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Music, Magic and Mayhem with Tesla Coil

Tesla coil is not all about big and loud sparks:

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See? Tesla coils can be very quiet, or musical! Isnt that strange? I always thought an arc makes a big sound. But the noisy ones onlymake big sound because they have low frequency components in them.

If you dont care about the circuit and want some answers to what you saw in the video, skip all the way down to Explaining VideoScenes.

Posted on May 26, 2015

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But before I elaborate on the circuit:

IMPORTANT SAFETY NOTES:

Death is close by, try to prevent it!The radiation from this device can easily interfere with electronic devices, like pace makers. be very careful. All my touch screenswere messed up being within a meter of the coil.This circuit can burn your skin badly (see picture at the end)

If you go back and read my Slayer Exciter article, there I explained that it is made of two windings, a primary with very few turns (around10), and a secondary with many turns (around 1000 and above). But what you should know is that every inductor has a stray capacitivecomponent and every capacitor has a stray inductive component.

For the secondary we intentionally increase the capacitance by adding the top load (the toroid on the top) which crease capacitance tothe surrounding material.

This capacitance and secondary inductance create a sharp resonance frequency, which is very sharp! It basically means that only at thatresonance frequency you will have a virtually infinite impedance, where all the energy can be radiated in the surrounding world.

That frequency is :

Where f is frequency, L is the inductance and C is the capacitance.

Now for the primary to be able to transfer the maximum power to the secondary and radiate it to the air, primary must also oscillate atthe same exact frequency. In old time Tesla coils or spark gap type in general, a capacitance is also added on the primary side that istuned to resonate with the primary inductance at the same exact frequency. You see the spark gap type driver below. It is still a verypractical method when you need to make extremely large voltages.

Tesla Coil and Solid State Driver


In this type, the AC power input which is typically at 50Hz or 60Hz is amplified by a transformer to thousands of volts, which charges thehigh voltage (HV) capacitive. In every cycle of the AC, the capacitor voltage reaches very high voltage twice (negative and positivepeaks),which is enough to break through the spark gap. The ionized air of the spark gap shorts air, and the HV capacitor to the primaryof the Tesla coil. Now the capacitor is across the primary which will oscillate at the secondary resonance frequency, transferring all thatenergy and creates a super huge voltage on the output of secondary.

The super loud noise of this type is simply because you have a lightening every 100Hz or 120Hz.

Having a solid state driver, like a slayer exciter or the one I explain below, you can run your circuit continuously at the resonancefrequency using the fast circuitry that can oscillate at coils resonance frequency. Below is the schematic of the circuit I designed.

This circuit takes two input supplies, one at 12V at J1 connector, for which I used a 12V wall adapter, and VSUP, which I used my labpower supply at 32V for this video. You can also make the 12V from VSUP using an on board inverter. Originally I wanted to use my FullBridge Rectifier and run VSUP at 170VDC rectifying the 120VAC. But that voltage was too big for my circuit and for the reasons I alsoexplained in my Tesla Coil Half Way Report my MOSFETs (Q1 to Q4) blew up. I have plans to get around the issue but for now Idiscovered much beauty even at lower powers!

This is one of the ways Tesla did it


Heres the Bill of Material for my circuit:

R1 and R4: 1k OhmR2 and R3: 10k OhmR5: 100 OhmR6: 2.7 OhmPOT1: 1-1623849-0 (multi-turn trim potentiometer)POT2: any single turn 100k potentiometerC1 and C4: 100uF, >16VC2 and C5: 10uF, >16VC3, C6 and C8: 100nF, >16VC7: 100pF, >10VL1: 10uH, >2AU1: MC78L05BP-AP or similar 7805 5V regulatorU2 and U3: MCP6562-E/SN (dual comparator in one package)U4: MIC4452YN (MOSFET driver IC)Q1 to Q4: SCT2450KEC (Power MOSFET, 10A, 1200V)

This circuit is pretty simple. The 5V supply is created by U1 that feeds the low power comparator and OpAmp circuits.

The 12V supply is separately filtered through L1 and capacitor to supply U4, the MOSFET gate driver. The reason is that this driver drawslarge current spikes to quickly drive the MOSFET gate capacitors and the noise on the supply can easily effect the oscillator circuit,while we need an accurate frequency. It is also important to pay attention to the ground routing. Make sure the ground for the oscillatorcircuit is not supplied through power circuits (MOSFETs, gate driver).

