage transformers and spark gaps (the most common technique) or vacuum tubes or solid state devices. They are simple to build, good for high voltage experiments, producing ozone, great visual effects, X rays, produce some RFI, etc.. There is a Tesla coil mailing list on the net that is very good. If you want to build one (and I recommend it) they can be an invaluable resource. http://www.pupman.com/ Lot of links to working tesla coils and construction ideas. Lindsay Publications www.lindsaybks.com is another source of books on the topic (among others). Lindsay reprints books published at the turn of the century (that would be the 1900's) on technology. It is fascinating reading about tesla and induction coil construction - and you can still build the stuff today with more modern materials. They did have a paper catalog of their books in print - may still have it. I built a few coils and a 1KW induction coil to drive them. |
"Reg Edwards" wrote in message ... Anyone know what differentiates a Tesla coil from any other old coil? Is it simply that they all seem to be EHT types or is there some particular quirk concerning the way they're wound? IOW, what sets 'em apart? ============================ Paul, I've never seen a Tesla coil or even recollect seeing a photo of one. But I can imagine. They are a means of generating very high voltages at relatively low radio frequencies. Low radio frequencies to minimise RF radiation losses. The coil is quite an ordinary, single-layer, solenoid, close-wound or relatively close wound in the form of a helix. Grounded at the lower end. Open circuit at the top, high-voltage end. It is coupled to the RF generator via a few turns link winding at the bottom end. Or the generator may be tapped into the bottom few turns. The working frequency is that at which the coil is self-resonant with its own distributed self-capacitance. The generator, by virtue of the number of turns on the coil and the number of the turns on the link coupling, is impedance-matched to the Q of the coil such that all the generator power is dissipated in the coil's RF resistance. This, of course, corresponds to maximum voltage at the top of the coil. The situation is identical to a short HF helical antenna without a whip on the top, operating say in the 160 or 80 metre band - but without the radiation loss. The radiation loss in the Tesla is low because its operating frequency is low. Most of the power being dissipated in the wire resistance. The theory is very simple. The coil inductance with its self-capacitance must resonate at the working frequency. The coil Q must be very high and the wire resistance must be low to generate a very high voltage. Many turns of wire are needed to resonate at LF but the wire diameter must be large enough to have a low resistance. Hence the larger the physical size of the coil the higher is the attainable voltage. The few number of turns on the link (or tap) coupling is calculable but is better determined by experiment. One will always end up by pruning to match to a particular generator impedance for maximum Tesla voltage. The coil's inductance is easily calculated from well known formlae. The coil's self-capacitance is more complicated. But what is really required is the resonant frequency. Or it can be found by experiment. (Which is what Tesla must have done.) It so happens that my program SOLNOID3 will calculate the isolated self-resonant frequency of a solenoidal coil from its dimensions. For Tesla coils dimensions will be in metres and inductances of 10's of milli-henrys. The practical design problem is insulation between adjacent coil turns. And of course the driving power. Having never seen one my instinct guides me towards a coil length to diameter ratio of 15-to-1. Have you any intentions of making one? ---- Reg, G4FGQ Of course, one must never forget Dr. Spottiswoode's 'Great induction coil'; first exhibited at a meeting of the Royal Institution held 13th of April 1877. The wound secondary was 0.01inch diameter wire, 280 miles long. Primary was 1/2 mile of 0.1 inch wire, in // with a capacitor of 126 sheets of tin foil. Powered fron 30 quarts of Grove's battery cells via a steam engine driven Brass-Ebonite-Platinum interrupter, allowing 700 to 2500 impulses a second. Generated arcs about 3.5 foot long!. regards john |
On Sat, 27 Nov 2004 19:49:48 +0000 (UTC), "Reg Edwards"
wrote: [snip science] Have you any intentions of making one? ---- Reg, G4FGQ Er, well, I ***was*** contemplating it, Reg... -- "What is now proved was once only imagin'd." - William Blake, 1793. |
Can we consider a standard car ignition coil a Tesla coil ? A cheap,
reliable and simple one. There is primary with capacitor in distributor and secondary with self resonance of course. Good high voltage insulation is achieved with coil in oil bath . Can we consider TV line transformer a Tesla coil or purely a transformer ? It is produced to resonate in selected line frequency I wonder how is normal neon light high tension generated. Do they use some kind simple tesla coil system to ionize the rare cas inside the glastubing or are they using choke like normal fluorescent tubes. In any case neon lights seem to be safe for public with very simple construction. Safety protection with fluorescent lights is much and more complicated and failsafe. New questions made Risto; OH2BT |
On Mon, 29 Nov 2004 01:44:30 +0200, "Risto Tiilikainen"
