An Introduction to Tesla coils demo + talk, Derek Woodroffe (Wuthering Bytes 2019)

and the most important one on that list is i am still alive so as you'll notice i'm wearing an hv jacket this will of course protect me from all forms of hp testicles are quite dangerous not as dangerous remote controls for basic risk electrocution the obvious one in actual fact 90 percent the chance is you are not going to kill yourself you are much more likely to burn yourself but as all the doctors in the room will attest when you burn yourself and drill a little hole in yourself at the same time it cauterizes the wound this makes it less likely to heal which means you're also much more likely for infection it's the infection that will kill you explosion sounds a little weird testicles have transformers in them tester coils have capacitors in them most of which can store quite a lot of energy one magnetic the other one electrostatic some of them can be stressed quite a lot especially when you're an impoverished tester testicle and you are running them at 150 percent of their rated values not that i would ever do that at all it happens they explode i've gone through burns pretty much anybody's radiometers here anybody grabbed hold of an aerial while it's been rf a bit yeah there's a few hands going up rrf burns pleasant now i refer you back to the little holes in your fingers with wounds for you guys probably the most important thing is pacemakers and cochlear implants there isn't a huge amount of risk to be fair because these are relatively small coils but if you have cochlear implants or a pacemaker please can you stand at the back of the room i really don't want to take any risks it's really unpleasant if you pacemaker kicks in when it shouldn't have to there are a couple of other things but they are much less warnings um if you have asthma the coils that i run especially the small ones produce ozone ozone is a known irritant of the throat if you start feeling your throat going you know when you have an asthma attack get out get some fresh air you'll be absolutely fine um we've got nobody in wheelchairs have we nope okay the only other thing is if you are getting up and going anywhere especially these two here would probably survive anyway can you please either tell me that you need to go or whatever don't don't just walk into the killing zone because certainly later on we're gonna have some big spots on so why would i want to do that it's a very good question to be fair in open source and that's certainly in hopes of hardware why don't they want to do any of it um it sparks it's like fire it's fun it is it's really cool it's good stuff um it's rare as well you don't often see foot meter long spots and somebody has three or four meter long sparks in normal everyday life so there's a bit of a rarity factory it makes great entertainment it's different yeah just yeah you just don't see it for me it's the challenge um i've been an electronics engineer most of my life when i started coming into tesla coiling you know that sort of oh i know all about electronics i can holy there's a lot to learn if you think you know about a capacitor and an inductor in one circuit being fed by what is effectively a gap in a piece of wire you're wrong and i have seen university papers going on for pages and pages about how that simple thing works it's unbelievably complicated and then what you do you attach another transformer to it and an even bigger coil and another capacitor there's a lot going on but that's why i keep doing it if it was easy i had to stop ages ago because i'd be bored i ain't bored yet and the biggest thing that attracts me to me is it's dangerous yeah okay i admit it i personally think it's about as dangerous as driving a motorbike if you're sensible you're going to be safe you're probably going to stay safe some stage something is going to trip you up but if you're sensible you've probably narrowed down what is going to happen to you to the nasty burn rather than death but it's there so tesla coil there's a few examples here various different shapes be these are the smallest i've built for the old of you from the old ones of you that is of course the same icon they are roughly three inches tall they all work they produce sparks i don't know four or five millimeters something like that and then we go to the other extreme uh which is friend of mine that from the floor to ceiling is around six meters um there is a bigger coil in the uk uh which i've seen recently and i think more impressive is that's a spark gap coil this one's electronic but we'll come to that so then there's everything in between um little spark coil a little electronic coil and one i like to call flat eric for the older of you purely because i wanted to build a tesla coil that was flat and the whole of that except the battery is seven millimeters thick and i did wear it on a t-shirt until the insulation broke down interesting so tesla coiled that is the traditional circuit of terror coil one that tesla himself would recognize very briefly you have ac mains into a transformer to get it to a relatively high voltage high voltage capacitor primary coil and a secondary coil um let me show you some of those bits and here to put them into context primary coil is the four bits of brake pipe down the bottom about a thousand turns on this one and then the torus at the top um is actually another