U2 circuit is an Schmitt trigger oscillator circuit. Its frequency can be tuned somewhere between 500kHz to 1.5MHz using the POT1potentiometer. My Tesla coil resonance frequency is around 1MHz. The output of the oscillator circuit where Ive taken it from thecapacitor C7 is a saw tooth waveform. I did it intentionally because I wanted to create a variable duty cycle PWM signal. So I comparethe saw tooth signal with a DC voltage created by POT2. Depending on the level of the DC voltage, the duty cycle of the PWM can betuned. Below is how the PWM changes by the DC level compared to saw tooth signal (click to make it move). This is similar circuit Iused in Making an Electric Tooth Brush. Just that my PWM signal is inverted to what you see below. I didnt want to remake this gif justfor an inverted signal!

Solid State Tesla Coil Driver


Now the PWM goes through U4 gate driver which will switch MOSFET transistors Q1 to Q4 on/off. I used 4 transistors so that they canshare power between them and dont get too hot. I also mounted them on a heat sink because they get quite hot.

Now when MOSFETs turn on, the primary is charged with current and when they turn off, the energy converts into a large voltage spikeon primary that generates large voltages on secondary. The arcs are very quiet, like I mentioned and you seen in the video.

Important Functional Notes:

Very important! Dont use metal a screw driver to tune your circuit. It may burn your finger and it will mess up your frequency. Use aplastic or wooden, rather long screw driver. I carved my screw driver from a long stick.The arcs will not jump out directly from the toroid as it still doesnt have mega volt levels. You need to simply place a rod or somemetal with a sharp tip so arc can jump out of it.You need to accurately tune the frequency for the arcs to come out. But every coil has its own resonance frequency. To find what itis, make the simple Slayer Exciter circuit. When your coil works well with the exciter, probe the base of the transistor with a scopeand measure the frequency and voila! you know the resonance frequency.The resonance frequency can greatly change based on the environment around the coil. For example if you bring your hand close,or place different objects around it, the stray capacitance will change, changing the resonance frequency. This circuit, unlike theSlayer Exciter, doesnt have a feedback to automatically tune the change. So if you change something, re-tune the frequency to getbiggest arc. For example in my video, for every scene I had to re-tune it based on what I was bringing close to the toroid. It will beclose to the original frequency though, so turning POT1 back and forth a bit, you will find the peak.For maximum power, tune the PWM duty cycle to 50% to 60%. Above or below this duty cycle will not yield any more power.Before applying VSUP, turn the 12V supply on, make sure all your circuit works, tune the frequency to what the resonance issupposed to b. Then turn VSUP on at a lower level and tune your arcs a bit, then ramp it up to maximum (32V in my case). Thentune the frequency further (very slowly) to get the arcs going best.Dont run the circuit for too long as the MOSFETs will get quite hot and can burn, killing R6 and U4 with them. A good heat sink isimportant.On that note, buy many spare parts!VSUP can be further increased. I have tried 45V also and my arcs get bigger. I have also tried 170VDC from my bridge rectifier withlarge arcs. But it is on the edge of destruction there. If you have an auto transformer, you can tune down the AC supply to yourbridge to protect the FETs but yet get bigger arcs. The reason they break at higher voltages is that when the MOSFETs turn off, theprimary voltage jumps high. If it goes above the 1200V rating of the FETs, they enter avalanche mode and get very hot andeventually break. Great heat sinking is key.The arcs may get noisier at higher power because they will start loading the supplies and VSUP wouldnt be a nice and clean DC,creating noise at the output.POT2: something you should note that U4 has a strange behavior. When the input PWM duty cycle goes below some value around10%, the output of U4 actually generates bigger PWM and can jump close to 100%. That is not good. So make sure you knowwhat that level is on your potentiometer and not go below it. You can add a 15V series resistor between your POT and ground.Thats what I used and it ensures the DC voltage doesnt go too low.One more important thing, make sure physical bottom side of both windings are connected to DC levels (primary bottom to VSUP,secondary bottom to ground or VSUP). If you do it another way, you may get weaker sparks.I connected the primary to my circuit using alligator clips as shown in picture below. The red wire is VSUP and the black wire iscoming from the MOSFETs. Moving the black wire can change the number of primary turns. You can increase the size of your arcby tuning the black wire location.

PWM Signal generated by comparing a sawtooth wave with a DC level (click to see animation)


You might ask why I didnt use a feedback like the slayer exciter circuit to auto tune the resonance frequency. It was because I wantedto make high quality audio, which was very simply done with this circuit. Having audio is also possible with the auto-tuned circuit, but youwill get saturated sounds with that one, not a nice music like this one with such simple circuit, unless you want to get fancy with yourdriving circuit. Heres a snapshot of the circuit:

Making the Most Dangerous Speaker

Now I moved POT2 and placed an OpAmp Circuit shown in picture below. J2 is an audio jack, or in my case I just cut a brokenheadphone cord and soldered it to my circuit. I could plug the jack to my cellphone or laptop.

