Active 5 years, 2 months ago. Viewed 10k times. How they can calculate what tone it is going to do? And what are the factors to consider?
Improve this question. F'x 1, 12 12 silver badges 33 33 bronze badges. Garmen Garmen 1, 4 4 gold badges 15 15 silver badges 29 29 bronze badges. Nifty instrument, that. It's fun and a sure fire way to impress anybody and make them think you're cool. Add a comment. Active Oldest Votes. And in , he and his brother did just that. It was a pivotal moment in the industry. Until that point, Tesla coils were exclusively used for visual and educational purposes.
Of course, every hobby has that group of people dedicated to doing things a certain way, DiPrima says. I get it. Ever since the fateful day in , DiPrima has toured his musical Tesla coil around the world. So far it seems fairly simple, but the complexity comes in when we see that this is an LRC inductor - resistor - capacitor circuit, loosely coupled with another LRC circuit. Because it's loosely coupled not all the energy is passed per cycle.
What's more is we want to be able to pass as much energy per cycle as possible - and this can be done by energizing the primary coil at the resonant frequency of the secondary. Before I explain how we calculate the resonant frequency see the step regarding the secondary coil , I'll explain what resonance actually is.
I would highly recommend visiting Richie Burnett site - he explains in a lot more detail how Tesla Coils work and he really gets down and dirty with the math - he also includes a lot of 'scope traces to further back up the theory, a must read for Tesla Coil enthusiasts! Resonance is key to building a Tesla Coil that makes large sparks - without it you'll be lucky to see anything although you may still hear it!
So what is it? Resonance is a natural phenomenon that basically means you can provide energy at a certain period or frequency to something that's currently oscillating and even though you're providing the same energy each time, the amplitude of the oscillation gets higher and higher. The best example I can give of this is with a swing, When you push someone on a swing you normally wait until they have swung all the way back and briefly stopping until they continue there swing and forwards - this is the point you push them.
You're providing energy to the system at regular intervals and the person is getting higher and higher. To further this analogy and tailor it slightly more to Tesla Coils imagine that when the person on the swing reaches a certain height they jump off and land on some grass somewhere.
We can't give one single push straight away for them to reach this height, we're just not that strong! But after a few pushes or oscillations they're high enough to jump! This is how Tesla coils work, we run them at the resonant frequency to top the voltage up on the top load quickly and with little effort until it becomes so high it ionizes the air and causes sparks! That's pretty much it!. Continuing with this example, if we push them when they're just after the halfway point of they're swing, we going to need a lot of force and all we'll do is slow them down.
This is similar to you running your Tesla Coil out of resonance and you're likely to draw too much current and blow something in the circuit.
I should mention here that my design is slightly different to most in the sense that I haven't used a normal micro-controller, I've used the National Instruments myRIO - a great piece of kit that allows me to control the Tesla Coil wirelessly due to a built in wireless adapter and have deterministic switching using it's real-time operating system and on-board FPGA.
This meant I could have a pretty cool user interface and perform FFTs on an audio signal to obtain it's frequency - I understand not everyone has access to this so I'd advise something like the STM32F4 Discovery board as an alternative. Now, lets talk circuits! Please note my design was based off Steve Wards see the final image , I made a few alterations to this to suit my needs. Please check out Steve's site, he's a member of the infamous ArkAttack and he really knows his stuff!
An interrupter does what it says on the tin and simply interrupts the signal, giving the TC a rest. This makes it a lot easier to solder together, I did make some prototypes on strip board but after the 3rd one exploding I decided against it :P. As far as I'm aware all of the SSTC use the same idea of either a half bridge or full bridge of transistors to switch the current through the primary coil.
I used a half bridge because it's cheaper, you only need two IGBTs rather than 4 and so I'll talk about that one instead of the full bridge. From the image you can see that the rectified DC voltage is on the top rail and we have our two IGBTs and finally a terminal block where we connect our primary coil. As well as this we have two high voltage PP capacitors. It seems that we need to hold one end of the primary coil between the two rails so that we can pass the current through it either way when we're switching.
Of course, if we just connected it without these capacitors, we would short the power rails. Hence, the capacitors simply act as a DC decoupler. But it comes at a price, because of this we end up with a potential divider and half the available voltage we can switch across the primary. Most people I believe in the US incorporate a voltage doubler circuit, but I didn't feel the need since the US use V, half of the UK already, therefore I would be switching the same voltage as them without a doubler circuit.
See the hardware list at the end for the components I used, really the IGBTs you use don't matter, so long as the peak pulsed current is high enough and the voltage is high enough. Usually, the voltage is the easy one - the higher the current you want the more you'll pay! These are very important for the TC and I'll explain why. It's no surprise that these don't instantly switch, they take a finite amount of time. There's now 3 states that the switches can be in; both on, both off, or complimentary of each other.
We always want to know the state of the switches, and so you never switch them both at the same time and so we introduce what's called dead-time. So option 1 is a no-no. Option 2 is to have them both off, well if we do that we can't short out the supply voltage right? True, but we've also got an inductive component that's storing a lot of energy and now has no path to ground.
Eventually it'll find a path to ground which usually results in a spark which can go anywhere and damage anything. Another no-no. Finally, option 3, switch them at exactly the same time and hope for the best - hmmm maybe not.
What do we do!? The answer is, option 2 BUT, we add in flyback diodes to give that energy stored in the coil a path to ground. So those diodes are very important! The reason we need this is that most micro-controllers have 3v logic - that is they can only provide 3v when their outputs are high.
This isn't nearly enough to fully switch the gates on the IGBTs, nor do they supply anywhere near enough current to turn them on quickly. With my design I don't need very large heat-sinks because they don't get very hot due to the speed in which they switch.
I found this link here that explains the IR extremely well and why you need the bootstrap capacitors. Essentially you provide your switching signal to the input of the IR - this comes from the uC micro-controller or in my case, the myRIO. It then steps up the voltage and essentially amplifies the current. What's great about this chip is that it has a shut-down pin, meaning we can control when the spark occurs.
In the second image you can see the response from the IGBTs switching, there is a fair amount of ringing on the signals, this is the reason for the 5ohm resistors on the outputs of the IR, it reduces the ringing but it does increase the time taken to switch - so it's a bit of a trade-off. What happens is we produce a two square waves at the resonant frequency of the TC degrees out of phase of each other and input them into the corresponding high side or low side input.
This will then amplify the voltage and current and switch the IGBTs nanoseconds later and hence energize the primary coil. This is also what allows us to play music more on that later. As I mentioned before, we need a DC voltage to energize the coil. Via: ArcAttack Music 2. Start trying something new right now!
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