capacitor we'll come back to them how that works in a little while so that's roughly how a very simple test call sits so what happened we've got the main side 240 volts i put 10 10 kilo volts curve testicles range with the display runs between about 5 kv and about 30 kv on the primary side on our ac current charges the capacitor so over half a cycle that capacitor will charge up and we'll get roughly 10 kilo volts across it but before it gets to that point we have a spark gap the spot gap is set so that just before the capacity reaches its maximum voltage the air breaks down in the spot gap and therefore you get current going from the capacitor through the primary coil of what is essentially a transformer as we've seen we've got roughly ten turns in this case and a thousand that obviously is going to multiply the voltage up but what also happens is this is still charging it so we get the other side i have stepped over one let's go back a stage right spot gap fires that capacitor discharges through the coil it's an inductor you get an induction and a capacitor together it forms an rf circuit you just put one big pulse into an rf circuit it starts to oscillate so in actual fact it will then start pushing power back into that capacitor this will happen a number of times and the spark gap will stay conducting during that phase we've also got this secondary uh transformer here the primary secondary transformer here that will be taking what is now rf or radio frequency and multiplying it up by the turns ratio when all of that power has been pushed into the secondary and remember that that is another capacitor so that is also resonating at the same frequency of this the spark gap ceases to fire because there is no longer power in that circuit to keep it sparking of course at this point the impedance of the primary has gone from i don't know a few ohms and almost nothing that is as much an impedance transformer as it is a current and voltage transformer so strangely enough this secondary has then got a whole load of power in it and nowhere to go but you've got some lovely air and usually a little spike on the top and you can see that but most of these have got a little spike on the top you get a very high voltage and a very small spot for the high voltage to sit in so you can spark out at the top that carries on while ever there's power in the um top load and the secondary and then we're in for the next half cycle usually in main so um 10 milliseconds later and yes in the opposite direction and that is roughly how a spark gap tesla coil works it really isn't that difficult and they are actually really quite easy to build biggest problem is is actually getting hold off 10kv transformers these days used to get a lot of them from [Music] neon sign places or places that are actually of scrapping me on signs because leds have taken them out and they tend not to be as common you can still get some some stuff to do it so somebody talk a little about sport gap spark can be quite literally just two points and a gap the problem with that is we want to promote that radio frequency if your start gap stays firing all of the time you don't get a really really good rf from it you just get a big pulse so what we actually do is we use a couple of techniques this one you'll notice there's a pair of fans at either end and also we've got multiple gaps one after the other these are copper pipe and they're done so you can tap the distance that spark gap goes so we only use a couple it's about a millipiece use the whole lot it's about seven or eight mil combination of blowing air through the gap literally blows the spark out which means the rather than it's staying there and dampening that oscillation you can get a lot more efficient oscillation having multiple gaps does the same thing because if one gap fails they all fail because the current goes so it makes it a lot more likely for that to sustain a good pulse of rf the other way we can do it is with a washing machine motor a couple pulleys and what is effectively a very high speed relay not quite like a relay because these don't actually touch anything they just get very very close these flying electrodes um are usually arranged so that they connect at every half cycle in phase with the capacitor that we saw in the other diagram charging to its fullest voltage so effectively what you get is a synchronous discharge of the capacitor you can also run them asynchronous and then you get into the wonderful world of dc charging and if you're all aware arcs don't like to discharge um extinguish when you put dc on they much prefer ac so there are all sorts of ways with diodes and um inductors to quench the arc on a rotary like that and sometimes i even put a static gap in series with the rotary to again promote that that arc being extinguished capacitors usually made from lines of small caps because mark matt's a company called maxwell they sell some lovely capacitors i own a couple they are about like that they started about 500 pounds if we're doing this amateur that is the equivalent of about one half thousand pounds of maxwell capacitors made out of loads and loads and loads of really small ones we call them multi-manufacture caps mmcs and that is generally what you'll see in the bigger tesla coils purely keep costs down there is another advantage of that when you blow those up nope you can replace a few you can replace the tray