U5 circuit basically amplifies the audio, with a gain tunable with POT3. POT2 still has the same effect as before. It tunes the averageduty cycle while the audio input modulated the duty cycle with audio signals around the average PWM. The change in PWM creates achange in output power of arcs and so creates sound.

Primary Connections of the Tesla Coil

Tesla Coil Solid State Driver Circuit


Heres the Bill of Material for new components:

U5: Any standard OpAmp with an output that can reach zero would work. I used LM358.POT3: Same at POT1, multi-turn potentiometerR7: 1k OhmR8: 10k OhmC9: 10uF >10V

Now this is some manly speaker! Why would anyone create sound using a diaphragm when you can use arcs instead?!

Explaining Video Scenes:

Yes, the arcs are very quite like I explained. This is especially great because it means you can play music with it without too muchbackground noise.When you bring a florescent light close, it turns on. The super high voltage excites the florescent material in the lamp like Iexplained in Slayer Exciter video.Using the incandescent light is pretty cool. You can see the plasma made in the lamp and the flow of electrons like dancing flames.The special form of plasma in the bulb is due to the gas in it. As you see in the video as soon as the glass melts and breaks underthe extreme heat of the arcs, regular air gets inside and the arcs look the same as ones in the air.Of course the glass is non conductive. What you should remember is that there is no continuous one way flow of electrons. Thearcs you see are electrons jumping back and forth at 1MHz frequency. This means that at that high of a voltage we just have acapacitor between the toroid and the light bulb contacts attached to my hand. The capacitor insulation is air and glass. In every1MHz cycle, the electrons jump to the glass pushing the electrons inside the bulb away, and then the toroid sucks them back inleaving positive charge at the glass, which will pull the electrons into the bulb, and thats the flow of electrons creating the plasma.There are no electrons passing the glass, of course until it breaks.My spinning wheel, it was beautiful! Theres a jet of electrons shooting from the ends, of course, but it is not the weight of electronsjumping out that turn the wheel, no siree! The mass of electrons is almost zero. And they are not jumping out anyways, they arejumping out and in at 1MHz frequency. So what is turning the wheel? It is the expansion of air due to the heat of arcs that pushesthe rod away. The arcs are pretty hot. In fact when I bring my hand close to them, I can feel the heat rising from them.The arcs dont zap like regular electricity. Yes, that surprises me too. It has something to do with the no noise nature of these arcs

Tesla Coil Solid State Driver with Audio


too. If arcs make noise, they are much more dangerous! Why? Two reasons: first, at such high frequencies like 1MHz, your nervesor muscles dont react to the electricity, so you wont shake or jump. But it is not really the reason why they are less dangerous.Second: they are less dangerous because of something called Skin Effect, which is not about human skin, but rather conductorsurface (skin). Look it up. Basically as the frequency rises, electromagnetic fields are created in a conductor that push the flow ofcurrent to the surface of the conductor in a thinner skin, and less is passed through the central area of the conductor. Thats calledskin effect. For 1MHz, the most of current can only penetrate around 60 micro-meter deep into a conductor. For a human, it meansit will no go deep enough to effect vital organs like brain or hurt and remains on the surface of body. The arcs that make noise havelow frequency components in them in audible range. These frequencies can penetrate deeper in the body, shake muscles and belethal.The arcs, jumping directly to the finger, burn the skin black. See my picture below for burns from all that testing. The reason is thatthe arcs enter a small spot and all that energy through a single spot makes a localized hot spot burning the skin. Another reason isthat the skin is made of dead non-conductive cells. So when the arcs pass through such high resistance layer, they create a lot ofheat and burn it. As soon as electricity reaches conductive tissues, it disperses around to larger surfaces that generate much lessheat.But why doesnt it hurt when I hold a metal in my hand and touch the arcs with it? Because the metal provides a greater surface tomy hand and rather than a spot, there is a bigger area for electrons to move into my hand. So the heat dissipates on a biggersurface rather than a spot and doesnt burn anymore. Also when I hold the metal, I put a pressure which makes the non-conductiveskin thinner and less resistive. But if I touch the same metal at a single point with not much pressure, it burns my skin.Why do the arcs jump to a floating metal object like my screw driver? Simple! It is not like they jump to the screw driver to jumpsomewhere else. Screw driver is like another plate of a capacitor, which has a tiny bucket of charges in it. So what the coil does isthat it sucks out and pushes back in that tiny amount of charge away/to the screw driver.Even when the arcs are not jumping to the screw driver it zaps my finger. Screw driver, just being close enough to the coil, peaksup electric fields, like another plate of a capacitor. Those fields are so strong that they can suck/push charges from my finger.I love the audio I created. I showed you two tuning of the circuit, one that sounded nice and smooth, and the other which soundedsaturated and jumpy. For the smooth one, you have to raise the PWM to around 50% and reduce the audio gain to prevent anysaturation of PWM signal. For the saturated one, you have to lower the PWM so much that arcs dont jump. But then raise the gainso much that the PWM level can jump to 50% or 60% or more. That way the low level audio doesnt pop out, but usually the basswhich is a higher pop pushes a high PWM and causes the arcs to jump. And the arcs created this way can jump further too.The popping arcs from my saturated audio jump much further and sharper than the fuzzy arcs of the smooth flow. I believe thereason is that when the arcs are continuous and consistent in level, the air all around the pin is ionized and the energy flows inevery direction continuously like you see. This makes the arcs shorter too as they are not focused anymore. But when they pop outin single bursts, the air has time to create only one ionized channel and all energy flows through there. So it jumps further.

