Author Topic: First test of the SSTC  (Read 4043 times)

Offline davekni

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Re: First test of the SSTC
« Reply #20 on: January 21, 2023, 05:44:15 AM »
Quote
Dave, as for the fets, they could be fake. I got them from a marketplace in my country. Below is the photo of the fet taken apart, I was curious about how it looks like on the inside :D
Since the die area looks similar to genuine parts, it could be just a newer version from Vishay.  Or it could be a better-quality counterfeit part.

Quote
From the JavaTC I can see it is around 27k. Is that bad ? If it is, is there a way to fix it or I need to construct a new secondary ? Also, why is 50k a good thing, shouldn't lower values be better ?
50k secondary impedance is something I learned from this forum.  Built my first three coils before finding this.  My SSTC happens to be 50k.  My larger DRSSTC is 34k.  It has a high peak power H-Bridge suitable for lower impedance impulsive arcs.  50k is not a critical magic number.  Here are a number of forum links including some explanations:
https://highvoltageforum.net/index.php?topic=115.msg722#msg722
https://highvoltageforum.net/index.php?topic=937.msg6293#msg6293
https://highvoltageforum.net/index.php?topic=1066.msg7682#msg7682
https://highvoltageforum.net/index.php?topic=2284.msg16721#msg16721
https://highvoltageforum.net/index.php?topic=1538.msg12055#msg12055
https://highvoltageforum.net/index.php?topic=1872.msg14039#msg14039
In general, it seems that >50k is better for smaller or lower-power coils and <50k is good for large high-power coils.  You may have trouble getting enough power into your 27k secondary for voltage to get high enough to create good arcs.  Perhaps you could try newer higher-power FETs.
A smaller top load will raise frequency and impedance, but also has disadvantages.  Winding a new secondary may be the best option.

Quote
Thanks a lot for the help and explanations Dave, this means a lot to me. I love learning new things and this forum is an awesome place to do so :)
I too have learned a lot from this forum in the 3.5 years since I found it.  Would have saved me some time and work in building my coils if I'd found it earlier.  Could have avoided reinventing things that were already known.
David Knierim

Offline LoOdaK

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Re: First test of the SSTC
« Reply #21 on: January 21, 2023, 03:01:21 PM »
Quote
In general, it seems that >50k is better for smaller or lower-power coils and <50k is good for large high-power coils.  You may have trouble getting enough power into your 27k secondary for voltage to get high enough to create good arcs.  Perhaps you could try newer higher-power FETs.
A smaller top load will raise frequency and impedance, but also has disadvantages.  Winding a new secondary may be the best option.

How could that improve my power transfer to the secondary ? Do you mean I could push more current through the primary ?

I'm quite uncertain what I should do regarding the number of turns of the primary. Should I increase them or decrease them? I read in one of the links above that I should also watch my primary impedance. If I got it right, lowering primary impedance is going to allow more current through the primary but will of course stress transistors more. I calculated my primary impedance to be around 14.4 ohms with the current setup.

Lowering the diameter of the primary coil to 8cm while keeping my number of turns the same gives me a coupling coefficient of 0.4+. It's a bit too much maybe but thing which concerns me the most is the secondary reactance. With the new primary, reactance drops to around 20k. Primary impedance also drops to around 9 ohms. So it means that I don't actually gain any performance benefits from this, or very little. If my hypothesis is right, this would allow more primary current but if my secondary reactance drops to 20k, the secondary "won't be accepting" that power actually and I even risk getting sparks from the secondary to the primary.

I'm pretty confused as to what I should do.

I could also get some K60H603 IGBTs, would they work ? They seem to be higher-power than IRFP460.