it's a lot better you don't lose all the caps so it does make things a lot cheaper tesla had exactly the same problem and tesla had the money but he didn't have a company that made very very large capacitors so tesla being tesla one of the reasons i really like the guy made them happy what he did he got a tray of water add some salt to it put beer bottles in and then put a wire in the top of every beer bottle like a laden jar he had multiple trays and he even had a way of switching the trays in and out and he could fine tune it by pulling out bottles i will show you later on the size of the tesla coil that he actually did doing that and you can then think of what happens to those bit bottles one of the things i just mentioned is tuning if if we remove or add these capacitors we can actually tune parts of the coil and it is very very important that this top load on that secondary coil resonates at the same frequency as the primary coil and the other capacitor because that's where you get one maximum power transfer and two it becomes a dc sorry it becomes a resistive load as soon as you hit that double resonance you can drive it as a resistive load which makes things a lot easier come on to that later so the top load produces two main two main reasons for having it number one is um you need that capacitance and when i say capacitance that's one plate of the capacitor and as you all know capacitors need two plates the other plates is everything else in this room floor the ceiling view whatever are all that second plate to the capacitor so its size determines the capacitance the other reason for it um and i've looked the photos that prove this there are a few um it actually creates a magnetic field if you have this this doughnut shape it creates a magnetic and electrostatic field that the sparks like to follow now that is really really useful because the one thing you don't want is to start hitting your secondary coil or worse something further down but by doing that you actually make it into effectively a magnet for sparks and you think the field lines of a magnet go up and round and down that's what it does so it actually protects the secondary coil and to some extent the stuff at the bottom just by having the correct shape so that's really on top top level is for primary coil so usually 1 to 20 turns there's five on here there's about 15 on that one um these have got ten it is always around that even the really really big ones only have a few turns on their primary um it's very very high current this one as an example um that's about a six inch diameter coil and we were putting two to three thousand amps into there in rf courses which still amazes me that you can get a sheet of copper and put a thousand amps into it being driven from a transistor without blowing anything up that is an inductor it doesn't matter how small it's still an inductor i put their lowest voltage um obviously we saw the folder of about 10 kv electronic or maybe 400 volts something like that not massively high and again we can use these for tuning um you can put a crop clip or something on these and pick how many turns you have to tune coils so it's another way of tuning the resonant frequency so as i say get them to match you've got to have it to match secondary to the primary those two resonant circuits to get the best power transfer secondary coils three to two thousand turns so it's similar to similar to that one this is where the high voltage is generated they are a single layer they're a single layer purely because of insulation so you get two wires that cross over each other one you're getting point contact which isn't good two you can't guarantee that it's only one turn away from the one before so they are all single turn um very low current which actually means the output of tesla coil is generally safe apart from the rf you need somewhere in the region of 5 milliamps across your heart to do any real damage to yourself even the really really big testicles and getting up into the 10 milliamps range and i'm talking the three four foot tall one so even then unless you get it directly across very unlikely you can get home by the actual spots coming out of the top so gordon cliff one of the first and still the largest ever there is an american who is trying to um get the hat but he ain't there yet some statistics 200 kilowatts of power his primary coil was two meters tall and had two turns in it um it was a one inch diameter copper wire the secondary was um three to four meters tall i only had 100 to 150 turns which is really really low but you only need that when you've got 200 kilowatts of power and the other thing he did he actually put the top load on a long pole um i'll show you in the coil later on we can see there you see that bit there that is actually the coil and then there's a long pole going to the middle but he also had three coils all these have got two but he actually had three he thought it was more efficient um actually it's been proven mathematically makes no difference um he had one advantage though is that the third coil you can actually take away from his laboratory so all the power stuff and all the engine big expensive engineering was in a completely separate building and that is a really confusing photo because that is his laboratory that tower is about 20 foot behind the laboratory and then there is a big tube about that diameter going from his