Author Topic: 230 volts spark gap  (Read 2995 times)

Offline Quentief

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230 volts spark gap
« on: February 03, 2020, 06:57:51 PM »
Hi everyone,

I would like to know if it is possible to design an arc oscillator (the spark gap circuit, or the primary circuit on a Tesla Coil) which would be able to use a voltage as low as 230 volts, instead of something about some kilovolts. According to my own experience, we cannot make electric arcs from 230 volts, the voltage is too low to make stable and sustainable electric arcs.

But I would like to have your mind-view on this question.

And I apologize in advance if my English is not perfect, actually I am French :) But I will try to do my best to be understandable.

Offline klugesmith

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Re: 230 volts spark gap
« Reply #1 on: February 03, 2020, 07:06:50 PM »
How about using a "gas discharge tube" surge arrestor?
Those are enclosed spark gaps with relatively low, well specified breakdown voltages.  Easy to get from electronic component distributors or ebay, etc.

https://www.bourns.com/products/circuit-protection/gas-discharge-tube-(gdt)-surge-arrestors/2-electrode-gdts


They might not be a good fit for Tesla coil circuits where you want a spark on every cycle of AC power.
Maybe worth a try.  You could make a mechanical or solid state interrupter to make TC primary circuit fire less frequently.  Once fired the GDT will have a very low impedance in both directions, just like a spark.

Another idea is a regular spark gap in partial vacuum.
A look at Paschen's Law suggests that that can't get you down to 230 volts, no matter how close the electrodes are set, at any pressure.  The peak voltage at 230 volts RMS might be reachable.  In argon?


« Last Edit: February 03, 2020, 07:21:52 PM by klugesmith »

Offline Quentief

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Re: 230 volts spark gap
« Reply #2 on: February 03, 2020, 07:21:03 PM »
Thanks for your reply 🙂 I didn't know these components. Is their voltage breakdown enough little to be used in 230 volts ?

Offline Quentief

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Re: 230 volts spark gap
« Reply #3 on: February 03, 2020, 08:16:29 PM »
Your solution is really interesting me. But I think I will keep it for another time. I do not have such components and I need to make some researches on them before to use them.

Furthermore, I have seen people on YouTube which were able to draw electric arc from 230 volts.

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Apparently they were using coils or capacitors. Can I use this in a Tesla spark gap ? And how can I design capacitors or coils for this function ? I mean, I know the phenomenon (I=C*dU/dt and U=L*dI*dt) but how can I find the capacity or the inductance required for this purpose ?

Offline MRMILSTAR

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Re: 230 volts spark gap
« Reply #4 on: February 03, 2020, 08:55:11 PM »
Once you establish a plasma channel, which has almost no resistance, even very low voltages can sustain an arc. You can draw an arc from 240 volts if the current is sufficient but it can't initiate an arc. Just touch the electrodes and draw them apart assuming the circuit breaker doesn't trip. You would need a ballast to prevent that. You can even do it with very low voltages, an arc welder for example. They operate at about 20 volts but have very high current. But that is quite different than firing a spark gap without the electrodes touching. For that you need about 3000 v/mm of gap spacing.

Even if you could bridge a spark gap with such low voltage, you probably would not want to build such a SGTC. This is because the energy in the capacitor is related in a non-linear fashion to the voltage but only in a linear manner to the capacitance as can seen in the capacitor energy equation as:

E = 0.5*C*V*V

where E is joules, C is farads, and V is voltage. You would need a very large capacitance from a pulse-rated capacitor to obtain a decent amount of energy per bang from such a low voltage. Its easier to get energy from voltage than capacitance.
« Last Edit: February 03, 2020, 09:10:03 PM by MRMILSTAR »
Steve White
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Retired electrical engineer

Offline Quentief

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Re: 230 volts spark gap
« Reply #5 on: February 03, 2020, 10:05:19 PM »
Well I have already tried to draw electric arcs from 230 volts. I built a very simple circuit : two electrodes were connected in series with an electric kettle (its resistance was limitating the current). However, the system was only able to work with carbon electrodes. When I was trying to draw electric arcs with iron electrodes (screws,nails,...), I was not able to get anything. Next, I added a diodes bridge to have a rectify signal but the result was the same. I have never found an explanation to this problem. But like I said, I have been told that my system needs something to filter the current or maybe the voltage from the diode bridge. But I do not know how to do that.

I know there is maybe nothing to do with my previous question but if you know how to calculate the capacity or the inductance required to stabilize the electric arc, I am more than interested.

Offline davekni

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Re: 230 volts spark gap
« Reply #6 on: February 04, 2020, 04:54:31 AM »
50/60Hz is slow enough that the arc tends to go out at the voltage zero-crossings, even if full-wave rectified.  The ionized air recombines (becomes unionized) too fast.  Higher voltages can restart the arc with the small amounts of remaining ions.