More precise measurements, new JavaTC values:



After modifying primary:





EDIT: After playing a little bit I think I could try this design:



I kept the diameter of the primary coil to ~11 cm, and increased spacing between turns, so the primary height should be around 94mm with the same number of turns (7). That should increase coupling to around 0.379. The decrease in secondary reactance is minimal, but the impedance of the primary is quite lower, resulting in around 7.1 ohms. If I take an approximation, that should result in ~23A of current through the primary according to Ohm's law (probably not accurate because I don't know the better formula, but good enough I think). I think that IGBT could drive this (maybe even IRFP460 ? )

This could work a little bit better I think.
« Last Edit: January 21, 2023, 04:31:40 PM by LoOdaK »

Offline davekni

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Re: First test of the SSTC
« Reply #22 on: January 21, 2023, 08:19:31 PM »
Quote
How could that improve my power transfer to the secondary ? Do you mean I could push more current through the primary ?
Yes, more current without FETs failing.  Lower primary impedance will increase current.  Higher coupling will transfer more power to secondary.  Primary current phase will shift closer to voltage phase.  Real power will be higher for any given current.

Quote
I could also get some K60H603 IGBTs, would they work ? They seem to be higher-power than IRFP460.
IGBTs require 15Vge rather than 10Vgs of FETs.  IGBTs also generally have higher switching losses in hard-switched applications like most SSTCs.  (It is possible for an SSTC with high coupling to switch at zero current, but that is rare.)  Some SSTCs do use IGBTs.  Usually lower-frequency designs.

Quote
EDIT: After playing a little bit I think I could try this design:
Yes, something like this is much better.  SSTC primary should generally be at bottom of secondary.  Some insulation between primary and secondary is needed too.  If you can find any plastic pipe or tube a bit smaller than your existing primary form, but still large enough to go over secondary, that would be ideal.  Would get coupling up a bit farther, which improves output power for a given primary current.

Quote
The decrease in secondary reactance is minimal, but the impedance of the primary is quite lower, resulting in around 7.1 ohms. If I take an approximation, that should result in ~23A of current through the primary according to Ohm's law (probably not accurate because I don't know the better formula, but good enough I think). I think that IGBT could drive this (maybe even IRFP460 ? )
23A is close for primary current (ignoring effect of secondary).  Primary voltage is a square wave of +-163V, resulting in a triangle-wave for current.  RMS current is a bit lower, by a factor of PI / (2 * sqrt(3)) or 20.8A.  Peak current is higher by PI / 2, so 36A.  IRFP460 may handle this for short duty cycles.  36A is well within peak current capability, but switching at 36A adds more power dissipation to FETs, and even more so to IGBTs.  Probably worth a try at short duty cycles.  Or add one more turn initially.  One more turn and a little smaller diameter might be ideal.

Good luck with your refinements!

Edit2:  Had to change above sqrt(eight) to 2*sqrt(2) because sqrt(eight) using the digit 8 becomes an emoji.  Then realized my RMS calculation was incorrect, so changed above again.
« Last Edit: January 21, 2023, 09:24:06 PM by davekni »
David Knierim

Offline LoOdaK

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Re: First test of the SSTC
« Reply #23 on: January 21, 2023, 11:47:55 PM »
Quote
IGBTs require 15Vge rather than 10Vgs of FETs.  IGBTs also generally have higher switching losses in hard-switched applications like most SSTCs.  (It is possible for an SSTC with high coupling to switch at zero current, but that is rare.)  Some SSTCs do use IGBTs.  Usually lower-frequency designs.
My GDT output should be around 18V. So would it be a good idea to try it at least ?

Quote
Yes, something like this is much better.  SSTC primary should generally be at bottom of secondary.  Some insulation between primary and secondary is needed too.  If you can find any plastic pipe or tube a bit smaller than your existing primary form, but still large enough to go over secondary, that would be ideal.  Would get coupling up a bit farther, which improves output power for a given primary current.
I will try to make coupling ~0.4. As for the plastic for insulation, I don't think I would be able to find a tube but I will try to come up with something.