secondary coil to his tertiary coil which is the one you see there remember i said about beer bottles 200 kilowatts of power into banks of beer bottles as capacitors sparks you ought to see these photos of tesla um they're entirely done for publicity purposes he was a great great guy for doing publicity he was an engineer the last thing he wanted was sparks he was trying to transmit power and the last thing you're going to do if you're transmitting power is to make load pretty fast so who's an engineer i'll also say here this one mega volt tesla coil myth the biggest tesla coil in this country which is about four meters tall will chuck 15 foot 20 foot sparks produces about 250 000 volts where that comes from is 30 kv an inch or yeah 30kvp of retail 10 yeah 30kb centimeters that's better if you look at the length of these sparks and you take that yeah that's roughly what they look like but actually no they're not anywhere near that much um i can show you how in a little while so in fact according to that it's now okay so um i don't know how well you can see this and hopefully it's dark enough what we can do with this little coil just to produce some sparks they are a single discharge as you would get from a high voltage source at the top of there is probably 70 000 volts now if i wind this up a little this is notorious for you see those sparks are a lot bigger still the same power what i'm doing is putting multiple sparks in one after the other what you get when that happens um is you've got an ionized channel there and then the second spark takes the same ionized channel of air and that starts it that far up you got another one and another one and so with these i can actually take this up to i think 32 try again [Music] you'll also notice that all the spots coming out from that point on the end we call that a breakout and that is there for precisely that reason okay there is the protection up to top though but you know what really don't want that coming around and sparking down so we we try and keep them all coming out to the top a little little demo of a small testicle i mentioned that it was a tertiary coil i also mentioned that it was a um a spot gap coin i have a little model now this little model isn't quite true being that although there are three coils i've actually stacked them one on top of the other purely to make it easy but there are all three coils there and this model quite deliberately has a few issues with it the first one is i can't reach the bottom from that side so oh yeah this is interesting let me just run that we can get some so if we don't let it come out of the top so this is effectively how tesla had it with big cupholders at the top and some power put some power so you saw the spots coming out of the sides and coming out of everywhere which is very interesting because in the uh the photo earlier on if i put the remote down it's really confusing oh in that one there you can see sparks coming out of the top of the coil and then going everywhere now i think that that picture i know that he put a few things there but there's a there is another photo out there with it running we just start coming out of the top um i guess they're gonna take the projector out probably this one is quite deliberately slightly out of tune and it's slightly out of tune to show you what happens when you get a tesla coil that's slightly out of tune how many of you played the guitar and then we've got a couple of experts you get nodes and anti-nodes on your string don't you you press the nodes to from top to bottom is a bit like a string what you're trying to do is to get the major node to sit onto the um the breakout so you've got all the power and it's coming out of the top if you don't get it quite in tune your nose change position and you will see that about there we'll actually get a breakout and that's because it's not in tune and we're getting known from a slightly different place you'll also notice this is interesting when it comes out of there we're taking the projector out that is because it stopped being a nice rf oscillator that one frequency and it becomes old engineers tend to call squeak do you know what i mean by squeak it's like a chirp but it's rf so rather than sitting in a specific frequency they'll go up and down the range projectors obviously don't like that the other problem is as you can see this is really really fine wire you're getting spots coming out of that fine wire heats the wire up it breaks down the insulation all of those things are really really not a good thing for a tesla coil that's why i got the demo because i can show you all of those without blowing anything up so the use of tesla coils obviously tesla was trying to do power transmission laterally he decided that he wasn't going to manage to do much of our transmission the radio was quite popular at the time um so he started to try and beat marconi at his own game unfortunately he went the wrong way he decided believing tesla that the best way to transmit a long way was loads of power so all he did was he took something small and he put more and more power into it until he got sparked out of the top and he didn't get anywhere which is really annoying and he's really going for two reasons but he was so damn close and number two is that while he was doing that he was putting patents for rf transmission for um all sorts of radio frequency stuff uh methods of