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Registered Member #3595
Joined: Mon Jan 10 2011, 04:46AM
Location:
Posts: 26
James wrote ...
JKowalski wrote ...
Trying to make a high def multi-kilowatt tesla coil is like trying to play mozart with cannons - not really the right tool!
I'd love to see someone try playing Mozart with cannons though :)
I guess we have to settle for Tchaikovsky's 1812 Overture...
But to stray back on topic, tesla coils are all about the challenge to me. As far as hobby electronics go, they are probably the most visually impressive and satisfying project to build. Sometimes when you work with electronics for a while you get an urge to create something just plain COOL. I really can't think of any practical use for them save the previously mentioned equipment testing. Well, maybe an ozone generator O_O
However, since you seem to define "uses" as being also "what I can also drive with the same circuit" from reading your first post... H-bridges are very multi-purpose devices. Especially considering the hardiness of the bridge required for Tesla coil use... I'm sure many people here could answer the question "what could I do with a high-frequency high-power H-bridge?"
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
JKowalski wrote ...
magnet18 wrote ...
I know they can be audio-modulated, why is it that the large ones never have good sound quality?
It is difficult to control that much power precisely... High power devices like some of the larger coils need to be operating within strict conditions to avoid disastrous failures...
Most of the larger coils (almost all DRSSTCs) require an interrupter circuit to work (it prevents the resonant primary circuit from ringing up to unmanageable power levels). This interrupter circuit usually operates within the audible range, so attempting to play high def audio over this is basically pointless as the interrupter-modulating arcing drowns out everything. The way most DRSSTCs are audio modulated is to make the interrupter BE the audio frequency, but this means the audio quality is terrible (coil is only capable of playing square wave monopohonic sound)
Plus the high power arcs create a ton of noise on their own that tends to drown out most things!
With smaller coils, the arcs are less fierce and quieter meaning less background noise and modulation schemes like PWM and FM are much easier to implement at those power levels.
If you want really good audio quality your options are limited to low power coils and stable-arc plasma speakers. Trying to make a high def multi-kilowatt tesla coil is like trying to play mozart with cannons - not really the right tool!
so if it could be pulled off, people would $#!^ bricks...
wrote ... it prevents the resonant primary circuit from ringing up to unmanageable power levels
like gigawatts, or like teravolts? and so if you didn't have one it would just resonate itself apart? (in the electrical sense)
Registered Member #3595
Joined: Mon Jan 10 2011, 04:46AM
Location:
Posts: 26
magnet18 wrote ...
wrote ... it prevents the resonant primary circuit from ringing up to unmanageable power levels
like gigawatts, or like teravolts? and so if you didn't have one it would just resonate itself apart? (in the electrical sense)
and what you say makes sense, thanks
To quote our wiki:
A DRSSTC is different than the conventional SSTC due to the addition of a primary tank capacitor, hence, "Dual Resonant." When in a resonant state, the added capacitance in the primary circuit cancels the inductance leaving no reactive component. Primary current flow is now only limited by resistance in the capacitors (ESR) and resistance in the primary windings, which is usually on the order of a few hundred milliohms. In a SSTC, primary current is limited by the primary's inductance and streamer loading. This is the reason a SSTC can run CW or "continuous wave". So a key difference between SSTCs and DRSSTCs is that a DRSSTC usually operates in the transient state, while SSTCs can safely run in the steady state conditions. However, if you were to drive a DRSSTC at it's resonant frequency for too long, a steady state current of many times the safe limit might be possible. This could have the following adverse effects IGBTs blow from overcurrent - this would happen almost instantanly (few mS) depending on the size of the IGBT. Overvoltage of the primary capacitor - The extreme current flowing over the primary tank can create voltages tens of times more than the supply voltage. (use Ohm's law to figure out just how high) Therefore we use an interrupter. An interrupter turns on the drive circuits for a determined amount of time (typically 50-300uS), and then shuts them off (typically 2-20mS). This low duty cycle keeps the IGBTs from overheating severely. Active overcurrent detection (OCD) circuits can arrest high currents that might develop before the interrupter shuts off. A common reason for sudden current draw would be a ground strike, which dramatically changes the impedance of the tank circuit (it increases the Q).