I haven't personally played with 230V arcs, but inductor filtering is likely best.  A capacitor filter would require current limiting after the capacitor to keep the arc from discharging the capacitor too far.  For inductance calculation, a SPICE simulation would be ideal.  For rough estimation, the AC component of rectified 50Hz line is 100Hz.  Find an inductor with at least the same impedance as your electric kettle (series current-limiting impedance) at 100Hz.  Higher is even better.

As Steve pointed out, 230V for a Tesla primary has many issues.  Another is that your primary coil would need to be ~0.2 turns :)

If you really want to experiment with SGTC circuits "directly" from 230V line (no line-frequency transformer), a diode/capacitor voltage multiplier could get the voltage high enough for a single-turn primary.   Perhaps two voltage-doublers, one + and one - , to get +- ~600V peak.  The first cap in each doubler could be a larger electrolytic.  The second could be each side of a 2S MMC.  This would provide only 50 sparks/second, requiring a full cycle to charge both halves of the MMC.  For the spark gap, either a rotary synchronous design with electrodes that touch slightly, or a triggered spark gap (short gap with small trigger electrode connected to a small HV pulse circuit).  Even at 1200V total, your primary will be one turn, so stray inductance in the spark-gap and wiring will make the coupling factor rather low.  (My SGTC is fairly low voltage, 9kV into a 3-turn primary.  Even there, stray inductance reduction is important.)

If you want a 230V spark gap for some other use, triggered gaps can run that low, at least for argon.  Higher-end TIG welders use a high-voltage trigger pulse to start the arc, avoiding the need to touch the electrode to the work piece, and thus keeping the electrode cleaner.  The same thing should work for a separate trigger electrode.  (Of course, this is for high arc currents.  May not work at lower current.  May not work as well in air either.)
David Knierim

Offline Quentief

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Re: 230 volts spark gap
« Reply #7 on: February 06, 2020, 02:49:43 PM »
Thank for all of your answers. I built an inductance, I used an iron core from an old transformer, I wound about 30, maybe 35 turns of coil. According to my calculation, I think I have an inductance between 100 and 140 mH. I connected it in serie with the DC output from the diode bridge and you were right : the coil seems to help electric to be formed.

It is not as powerful as what I was expecting. I don't have the instruments to measure the current and the voltage, to calculate the power of the electric arc, but I was expecting something able to melt the iron from the electrodes. But again, thanks it was really interesting to experiment it.

Now concerning my first question, well actually I do not want to build a Tesla coil, I just want to increase the frequency of the main 230 volts 50Hz. Indeed, I am not looking for very high voltages. I found the primary circuit of the Tesla coil very interesting and I would like to know if it is possible to apply its working principle to a lower voltage.

So, according to you, a classical spark gap cannot operate with 230 volt because of the air breakdown voltage. I suppose the rotary spark gap solution could work : if the contacts are touching them together at each cycle, the voltage does not need to be very high.

The solution proposed by klugesmith is also interesting : a spark gap in a different gas. Can I use a Fluorescent lamp as a spark gap ? If I have understood their functioning properly, the gas inside the lamp is designed to let the current passes threw with a lower voltage than if it was in air.

Offline ElectroXa

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Re: 230 volts spark gap
« Reply #8 on: February 06, 2020, 06:31:54 PM »
For fluorescent lamp spark gap, it's a bad idea because
1) they trigger at around 500V, so 325V DC won't pass through the lamp unless if it was triggered with a high voltage pulse ;
2)the DC voltage will tear one electrode faster than the other, leading to failure,
3) and finally,  fluo lamp won't withstand such a high (pulse) current.


Offline davekni

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Re: 230 volts spark gap
« Reply #9 on: February 07, 2020, 05:47:25 AM »
If your 30-35 turn inductor is wound on a standard un-gapped transformer core, it may be saturating, causing inductance to drop at higher current parts of the waveform.

What is the resistance (or power rating) of your electric kettle ballast?

Arc welding is typically done at 50+ amps and <20V.  A 1000 watt kettle would limit to ~4.4A, much less than an arc welder.  Voltage across the arc is still dropping to ~20V, so arc power may be too low to melt the electrodes.  Even so, at 4.4A, I'd recommend some eye protection for the relatively-intense UV.

As already mentioned, a fluorescent tube won't work for multiple reasons.  A low-pressure argon gap might work.  A spark gap triggered by a small HV trigger pulse is more likely to work.