hearing radio waves coherence you name it he's even got a patent before and tell me what this sounds like a gas-filled tube with two electrodes one about halfway down the middle you put a voltage at either end of the tube and a speaker on the middle electrode oh a new area on my middle electrode as well yes he basically created the triode and he patented it but he didn't go that way he just wanted to put more of a power up the thing marconi admits um on record for saying that his radio uses seven of tesla's patents seven name them parts of a radio in that era which is ridiculous and tesla gave them to him does that make any sense i've never worked out why i have but it's true so the other use of testicles of that era was kind of the medical stuff i have an example admittedly this is a little beyond 200 century this is what's called the violet ray machine they are effectively a tesla coil in a handle make you apply to various parts of your anatomy yeah that is where the tesla coil is you can hear it do that and these are readily available and most of them that you will buy are absolutely lethal i'm not joking this one had a microcapacitor that had been clamped to death it was all damp and that was between live and the bottom of that tesla coil which i'm holding i have made this one safe ish please be very careful if you buy them they're great thing to play with but yeah they have some they have some real problems so yeah what really you think oh yeah i'll hand this around there is a list of the attachments can probably read someone down on the bottom right hand that i really don't suggest that kids ought to read but this is history they exist and for other places too the cure for every malibu so coming into the 1970s 1980s people started realizing that transistor technology had taken on enough and we could replace this horrible noisy spot gap with transistors so we started to replace that's our gap with transistors um and it was really really difficult to begin with to be fair uh you would be surprising how resilient the average spark gap is compared to a transistor or maybe not of course before translisters we get transistors injectors the valve tesla coil still done that's one from a couple of years ago usually beautifully built and they look the absolute biz and we've got characteristic very straight spots for those of you who are into transistors in generals that's the circuit diagram i'm afraid it doesn't mean a huge amount to me i can just about follow it effectively it's an rf oscillator anyway and then we get a bit more up to modern day certainly in the last few years our friends the chinese i say that yeah build these little kits i mean dark enough for you to see see the little spark coming out the top these are little ones you can buy for about a tenner um via ebay or whatever and they're a fully working tesla coil or even lighter fluorescent tubes cool little thing to get started in tesla coiling one word warning you can still get little burns off the top of that but to be fair you probably use the soldering iron in building them therefore you're more likely to get a worse burn off the soldering iron that one's audio modulated um parts like that very simple good start the problem with this circuit though is that it isn't really scalable um you can put bigger and bigger transistors in here and i've seen it done uh one of the big problems is you don't have a top load so you can't store a whole load of power in the secondary and also you've got no primary capacitor which means you've got to have very very small amounts of turns to keep the inductance down because you can't put any power into a high inductor not without a lot of voltage and that really gets the point so uh they're going to the solid state testicle which is kind of similar to that circuit but we can now use mains on it we're using a full bridge which obviously gives us about four times the power of a single transistor we're using power mosfets but we're still limited by the resistance of the primary the circuit very simple really some form of control which is usually on or off it might be on or off at some frequency but it is basically bridge driver current feedback that then powers your control that goes on and off so the whole of that becomes an rf oscillator fires into a bridge i think most of you know what a transistor bridge is yeah i'm going to go too too much but basically mains in drive these that way and that way into a load and there is a nice little pcb by our friends who make portable pcbs um so this one was built for steampunk exhibition so it kind of looks a little weird it also only rebuilt a few weeks ago so if it does explode i do apologize so with this we can start they're not very big because we haven't got a lot of voltage multiplication on this we still have not got that primary capacity to give us the real power but we can push [Applause] [Music] it's half an ion engine because there are actually two things one is yeah there's a big stream of ions coming out of the points there newton's third says that if you're pushing something out it'll go in the opposite direction it starts spinning the other reason why that spins is because i'm also heating the air up the hitting the air up two to three thousand degrees and the air tends to expand and go away which also produces a bit of thrust that way which one of the two is the larger i honestly don't know but