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
JKowalski wrote ...
magnet18 wrote ...
wrote ... it prevents the resonant primary circuit from ringing up to unmanageable power levels
like gigawatts, or like teravolts? and so if you didn't have one it would just resonate itself apart? (in the electrical sense)
and what you say makes sense, thanks
To quote our wiki:
A DRSSTC is different than the conventional SSTC due to the addition of a primary tank capacitor, hence, "Dual Resonant." When in a resonant state, the added capacitance in the primary circuit cancels the inductance leaving no reactive component. Primary current flow is now only limited by resistance in the capacitors (ESR) and resistance in the primary windings, which is usually on the order of a few hundred milliohms. In a SSTC, primary current is limited by the primary's inductance and streamer loading. This is the reason a SSTC can run CW or "continuous wave". So a key difference between SSTCs and DRSSTCs is that a DRSSTC usually operates in the transient state, while SSTCs can safely run in the steady state conditions. However, if you were to drive a DRSSTC at it's resonant frequency for too long, a steady state current of many times the safe limit might be possible. This could have the following adverse effects IGBTs blow from overcurrent - this would happen almost instantanly (few mS) depending on the size of the IGBT. Overvoltage of the primary capacitor - The extreme current flowing over the primary tank can create voltages tens of times more than the supply voltage. (use Ohm's law to figure out just how high) Therefore we use an interrupter. An interrupter turns on the drive circuits for a determined amount of time (typically 50-300uS), and then shuts them off (typically 2-20mS). This low duty cycle keeps the IGBTs from overheating severely. Active overcurrent detection (OCD) circuits can arrest high currents that might develop before the interrupter shuts off. A common reason for sudden current draw would be a ground strike, which dramatically changes the impedance of the tank circuit (it increases the Q).
Ahh, thanks, I still need to do some reading before I build one of these, get the theory down... just gotta make it to may 8th, then my life gets freed again...
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
JKowalski wrote ...
magnet18 wrote ...
I know they can be audio-modulated, why is it that the large ones never have good sound quality?
The way most DRSSTCs are audio modulated is to make the interrupter BE the audio frequency, but this means the audio quality is terrible (coil is only capable of playing square wave monopohonic sound)
I actually had an idea;
With the SG3525 plasma speaker, it uses audio modulation with the square wave it outputs to effectively create music.
I'm thinking that could be used to create the interrupter with much cleaner and better sounding results!
Maybe I'll give a shot at designing a DRSSTC... Don't be too surprised if it blows up
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
The duty cycle of an appreciably sized DRSSTC is severely limited to a few percent at most. You can only achieve so much resolution when you have 5-10 cycles per beat, and only up to about 1000 beats per second. Not to mention, the power output of a drsstc resonant tank does not scale linearly with on time.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
James wrote ...
I don't think anyone has ever come up with a practical use for a Tesla coil. Even Tesla himself never really got anywhere with that.
Not so fast, Boy Wonder!
J. Chem. Educ., 1991, 68 (6), p 526 Efficient, inexpensive, and useful techniques for low vacuum leak detection with a Telsa coil Gary S. Coyne and Cathy L. Cobb
Abstract
Probe gases should be used as a spray in sealed environments when testing for leaks.
J Electron Microsc Tech. 1987 Sep;7(1):29-33. A glow discharge unit to render electron microscope grids and other surfaces hydrophilic. Aebi U, Pollard TD.
Abstract
We describe the design, construction, and operation of a simple glow discharge unit that can be used to make surfaces such as carbon-coated electron microscopy grids and glass coverslips hydrophilic. The use of a vacuum leak detector (Tesla coil) in place of a conventional high-voltage power supply and a small plastic desiccator for the vacuum chamber make the unit very inexpensive. Owing to the small volume of the chamber and the simplicity of the unit, the whole glow discharge process can be carried out in only 2 to 3 min, a time considerably shorter than that required for conventional vacuum evaporators. The hydrophilic surface improves adsorption of particles by several orders of magnitude in preparation for negative staining, freeze-drying, and other procedures.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
The literature is actually full of examples where "Tesla coils" are being used for scientific and industrial applications.
(I use the quotation marks because sometimes the devices being used may not look like a classical "Tesla coil", or be described as such, but they are essentially the same thing).
Here's an example where one is being used to accelerate electrons for an industrial application:
(Note that this device is apparently a prototype for a larger unit which will operate at a megavolt, and at a power level of up to a MW).
Being that I'm interested in such things, I was curious as to how this device actually works, so I simulated it. (I know, I should get a life).
Anyway, they don't go into a lot of detail on the design and construction, but, going on the things they mentioned (e.g., the resonant frequency, L and C per meter, the external dimensions, and the pictorial representation), and some guessing, I did an EM simulation and came up with a coupling coefficient of about 0.38.
Then I plugged the values I came up with into "Circuitmaker2000", a spice simulator, and arrived at this circuit representation:
Although in the paper they mentioned that they are driving the accelerator with "500 volt pulses", I just used a MOSFET half-bridge operating with a 500 volt supply for the simulation. And here is the simulated output voltage and power into a resistive load:
So there is a real world example of a "Tesla coil" being used for something practical.
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
JKowalski wrote ... However, since you seem to define "uses" as being also "what I can also drive with the same circuit" from reading your first post... H-bridges are very multi-purpose devices. Especially considering the hardiness of the bridge required for Tesla coil use... I'm sure many people here could answer the question "what could I do with a high-frequency high-power H-bridge?"
Induction heater also comes to mind
So if I wanted I could build a circuit to power both an induction heater and a tesla coil, just plug and play?
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Uses for a Tesla Coil?
