Tesla coil driver idea, please fact check me - Page 1
Forum section: electronics / beginners

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: January 09, 2020, 05:30:00 pm
content: I have come up with a hybrid SSTC-SGTC (which I call a Solid State Spark Gap Tesla Coil, or SSSGTC) driver idea, but I do not want to build it until I get the facts 100% straight. Basically, to prevent it going *crackle, pop, boom.* I need to make sure that I can make this circuit as efficient as I can so I don’t consume huge amounts of power with the driver. In case you can’t read the sloppy handwriting, I will write the text version here:Multivibrator is actually a 556 timer, to prevent desynchronisation due to imperfections in the 555 timers and multivibrator circuits.MOSFETs M1 And M2 alternate at the output signal from the multivibrator at around 10MHz. C1 is acting as a tank to store energy, but only when M1 is active. When M1 turns off and M2 activates, the energy stored in C1 gets discharged to the primary of the fly back transformer. Using this capacitive storage supplies higher current and energy, and prevents directly shorting the high power supply through the low-resistance primary windings of the flyback transformer, as the low resistance essentially provides a short circuit path and potentially could damage the supply.The DC pulse is sent through the fly back transformer, where it is converted to high voltage (~3.5 KV). It charges C2 until the energy stored is strong enough to jump across the spark gap and send the high power - high voltage charge through the primary of the Tesla Coil. The pulse is converted to an even higher voltage in the Tesla Coil’s secondary.Pros:-556 timer is not very power-hungry-Using capacitive energy storage prevents directly connecting low resistance load to supply, and also allows higher energy to be delivered-Astable multivibrator is simple, easy to build-High frequency allows more continuous stream of sparks-Spark gap, C1, charge resistor in AMV circuit, and C2 can be adjusted to allow precision tuning and resonant frequency tuning-Use of MOSFETs allow much higher voltage being delivered to the fly back transformer-Use of spark gap ensures high energy pulse is delivered to the primary of the Tesla Coil.Cons:-Use of two power supplies is tricky and more space consumption is created(though this could be remedied using a power supply module)-MOSFETs could fry if back EMF is high enough (though the flywheeling diode should stop this)-Grounds can be connected for the operation of MOSFETs, but lack of isolation could put the multivibrator at risk of interference or even exposure to back EMF (worst case scenario)-While C1 could be polarised, the rapid discharge of it through the low-resistance primary of the flyback could significantly shorten it’s life. Using a ceramic capacitor would work as well and charge up far faster than an electrolytic, but less energy is stored and therefore less energy is pushed through the fly back primaryAll feedback is welcome. Thanks!

author: dmills
author_rank: Super Contributor
timestamp: January 09, 2020, 06:00:47 pm
content: Actually efficiency will suck if it works at all, go back to the drawing board.Consider C1 is discharged, you turn on M1, what limits the charging current in C1 (Hint, if it is anything except an inductor or a current source power supply, fully half your input power will wind up as heat in the current limiter or mosfet, that's just basic physics).Also your gate drive arrangements need a connection to each of the source terminals on the mosfets....Your flyback is rater screwed up by the presence of the catch diode in any case, for a step up flyback you want to let the primary ring up until the energy transfer to the secondary limits the voltage (A snubber deals with the leakage inductance).The NICE thing about flyback switched mode converters is that they are INHERENTLY energy limited by the fact that the energy stored in the field is 1/2LI^2, you can control the power thruput by simply varying the frequency (on time should be controlled to limit core saturation).

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: January 09, 2020, 06:30:56 pm
content: Quote from: dmills on January 09, 2020, 06:00:47 pmWhat kind of driver do you recommend? I have limited components, and I prefer SGTC due to high energy delivery capabilities. I want to be able to use a high frequency as well so that the stream of sparks is more steady. The fly back transformer is to convert low voltage DC pulses into higher voltage pulses, to charge the capacitor in the spark gap arrangement.Could I use a current limiting resistor in series with the capacitor? Or an inductor? Resistors limit current efficiently in terms of functionality but waste energy in the form of heat in terms of actual efficiency.Tesla Coils are an art, a very precise one.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 10, 2020, 09:35:43 pm
content: I used a Royer oscillator (IRFP260n x2) to drive a surplus TV flyback transformer, which output was then used to charge a cap bank/multi-electrode fixed gap/TC primary. The whole shebang is powered by 2 little 12V 5Ah SLAs. For a few minutes..... lol....

author: Jwillis
author_rank: Super Contributor
timestamp: January 11, 2020, 11:47:50 pm
content: Quote from: WyverntekGameRepairs on January 09, 2020, 06:30:56 pmIntroducing the resistor increases the decay of the LC oscillator , which is also known as damping. The resistor also reduces the peak resonant frequency. During each spark across the gap there is more than just one oscillation. When the capacitor reaches a threshold and discharges because the air between the Gap reaches a breakdown . This charges the inductor . when the cap reaches the fully discharged state the inductor discharges back into the capacitor. This happens over and over until the Gap quenches. The resistor slows the transfer of current between the cap and inductor there by slowing the oscillation and changing the resonant frequency of oscillation.This of course requires very high voltages so the air between the gap can break down. You can use Switching Spark Gaps (SSG) to make it more efficient and lower the breakdown voltage.Because of the need for high voltages , a HV flyback transformer is used to power the LC circuit.In order for you to drive the high voltage fly-back with a low voltage DC supply you need to change that DC supply to either an alternating current or pulsing DC current so the magnetic feild of the fly back transformer can charge then relax on each cycle from the primary . This allows the secondary current to flow one way then the other.By using a oscillator you drive the primary of the flyback . You can use an Astable 555 Oscillator Circuit to drive either BJTs or mosfets to drive the fly back transformer. Try not to use CMOS or LinCMOS 555 timers without shielding them. The high voltage from the tesla coil can destroy them much easier than BiPolar 555 timers , if they are to close to the coil.Just to add. Tesla coils resonate . So the diameter ,length and number of winding's determine at what frequency the coil will resonate most effectively. So they need to be tuned by changing the oscillation of the primary LC circuit. This is done by changing the value of the primary inductor coil by being able to move the input to anywhere on the primary .

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 12, 2020, 08:51:44 pm
content: Indeed, Tesla coils resonate. In fact, they do so _by definition_. A "Tesla Coil" is an air-core quarter-wave helical resonator of high Q. How you get the thing to resonate, ie ring like a bell, is done in various ways, most of which result in pulsing a primary coil wrapped around the helical resonator proper, at the proper location of course. Fast rise and fall times of the pulses to the primary are necessary, hence you find rotary spark gaps, magnetically quenched gaps, blown gaps, multiple element gaps -- all with the idea of high power throughput without sacrificing rise/fall times by forming a persistent power arc instead of a rapidly forming and decaying spark.There are many online aids for calculating parameters of the helical resonator and its primary. Such as:http://www.classictesla.com/java/javatc/javatc.html