Quote
23A is close for primary current (ignoring effect of secondary).  Primary voltage is a square wave of +-163V, resulting in a triangle-wave for current.  RMS current is a bit lower, by a factor of PI / (2 * sqrt(3)) or 20.8A.  Peak current is higher by PI / 2, so 36A.  IRFP460 may handle this for short duty cycles.  36A is well within peak current capability, but switching at 36A adds more power dissipation to FETs, and even more so to IGBTs.  Probably worth a try at short duty cycles.  Or add one more turn initially.  One more turn and a little smaller diameter might be ideal.

Thanks for the explanations. I think I will add one more turn to the primary but I don't think I would be able to make my diameter smaller I will need to stick with 110mm for now and going to make my primary a little bit higher to compensate, I hope that won't cause any problems.


EDIT: Something like this:


If I did my calculations right, around ~27.5-28A peak current, which is lower than before. Although secondary reactance is a little bit lower I think it should work better.


Thanks a lot, I will play with the values a little bit to see what would be the best and easiest way. Will update this thread with new results :)

« Last Edit: January 22, 2023, 12:08:15 AM by LoOdaK »

Offline davekni

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Re: First test of the SSTC
« Reply #24 on: January 22, 2023, 06:21:40 AM »
Quote
My GDT output should be around 18V. So would it be a good idea to try it at least ?
18V should be good for IGBTs.  Do you have gate resistors shunted by diodes?  Needed for IGBTs to get sufficient dead-time, as IGBT turn-off times are longer than turn-on times.

Quote
If I did my calculations right, around ~27.5-28A peak current, which is lower than before. Although secondary reactance is a little bit lower I think it should work better.
Yes, this looks like a good design.  I'm calculating 30.8A peak ignoring secondary.  The direct way to calculate square wave current into an inductor:  During positive half-cycle, inductor current ramps from -peak to +peak.  Current ramps from 0 to +peak in 1/4 cycle.  For 275.45kHz, 1/4 cycle is (1/4)/275.45kHz = 0.9076us.  Integrating the inductor equation of V=L*dI/dt gives I =  V*t/L.  V is 325V/2 for half-bridge.  L is 4.783uH per your latest JavaTC.  So, I = 325V/2 * 0.9076us / 4.783uH = 30.8A.  Of course, this ignores diode and FET/IGBT forward drops, switching times, etc.  Thus reality will be slightly lower peak current.
David Knierim

Offline LoOdaK

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Re: First test of the SSTC
« Reply #25 on: January 22, 2023, 12:53:01 PM »
18V should be good for IGBTs.  Do you have gate resistors shunted by diodes?  Needed for IGBTs to get sufficient dead-time, as IGBT turn-off times are longer than turn-on times.

Yes, I do have 10R on the gate shunted with 1N5819 diode.
Also about gate resistance, do you know any useful links where I could learn some simple methods on how to actually calculate gate resistors, at least approximation for tesla coil bridges ? I watched a few videos and browsed the Internet but it is kind of complicated to grasp for me and didn't quite find a simple way.

Offline davekni

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Re: First test of the SSTC
« Reply #26 on: January 22, 2023, 07:17:25 PM »
Quote
Also about gate resistance, do you know any useful links where I could learn some simple methods on how to actually calculate gate resistors, at least approximation for tesla coil bridges ? I watched a few videos and browsed the Internet but it is kind of complicated to grasp for me and didn't quite find a simple way.
I'm not aware of any simple methods to determine optimum gate resistance.  Most FETs and IGBTs are specified at 0-10Vgs or 0-15Vge drive.  Driving at +-12V or +-18V has a large effect on switching times.  Gate capacitance is rarely specified for negative voltages.  Best option is to check waveforms with a scope.

On the good side, gate resistance value (when bypassed by a diode) is less important for SSTC than for DRSSTC.  For SSTC, turn-off is (almost) always at relatively high current.  Gate diode makes turn-off fast, minimizing switching loss.  There is plenty of time for opposite FET/IGBT to turn on before current reverses.  So even a slow turn-on (large gate resistance) is generally fine.  10R is common for single TO220 or TO247 devices.  Should be fine for your SSTC.