Depending on what you are trying to accomplish, electronic switching is probably much better than any spark-gap or mechanical (rotary) switching.  Are you after short high-power bursts of higher frequency?  Would longer bursts of lower peak power (same energy) work?  If you share more about your goals, it would be easier to suggest solutions.
David Knierim

Offline Quentief

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Re: 230 volts spark gap
« Reply #10 on: February 07, 2020, 11:04:18 AM »
Could you explain me how I can calculate the maximum current that my inductance can tolerate before to be saturated ?

Concerning the electric kettle, it has a 22 Ohms resistance, so the current is limited at 10 amps, but it still stay very lower than the current from arc welders.
However, some argues that it is possible to weld by using the main voltage, is it a fake ?

https://www.instructables.com/id/Water-and-salt-Welder/

Concerning what I am looking for, actually I would like to try to induce current in metal, to heat them. In that respect, I would like to know if the primary circuit from Tesla coil can be adapted for that purpose.

Offline Twospoons

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Re: 230 volts spark gap
« Reply #11 on: February 07, 2020, 11:00:54 PM »
GDTs come in trigger voltages as low as 90V.  A little reading reveals the low voltage is achieved by adding a little Tritium to the gas fill. I'm guessing the Beta emission provides some pre-ionisation of the gas fill to lower the trigger voltage.

So theres your clue - you can build a 230V spark gap, but you'd want some form of pre-ionisation to lower the trigger voltage.
Electrode shape will also be important - you want sharp points to increase the field gradient.

Offline davekni

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Re: 230 volts spark gap
« Reply #12 on: February 08, 2020, 05:04:13 AM »
Spark-gap drive for induction heating!  I've not seen that before.  It could possibly work, but has many down-sides.  Most induction heating uses continuous drive (or with amplitude following the incoming rectified line-voltage profile, as in induction cook-tops).  With pulsed drive, the resonant capacitors need to handle much higher peak voltage and peak current.  The work coil also needs to handle high peak current, which could become an issue at higher powers due to pulsed magnetic forces on the coil and object being heated.  And, as you've seen, a high-current low-voltage spark gap is difficult too.

There are many induction heating threads on this forum.  If your goal is useful induction heating, I'd suggest reading those.  If you are more interested in the fascinating challenge of trying something unique, have fun with spark gap induction-heater drive!

Concerning saturation current of your inductor, you can measure that with a scope and capacitor.  Charge the capacitor, then connect it across the inductor, measuring the voltage waveform across the inductor.  The capacitor's initial energy needs to be high enough to saturate the inductor, which will show up as flat-topped half-cycles in the ring-down waveform.  Once the amplitude rings down enough to not saturate, the waveform will be a better sine-wave approximation.  Pick a half-cycle that is still slightly flat-topped, then zoom in on the zero-crossing at the end of that half-cycle.  The voltage slope times capacitance gives the current.

Welding with line voltage:  Most breakers can handle short-term overload.  The 120V circuit in the instructable was probably being ran at ~30A for welding.  There are comments from people being unsuccessful with 230V circuits (probably lower current available) and of breakers tripping.

For a low-voltage spark-gap, yes, an ionization source helps.  Radioactive isotopes are hard to come by and generally dangerous.  Hard UV light is another option, but also hazardous.  Given the high currents needed for your low-voltage spark gap, it will need aggressive cooling.  That makes contained gasses difficult.  The spark (arc really) needs to be extinguished quickly after each discharge, implying either electrode motion (rotary gap) or high gas velocity through the gap.  My off-hand guess is that a rotary "gap" with tungsten electrodes may be the only reasonable option.  Electrodes will need to touch to start the arc, and likely air flow directed at the gap to avoid too much molten metal.

At the high currents you need, any sharp point will melt/sputter away quickly.  That's why I'm thinking a rotary gap with contact is the only option.

I'd also suggest a resonant charging circuit (inductor in the 230V supply tuned to one half-cycle per spark event when coupled with the resonant capacitors).  There's more about resonant charging for SSTCs on the forum.

Good luck!
David Knierim

Offline Quentief

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Re: 230 volts spark gap
« Reply #13 on: February 09, 2020, 01:12:41 AM »
Thanks for your answers, I now understand better. You are probable right about the induction heater, I think I will have a look at the induction heating threads before to go further on this subject. Thanks for your help.

I would like to ask you some questions about the inductance that I was trying to make : I think I did not calculate its inductance propely. Like I previously said, I use an iron core from an old transformer to make this inductance. A photo should be available in attachement.