wrote: Can we consider a standard car ignition coil a Tesla coil ? A cheap, reliable and simple one. There is primary with capacitor in distributor and secondary with self resonance of course. Good high voltage insulation is achieved with coil in oil bath . A car ignition coil isn't tuned primary to secondary - Frequency is much lower than all but the largest tesla coils. Most Tesla coils are air-core transformers. Induction coils seldom put out the voltage of tesla coils. A moderate TC can output 100,000 volts compared to 20,000 for a car ignition coil. 250,000 volts isn't hard to get out of a TC. Can we consider TV line transformer a Tesla coil or purely a transformer ? It is produced to resonate in selected line frequency Flyback transformers have some of the characteristics of TC's, but usually much lower voltage, and their frequency is lower. I don't believe they are resonant - but don't know for a fact. Secondary isn't series resonant. A color CRT may go up to 50,000 volts. I wonder how is normal neon light high tension generated. They used to use current limited (magnetic shunt) line frequency transformers that relied on turns ratio to step up the voltage. Most of them still do use this type of transformer. When the gas in the tube ionizes the current limiting of the transformer protects the transformer. Do they use some kind simple tesla coil system to ionize the rare cas inside the glastubing or are they using choke like normal fluorescent tubes. The more modern neon sign systems do use high frequency/ high voltage generators because they are cheaper, smaller, lighter, and safer. In any case neon lights seem to be safe for public with very simple construction. Neon signs and neon sign transformers aren't all that safe. Many are current limited below the ~100 ma necessary to kill (but 100 ma is just a number; they didn't arrive at it empirically . . .) Look at the controversy surrounding taser weapons - much lower average current and power than a NST. Safety protection with fluorescent lights is much and more complicated and failsafe. The ordinary magnetic ballast fluorescent lamps have the usual line voltage hazards. I wouldn't consider them any safer than incandescent lamps. High frequency fluorescent lamps may be somewhat better - but the one I just took apart does not have line voltage isolation. Looks like they just rectify the AC line than chop it at a high frequency and use a small choke to limit current. Fail safe? How do you figure? New questions made Risto; OH2BT |
Fail safe? How do you figure? Thanks for your comments to the various questions. Maybe my English impression was poor. With fail safe I was meaning the safe construction which is controlled by regulations and paragraphs. In outdoor use and in moist places standard fluorescent tubes, their wiring, chokes and igniter are never allowed to have open construction. (at least here in Nordic countries) Similar situation is not with neon lights on the walls. Sometimes there are bare without any enclosures. I even remember having seen the end wires of the tubes visible. Well - normally neon lights are rather high so that people cannot touch them. Risto |
On Thu, 2 Dec 2004 00:27:15 +0200, "Risto Tiilikainen"
wrote: Fail safe? How do you figure? Thanks for your comments to the various questions. Maybe my English impression was poor. With fail safe I was meaning the safe construction which is controlled by regulations and paragraphs. In outdoor use and in moist places standard fluorescent tubes, their wiring, chokes and igniter are never allowed to have open construction. (at least here in Nordic countries) Similar situation is not with neon lights on the walls. Sometimes there are bare without any enclosures. I even remember having seen the end wires of the tubes visible. Well - normally neon lights are rather high so that people cannot touch them. Risto Interesting. I'd probably call what you refer to as "fail safe" as "foolproof." Do you have stricter regulations regarding fluorescent lamps versus other line operated electrical appliances? Perhaps the reason for stricter controls is the fact that fluorescent lamps are frequently used in family residences. Or, perhaps they are concerned about electromagnetic fields - here it is politically unpopular to even hint that low frequency emf's can be damaging to health. I've read that some Scandinavian countries are considering imposing LF EMF limits or are already doing so. Do you know anything about that? I see the same things with neon tubes here, particularly in the older establishments. Wires with just a plastic or glass sleeve over the connection to the tubes and not protected from water or hands. The transformers usually have a secondary center tap that is grounded, so each side of the neon tube only sees half the total high voltage. But half is still a lot . . . My smaller transformer is 10 KV @ 30 ma (for ignition on an oil furnace - but identical in construction to a NST). I can't imagine it feels good if one were to get body parts across it. It is designed to start fires . . . I'm not about to try it and I don't know anyone who got shocked by one. One correction to my earlier post: The common style of car ignition transformer relies on a rapidly collapsing magnetic field to produce a spike of high voltage, not just the turns ratio. Field builds slowly and collapses fast. If the same induction coil were used with a capacitive discharge ignition circuit, the turns ratio and high primary voltage produces the high voltage. |
The essential difference between a Tesla coil and all the others, such as