Gate resistance serves a second purpose besides adding dead-time:  Reduces Vgs overshoot and ringing due to GDT leakage inductance.  Your GDT is well constructed with twisted pairs on the core and twisted lead wires.  That minimizes leakage inductance.  Even 5 ohms would likely be plenty for damping given your good GDT.

If you change to a TO247 IGBT, be careful to keep lead wires short even while bending to fit a TO220 ECB, especially emitter and collector.  Or, if you want to construct a half-bridge board for your IGBTs, here's my tutorial on making a simple low-parasitic-inductance board from either copper-clad board or copper tape:
https://highvoltageforum.net/index.php?topic=1324.msg9795#msg9795
Edit:  Oops.  Somehow was thinking IRFP460 was a TO220 device.  Actually TO247-style, so no issue with bending leads to change to IGBT.

Not likely an issue, but that IKW60N60 IGBT you selected has about twice the typical gate charge as IRFP460.  Presume your gate drive circuit can handle 2x power.  There are other IGBTs with gate charge similar to IRFP460 FET.
« Last Edit: January 24, 2023, 05:25:49 AM by davekni »
David Knierim

Offline LoOdaK

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Re: First test of the SSTC
« Reply #27 on: January 26, 2023, 12:02:14 PM »
So I got some time, I wound the new primary and tested the coil.
I was using K60H603 IGBTs.

Testing was successful, nothing blew up :D

Below is the video of the coil test and music test and a couple of photos:


New primary coil on the left and the old one on the right for comparison



Primary coils with the driver board in the middle.


Link to the test of the coil (can't include into post because it is short)
https://www.youtube.com/shorts/_DZXR-RVtt4

Music test:
https://www.youtube.com/shorts/41ZnYOcYUac


I needed to isolate secondary with some wrapping (I don't know how you call them in English). In the first video, there is a bit of corona around the primary when running almost full power, so coupling should probably be lowered slightly more. Also, there is some corona on the antenna, which should be fixed probably.

In the music test, I tried to play a faster song after this one but it was just a mess, the song is heavily distorted and song can't be recognized. What could cause that ? I'm thinking it is probably feedback and lack of shielding of the driver. I'm also considering winding the feedback transformer, how I should go about that ?
« Last Edit: January 26, 2023, 12:04:24 PM by LoOdaK »

Offline davekni

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Re: First test of the SSTC
« Reply #28 on: January 27, 2023, 05:05:40 AM »
Quote
I needed to isolate secondary with some wrapping (I don't know how you call them in English). In the first video, there is a bit of corona around the primary when running almost full power, so coupling should probably be lowered slightly more.
Coats of polyurethane epoxy are common on secondary coils.  Makes them more robust against physical abuse (bumps etc.) and provides insulation.  I've seen electrical tape work too.  Insulation is best either tightly adhered to secondary (as with epoxy coating) or spaced away by at least several mm.  A tiny (but non-zero) gap can trap any remaining corona, increasing rate of damage to insulating layers (coil varnish and inside of added insulating layer).
Hopefully you will get some other answers and suggestions for insulation.

Quote
Also, there is some corona on the antenna, which should be fixed probably.
Make a loop at end of antenna, or better a smooth ball.  Reduces local field strength.  Antenna will work fine inside a capped plastic pipe or other insulation too.

Quote
In the music test, I tried to play a faster song after this one but it was just a mess, the song is heavily distorted and song can't be recognized. What could cause that ? I'm thinking it is probably feedback and lack of shielding of the driver.
Difficult to tell without scope captures.  Shielding issues seem unlikely to be different between song speeds.  Oscillation startup time might be an issue, or the remaining charge on capacitors connected to return side of secondary.