To calculate its inductance, I use this formula :
L=μ0*μr*N²*S/l= 69 mH
with:
μ0 = 4π × 10−7 T m/A
μr = 2000
N = 35 turns
S = 9 cm²
l = 4 cm

Actually, I used the same formula for a solenoid. The parameters S and l are the dimensions of the core's part which is encircled by the coil. I do not know if I am wrong or not by considering the problem in this way. Furthermore, the core does not have a space to limit its saturation. I am sorry, I cannot find the English translation for that, in French we call that "l'entrefer" https://tse2.mm.bing.net/th?id=OIP.srfRsINmFNKAi-aLxlUFLAAAAA&pid=Api&P=0&w=300&h=300 , so maybe you are right, the saturation makes my inductance unable to have the desired impedance for the creation of 230 volts electric arcs. (the current used is about 10 Amps)
« Last Edit: February 09, 2020, 01:16:18 AM by Quentief »

Offline johnf

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Re: 230 volts spark gap
« Reply #14 on: February 09, 2020, 03:52:08 AM »
I think you are confusing 50/60 Hz AC with DC
All your linked videos had either stepup transformers AKA neon transformer in one vid or high frequency home made transformewr pair in another vid, or used DC with an inductor to raise the voltage substantially above mains voltage. Yes all were powered from mains but not direct connect to mains

Go find a nice big OLD neon transformer without the GFC

Offline klugesmith

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Re: 230 volts spark gap
« Reply #15 on: February 09, 2020, 05:33:29 AM »
Nice work, making that choke from old transformer core.
The formula you used seems appropriate, except the term for length is for a complete magnetic flux loop (through center bar, end bars, outside bars, then returning to center bar.  length of 9-square-cm steel path that completely encircles the coil. 

WHen you understand why the formula works, then it's easy to determine the saturation current, and to see what happens when you add an air gap (reduced inductance and increased saturation current).  There are many excellent introductions to transformer design.
 

Offline davekni

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Re: 230 volts spark gap
« Reply #16 on: February 09, 2020, 06:23:41 AM »
With the I-pieces separate as you show, it's easy to add a gap.  You may already have somewhat of a gap due to laminations not exactly lining up at the joint between E and I pieces.

Adding a small gap also makes inductance vs. current much flatter.  The permeability of silicon-iron (transformer steel) varies significantly as flux density increases.  The gap is linear (air), making the resulting inductor more linear.

To calculate saturation current, you'll need the saturation field of silicon-steel, around 1.6 to 1.7T if I recall correctly.
David Knierim

Offline Quentief

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Re: 230 volts spark gap
« Reply #17 on: February 10, 2020, 01:19:11 AM »
Maybe my idea to reuse the transformer core to make my choke was not a sensible idea. I mean, despite the good magnetic permeability, the EI form makes the magnetic circuit length too long + the saturation phenomenon -> maybe I should use something else

Offline klugesmith

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Re: 230 volts spark gap
« Reply #18 on: February 10, 2020, 02:38:00 AM »
The magnetic path length in steel core is driven by need to go around the winding window.
Just as the wire length per turn is driven by need to go around the center leg of core.

There's not much room for improvement, over conventional E-I core shape.  The magnetic path length in a toroid still needs to reach around the winding window area, and the wire length per turn still needs to reach around the cross-sectional area of the core. 
If your coil of wire doesn't fill up the winding window, performance can be improved by using thicker wire, or find a smaller core.

When you make a choke with intentional air gap, the maximum stored energy (0.5 * L * I^2, at saturation) is proportional to air gap volume, and to the square of B_max. Steel beats ferrite by a large margin in that last factor.
« Last Edit: February 10, 2020, 02:51:13 AM by klugesmith »

Offline davekni

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Re: 230 volts spark gap
« Reply #19 on: February 10, 2020, 04:56:27 AM »
I agree that E/I silicon-iron (transformer steel) laminations are about as good as it gets for line-frequency inductors.  (Cobalt alloys are better, but quite expensive.)  Klugesmith, did you mean "find a larger core"?  For more stored energy and/or better efficiency (less winding power loss), a larger core is better.

If you can get a couple microwave oven transformers and access to a steel-capable band-saw or large chop-saw, two primary halves wired in parallel and physically stacked with a small gap works well for line-frequency inductance.
David Knierim

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Re: 230 volts spark gap
« Reply #19 on: February 10, 2020, 04:56:27 AM »

 


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[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
futurist
September 27, 2020, 07:49:49 PM
post Stroboscopic photography & motors
[Digital Compact Camera]
klugesmith
September 27, 2020, 07:08:06 PM
post Re: Led Closeups with Mobile phone and lens .
[Smart Phones]
klugesmith
September 27, 2020, 06:43:46 PM
post Re: DRSSTC Tuning for Music vs Big Sparks?
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
September 27, 2020, 06:42:46 PM
post Re: Finding accelerometer location inside a phone
[Smart Phones]
klugesmith
September 27, 2020, 06:36:41 PM

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