Now if you wonder how my skin looks like after so much burning, here it is. All those burns were surface deep and the black burns couldbe washed away, although they left small blisters here and there, because, well, they were hot! Dont burn yourselves! and DO YOUREALLY KNOW HOW I GOT THOSE BURNS?!

You may thing I got them from touching the coil. Half of them maybe, but the other half was from touching metals around me, or turningthe damn camera on/off! Every time I tried to touch something while the coil was running, it would burn me. Just sitting close to the coil,my body would peak up enough energy to zap any metal I touched, same as touching the screw driver in the video. Almost ten times Iforgot to turn the coil off, while tried to turn the camera off and saw smoke coming from my hand and camera. Fortunately the camerawas not damaged.

My finger burns from Tesla Coil


And more shots of my beautiful coil:

Tesla Coil with Solid State Driver


11 THOUGHTS ON MUSIC, MAGIC AND MAYHEM WITH TESLA COIL

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This entry was posted in Electricity and tagged amplifier, arcs, audio, audio amplifier, audio output, burn, coil, driver, electricity, electroboom,electronics, florescence, florescent, high current, high voltage, low noise, magic, mehdi, mehdi sadaghdar, mosfet, mozart, music, OpAmp,plasma, playing mozart, power, resistor, resonance, sadaghdar, shock, skin effect, solid state, sound, spark, speaker, stray, straycapacitor, tesla, tesla coil, top load, transformer by Mehdi S.. Bookmark the permalink.

Tesla Coil with Solid State Driver

Omar Zupial on May 27, 2015 at 4:15 pm said:You should play your ending beatbox music with the arcs, that would give the final touches to your eyebrow dance and it wouldawesome.

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JOHN.T.DICKENS on May 27, 2015 at 8:54 am said:click on my website link and youll see how you can use this kinda technics to make SUPERB fascinating pictures without theuse of a camera,lens or filter !all films can be used : 66 or 2436 or larger professional film.positive,negative,colourslides,infra-red or whatever material you canget your hands on.all working have to be done in absolute dark since you have to take all the films out of their cassette to exposethem.the room/place should be ventilated since OZON is a byproduct and you should wear isolating footwear to avoid that a sparkmakes contact with earth by your toes or part of your foot.every serious email reaction is welcome :))

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stephen on May 27, 2015 at 1:11 am said:How many wraps and what gauge does your coil consist of?

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Nikola oneTesla on May 26, 2015 at 9:20 pm said:superscratchy, depending on what kind of coil you have, you could use the SD MIDI interrupter kit available at our website.

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Mehdi S.on May 26, 2015 at 11:42 pm said:

I tend to make things from scratch to see how they really work. But thanks!Also the interrupted creates a digital saturated sound, not a clear music like the one I made. But I may use that scheme ifI want a higher power coil.

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Nikola oneTeslaon May 27, 2015 at 12:00 am said:

Theres definitely something to be said for designing something from scratch! Full-spectrum audio coils (like yours)and DRSSTCs (big sparks, few notes) are different topologies, anyway, so our interrupter wouldnt be useful for thiscoil. Try a oneTesla kit for your next project, its sure not to disappoint

You may enjoy this shady tinyTesla: https://www.youtube.com/watch?v=jyufWbqCkhM

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Daylon Moores on May 26, 2015 at 8:39 pm said:This is really cool! I like it when the two sides sparks and spinning really fast! how fast is this?

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Not too fast! maybe 1 revolution per second.

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superscratchy on May 26, 2015 at 7:25 pm said:Id love to hook my coil up to some sort of sound input to modulate the arc. I cringed when you plugged your driver into the laptop.I dont see any opto-couplers in your diagram. What are the chances of HV finding its way back into my laptop and killing it?

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Depends on the power of your coil. If the arc is long and gets to your circuit, you are doomed! You could plug it to yourcellphone that doesnt have an earth connection. Just that the cellphone touchscreen wouldnt work due to high radiation.You have to setup your cellphone and then start your coil.opto coupler is your safest bet of course!

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