ignition coils, is that the Tesla coil is designed to makes full use of a high coil Q. Coil Q = Coil Reactance / resistance. i.e., it makes use of the resonant rise in volts across a tuned circuit with high inductance, low (self) capacitance and low resistance. It has to be physically large to obtain a low wire resistance combined with a high inductance of many turns. In addition, of course, the large physical size enables very high voltages without flash-over. Optimum resonant frequencies (very non-critical) for home constructors are between 50 and 150 KHz. The lower the frequency the higher the voltage. Use a ball or a thick ring on the top to minimise corona discharge. It's as simple as that. I hope this description will enable you to make your own Tesla coils. But in this day and age they are mainly of educational and entertainment value. Perhaps they always were. Tesla was a flashing-light with bangs, circus showman without knowing exactly what he was doing. Ingenious nevertheless. But perhaps not quite in the same class as Edison. Even Edison and people like Marconi did not know exactly what they were about. But we should be very grateful to the few workers, the willing slaves of technology, between 1880 and 1905 who dragged the human race, often at great personal disadvantage and expense to themselves, away from the feudal age into the present age of electronics. The $64,000 question : what is the human race, you stupid set of succeeding genocidal suckers, to do with your rich inheritance? Too late to ask Tesla. ---- Reg, G4FGQ |
On Sat, 4 Dec 2004 19:09:59 +0000 (UTC), "Reg Edwards"
wrote: It's as simple as that. I hope this description will enable you to make your own Tesla coils. But in this day and age they are mainly of educational and entertainment value. Perhaps they always were. Tesla was a flashing-light with bangs, circus showman without knowing exactly what he was doing. Tesla was a genius cruising through life, having fun, without caring or worrying about the ramifications of his toys. Ingenious nevertheless. But perhaps not quite in the same class as Edison. Even Edison and people like Marconi did not know exactly what they were about. Not in Edison's class. A class an order of magnitude above Edison perhaps. Edison and Marconi were more interested in profiting from their inventions (or their refinements of the inventions of others). They can be honored for their commercialization of inventions and bringing the ideas out of the laboratory. Thomas Edison had a lot in common with Bill Gates in that respect. Tesla probably understood his inventions better - to his way of thinking the induction motor and three phase power were so obvious they didn't warrant much discussion or interest. But we should be very grateful to the few workers, the willing slaves of technology, between 1880 and 1905 who dragged the human race, often at great personal disadvantage and expense to themselves, away from the feudal age into the present age of electronics. The $64,000 question : what is the human race, you stupid set of succeeding genocidal suckers, to do with your rich inheritance? Many of us fall into ruts and become worker bees. From birth we are programmed to seek safe secure ruts . . . Some of us just cruise through life. The "successful" apply the efforts of others. Little is done with the "betterment of mankind" as its real justification. Humans just continue to react/respond to the conditioning of millions of years of evolution. We can see that something better should or could be done with what we have. But we don't. All of our flaws and gifts are what enabled us to survive. We still play those cards - even though we changed the game substantially in the last 4,000 years. Too late to ask Tesla. Now that would be interesting. Reg, G4FGQ Playing with Tesla coils has been very educational and has altered my perspective a great deal. For instance, I groked the concept of SWR with a detached cerebral understanding until I saw it in a Tesla coil. Ditto harmonics. I understood that inductance is related to the square of the turns, but it was so much book learning until I built an induction coil. Likewise I thought the 1600's to 1900's were the dark ages scientifically - then I read some of the old masters and realized that they were very smart cookies. They had to deal with concepts that they didn't have the language to describe, yet they still understood what was happening. They frequently resorted to mechanical models in an attempt to make it physical and understandable. Imagine what they could do with the oscilloscope I take for granted. I rank Hertz, Gilbert, Maxwell, Kelvin and Tesla among the gods, and Edison and Marconi among the mortals. And . . . if you go back just a few more millennia, the inventors of musical instruments were dealing with the same concepts that Tesla and Marconi were playing with. Likewise the first engineers trying to manage crop irrigation or heat a bath. Doubtless they were equally brilliant; they just didn't have the base to build on. |
On Sat, 4 Dec 2004 19:09:59 +0000 (UTC), "Reg Edwards"
wrote: The $64,000 question : what is the human race, you stupid set of succeeding genocidal suckers, to do with your rich inheritance? Pass it on down to the next generation of suckers, Reg. Haven't you noticed the pattern? It's been going on for *quite* a while... -- "What is now proved was once only imagin'd." - William Blake, 1793. |
In article ,
says... Ingenious nevertheless. But perhaps not quite in the same class as Edison. Yeah, that must be why the SI unit of magnetic flux density is abbreviated 'E', for 'Edison'. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
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