Quote
I'm also considering winding the feedback transformer, how I should go about that ?
There's plenty of DRSSTC feedback current transformer (CT) examples on the forum.  Most are two stages.  Only one stage is needed for SSTC secondary feedback.  Just wind CT secondary around core, 80 turns if you want to keep that ratio.  Then one turn for CT primary (just wire passing through core for toroid core).
David Knierim

Offline LoOdaK

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Re: First test of the SSTC
« Reply #29 on: January 28, 2023, 03:29:09 AM »
Quote
Coats of polyurethane epoxy are common on secondary coils.  Makes them more robust against physical abuse (bumps etc.) and provides insulation.  I've seen electrical tape work too.  Insulation is best either tightly adhered to secondary (as with epoxy coating) or spaced away by at least several mm.  A tiny (but non-zero) gap can trap any remaining corona, increasing rate of damage to insulating layers (coil varnish and inside of added insulating layer).
Hopefully you will get some other answers and suggestions for insulation.
I actually have two coats of polyurethane varnish on the secondary. When playing music I didn't see any corona forming.


Quote
Difficult to tell without scope captures.  Shielding issues seem unlikely to be different between song speeds.  Oscillation startup time might be an issue, or the remaining charge on capacitors connected to return side of secondary.
Hmm, probably oscillation startup, something tells me that's the reason :) I hope I will soon get a scope so I could see the waveforms.


Quote
There's plenty of DRSSTC feedback current transformer (CT) examples on the forum.  Most are two stages.  Only one stage is needed for SSTC secondary feedback.  Just wind CT secondary around core, 80 turns if you want to keep that ratio.  Then one turn for CT primary (just wire passing through core for toroid core).
Thanks, I have some spare N30 cores laying around so I will probably make one for the test. Transformer feedback seems like a better solution to me than antenna feedback.

Offline davekni

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Re: First test of the SSTC
« Reply #30 on: January 28, 2023, 04:44:51 AM »
Quote
I actually have two coats of polyurethane varnish on the secondary. When playing music I didn't see any corona forming.
Sounds good.  If air-dry varnish, that will be much thinner than can be obtained with polyurethane epoxy (as used for glossy table tops etc.).  My DRSSTC initially had racing spark issues.  Besides reducing coupling a little, I increased epoxy coating from 2 to 7 layers, about 1mm per layer.  Doubt you need to go anywhere near that extreme.
David Knierim

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Re: First test of the SSTC
« Reply #30 on: January 28, 2023, 04:44:51 AM »

 