it makes quite a good demonstration and electronic tesla coil just approved [Applause] [Music] [Applause] [Music] believe me we're going to the solid state testicle which is the dr sstc dr stands for dual resonant and it's purely getting that capacitor back into the circuit that we've removed because we've gone to electronics and it took quite a long time to get glue to get the electronics to that point where that could happen obviously we started off with really simple stuff start off with not particularly good transistors but we started using um igbts which really really love power and the best thing about them is their own resistance is very very low and they will oscillate at the frequencies that we want in the tesla coil um i didn't do that which are roughly speaking for these small coils about to 300 kilohertz you can even get really really big igbts which will do many thousands of amps and that is actually the biggest coil in the uk now and it's electronic it has a bridge of 2 000 igbts in the bottom of it runs at about 70 kilohertz it now it's actually better than when i took that photo um i've seen it do about four meters of spark it's very very impressive um so we've got that primary capacitor we've got feedback current control is another thing that took a long time to develop current control when you get a spot like that it's like shorting out a power supply now remember that you've got thousands of amps and hundreds of volts here and you're just going to short it out on the whim the current control became a big thing to stop the igbts from exploding and yes i said the word exploding they do i have blown the lid off so many igbts i have a shoebox full of them to keep me uh what's my g routine insulated gate pipe hold the transistor it's a musk it's a mosfet but designed for power switching sorry dart so very similar circuit you'll notice apart from the addition of the capacitor there is also another current transformer that actually does the over current detection other than that pretty much the same so that's taylor's pretty much up to date um i touched on this when i was talking about the warden clip called primary stripes you don't want your coil spark out to the top go back in to the bottom because you get some really really nasty spikes and transistors don't like spikes uh spark gap coils don't really care and that one was quite happily running with some real problems i was very proud of getting that photo two reasons number one is the coil wasn't too badly heard what he'd actually do is we've got to put the earth on so rather than that being a nice resonant to earth it was like running a guitar string that wasn't attached to the other end so it just went everywhere but really proud of that photo because i got it not only from there but in that box there is a raspberry pi also taking photos of it from still angles he didn't like it but shows the importance of earthing shows the importance of tuning in electronic coil bad feedback will do the same thing so if you imagine you've got that feedback that's trying to keep everything in phase if you use that phase you're then driving something into whatever and it just doesn't resonate anymore and remember you've got to keep it in tune with the electronic coils to keep the impedance low and make it a dc load sorry a resistive load as soon as you go away from being a resistive load your igbts are then switching not at low power anymore and they're switching at the peaks and you get a lot of heat and they're very very fast and that's when they explain that is the result of the photo you saw earlier on and these things here are called lichtenberg figures this is what happens when it goes wrong progress and will score the outside of your wonderful polished coil or in this case if you've just got a piece of insulator that isn't quite up to the task your sparks will generally progress and produce these patterns in wonderful blue peter style do you remember come and have a look at that later on here's the formula so obviously we're trying to avoid this happening trying to avoid it because in a spot to touch anything um but over time insulators do degenerate and coils will over time just explode themselves so we come to the use of tesla coils of the present day and yet they have potential high voltage transmission um a lot of the japanese now using dc to power their um long distance transmission lines and they're using tesla coil to actually get up to that dc they call it a switch mode regulator or whatever but it's an air cord transformers doesn't look another one that i see quite regularly and i've done some consulting on this personally um is using tesla coils to align carbon nanotubes during their creation and there's a cambridge university and i think it's atlanta university are looking at this at the moment um and the the name of that is called teslaphoresis well that's quite a thing um and they're making big long lines of nanotubes which obviously conduct all sorts of uses for them i'm sure but i think the biggest one for tesla cars is probably entertainment so talking about entertainment let's see if we can entertain you um yes [Music] so [Music] so [Music] so [Applause] how do we put it quite risky we'll see if this works thank you now the reason i say this risky is because i've never actually done this with these coils [Music] so [Music] so [Music] so [Music] [Applause] [Music] you