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post Re: Help Sourcing or Debugging My Small HV Module
[Transformer (Ferrite Core)]
michaelrcolton
February 08, 2024, 07:04:07 PM
post ESAB Bantam TBH 140 Welder Restoration
[Laboratories, Equipment and Tools]
Mads Barnkob
February 08, 2024, 06:47:35 PM
post Re: Anyone used iCCFL.com?
[Transformer (Ferrite Core)]
FPS
February 08, 2024, 12:27:47 AM
post Re: PLL "IHFSSTC" concept and schematic
[Solid State Tesla Coils (SSTC)]
Anders Mikkelsen
February 07, 2024, 09:49:11 PM
post Re: Anyone know of a good variable driver?
[Beginners]
NyaaX_X
February 07, 2024, 04:48:02 PM
post Re: Anyone know of a good variable driver?
[Beginners]
FPS
February 07, 2024, 08:17:37 AM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
Terry
February 06, 2024, 10:51:35 PM
post Re: OCXO Reference devolopment - or a story about scaleability
[Radio Frequency]
Mads Barnkob
February 06, 2024, 07:29:29 PM
post Re: Anyone used iCCFL.com?
[Transformer (Ferrite Core)]
MRMILSTAR
February 05, 2024, 05:18:33 AM
post Re: Anyone know of a good variable driver?
[Beginners]
Mads Barnkob
February 04, 2024, 09:16:25 PM
post Re: PLL "IHFSSTC" concept and schematic
[Solid State Tesla Coils (SSTC)]
davekni
February 04, 2024, 09:13:36 PM
post Anyone used iCCFL.com?
[Transformer (Ferrite Core)]
FPS
February 04, 2024, 09:00:30 PM
post Re: Anyone know of a good variable driver?
[Beginners]
FPS
February 04, 2024, 08:56:14 PM
post Re: OCXO Reference devolopment - or a story about scaleability
[Radio Frequency]
Da_Stier
February 04, 2024, 08:18:01 PM
post Re: Anyone know of a good variable driver?
[Beginners]
Mads Barnkob
February 04, 2024, 08:04:36 PM
post OCXO Reference devolopment - or a story about scaleability
[Radio Frequency]
Da_Stier
February 04, 2024, 07:56:55 PM
post Re: PLL "IHFSSTC" concept and schematic
[Solid State Tesla Coils (SSTC)]
Lucasww
February 04, 2024, 08:45:53 AM
post Anyone know of a good variable driver?
[Beginners]
FPS
February 04, 2024, 12:56:52 AM
post Re: looking for a pll sstc schematic with gate driver ic.
[Solid State Tesla Coils (SSTC)]
yourboi
February 03, 2024, 07:01:12 PM
post Re: SSTC bus inductance
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
February 03, 2024, 08:04:29 AM
post Re: SSTC bus inductance
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
February 03, 2024, 06:01:12 AM
post Re: is there a standard pinout of optical audio output connectors?
[Electronic Circuits]
Rafft
February 02, 2024, 05:04:44 PM
post SSTC bus inductance
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
February 02, 2024, 08:34:56 AM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
klugesmith
February 01, 2024, 07:03:41 PM
post Does anyone have a 3d print form for a spiral primary on 4" pvc?
[Solid State Tesla Coils (SSTC)]
yourboi
February 01, 2024, 06:23:45 PM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
Mads Barnkob
February 01, 2024, 07:53:53 AM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
klugesmith
January 31, 2024, 11:43:32 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
Ranni81
January 31, 2024, 08:03:40 PM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
Hysteresis
January 31, 2024, 03:34:48 PM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
January 31, 2024, 05:08:10 AM
post Re: How much power?
[Spark Gap Tesla Coils (SGTC)]
Mads Barnkob
January 30, 2024, 10:17:45 PM
post How much power?
[Spark Gap Tesla Coils (SGTC)]
Terry
January 30, 2024, 08:07:39 PM
post Ultrasonic Plastic Welding experiments with TA-40CS transducer
[Transformer (Ferrite Core)]
davekni
January 28, 2024, 11:37:30 PM
post Re: is there a standard pinout of optical audio output connectors?
[Electronic Circuits]
yourboi
January 28, 2024, 03:07:12 AM
post Re: First time DRSSTC Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Saattvik24
January 27, 2024, 02:27:29 PM
post Re: Lathe Restauration
[General Chat]
Mads Barnkob
January 27, 2024, 01:26:34 PM
post Re: Determine output voltage of DRSSTC
[General Chat]
Mads Barnkob
January 27, 2024, 01:15:51 PM
post Re: is there a standard pinout of optical audio output connectors?
[Electronic Circuits]
Mads Barnkob
January 27, 2024, 01:13:29 PM
post Determine output voltage of DRSSTC
[General Chat]
Pavol
January 27, 2024, 11:35:35 AM
post is there a standard pinout of optical audio output connectors?
[Electronic Circuits]
yourboi
January 27, 2024, 01:47:13 AM
post Re: First time DRSSTC Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
AstRii
January 26, 2024, 11:26:11 PM
post Re: First time DRSSTC Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Saattvik24
January 26, 2024, 08:24:30 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Netzpfuscher
January 26, 2024, 05:19:18 PM
post Re: Anyone had success using analogue/digital HV panel meters?
[Beginners]
MRMILSTAR
January 26, 2024, 04:28:38 PM
post Re: Anyone had success using analogue/digital HV panel meters?
[Beginners]
Luca c.
January 26, 2024, 03:34:10 PM
post Re: Anyone had success using analogue/digital HV panel meters?
[Beginners]
FPS
January 26, 2024, 11:49:48 AM
post Re: Anyone had success using analogue/digital HV panel meters?
[Beginners]
TizianoBll
January 26, 2024, 11:04:37 AM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
January 26, 2024, 06:26:58 AM

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