QCW questions

[davekni]

Secondary Resonant freq with 2 topload is 343.6KHz (JTC) ....... freq drop from 420KHz to 343KHz

What material is your "GND BASE REFERENCE" plate made of?  (The plate at the bottom of your coil.)  If metal (conductive), that will reduce both primary and secondary inductances as it blocks AC magnetic field.  Also, does anyone know if JavaTC includes such inductance reduction for the secondary coil due to top-load proximity?  Does your primary winding extend all the way from bottom to top?  Or, are there gap(s)?

[Rafft]

I have re-measured actual resonant frequencies of PRI and SEC

Secondary with toroid & cylinder topload, coil/topload removed from base
======================================
based on JavaTC = 353.3KHz Secondary and topload/s only
based on JavaTC = 343.6KHz sec/toploads/pri/mmc whole system
"series resonance test" signal gen / 10k res = 347KHz
"series resonance test" signal gen / 10k res =  289KHz w/simulated streamers , 40" wire upward

Primary with MMC(14.5nF) in parallel , Secondary coil removed
=======================================
6T = 410KHz most spark length I get
7T = 382KHz
8T = 340KHz

Primary with MMC(14.5nF) in parallel , Secondary coil INSTALLED
=======================================
6T = 410KHz
6T = 406KHz with simulated streamer

6T = 456KHz Secondary Coil GNDed, no streamers
6T = 447KHz Secondary Coil GNDed, WITH simulated streamers

What material is your "GND BASE REFERENCE" plate made of?

the white plate is plastic(from printer paper tray). rest of the thing/s holding the assembly, is wood. only large metal are the long bolts/nuts & aluminum tube(bolt support). there are no metal screen or plate to protect the electronics underneath(yet).

Does your primary winding extend all the way from bottom to top?  Or, are there gap(s)?

its elevated half an inch from "gnd base ref" . it has small gaps inbetween, zip ties near the 6T &T taps.

Your waveforms look more like a single resonant system to me. Scan the primary resonant circuit and see if you get two resonant frequency peaks.

ok, I assume youve built QCW before (?) . I have no idea how they would look like . 'these' waveforms are usually what I see online but sure, I will recheck it later 

[davekni]

Great data!  Thank you.

6T = 456KHz Secondary Coil GNDed, no streamers
6T = 447KHz Secondary Coil GNDed, WITH simulated streamers

Does this refer to bottom of secondary grounded (normal operation condition), or top also grounded (secondary shorted)?  I'm guessing the former.  If you took a measurement with shorted secondary, that would allow calculating coupling factor between primary and secondary.

Numbers look reasonable.  Here's a quick AC LTSpice simulation with your coil parameters.  I used slightly higher primary inductance based on 410kHz and 14.66nF.  Coupling factor is a guess at 0.32.  What does JavaTC say for coupling with your latest geometry?  Red is without arc.  Green is with arc.  Arc capacitance is derived from your frequency measurements with 40" wire.  Arc resistance is a guess.


I did try changing to your higher-inductance primary.  Indeed, arc voltage was slightly lower that way.  Only 1.5dB or so.  That is with constant input voltage.  With higher primary inductance, current is lower.  If your H-bridge were limited by current rather than voltage, the higher inductance 8T primary would likely perform better.

[Duane B]

I have re-measured actual resonant frequencies of PRI and SEC

Secondary with toroid & cylinder topload, coil/topload removed from base
======================================
based on JavaTC = 353.3KHz Secondary and topload/s only
based on JavaTC = 343.6KHz sec/toploads/pri/mmc whole system
"series resonance test" signal gen / 10k res = 347KHz
"series resonance test" signal gen / 10k res =  289KHz w/simulated streamers , 40" wire upward

Your waveforms look more like a single resonant system to me. Scan the primary resonant circuit and see if you get two resonant frequency peaks.

ok, I assume youve built QCW before (?) . I have no idea how they would look like . 'these' waveforms are usually what I see online but sure, I will recheck it later 

No, I have not built QCW before. I don't even know what QCW stands for. I assume the CW is for Continuous Wave, but I have no idea what the Q is for. Maybe I shouldn't have contributed to this post. I thought I might be able to help from what other experience I have had. Your waveforms, re-posted here, reminded me of a single resonant system. The current waveform is the exact thing you get with driving a single resonant system. The hump you see in the beginning transient indicates that the frequency is slightly off resonance. If it were in resonance the current would rise to a maximum and stay at maximum until the driving source stops. Again, this reminds me of a single resonant system.



As far as adding a 40" wire to simulate a streamer, I say that you are only adding capacitance to the secondary and by no means is it simulating a streamer, not by a long shot! I still stand by what I said in my branch off post: the supposed capacitance of the streamer is not changing the frequency.

[Duane B]

David, I must start out by saying that I have the greatest respect for you. And I have never used LT Spice before. However, I think you have a problem with your simulated diagram. If I were to draw this diagram it would not have the streamer load as indicated. It would be a secondary coil in series with a resistor in series with the top load capacitance, and that is it (a voltage source in series with an inductance in series with a resistance in series with a capacitance). The resistor is a dynamic resistor. It would be difficult to make calculations with this resistor because it changes resistance with and without sparks, and with how much energy is delivered to the spark. One thing is certain though, there must be a resistor in series with the secondary inductance and capacitance!

I suppose you could use a Thevenin's or Norton's equivalent circuit, and simulate with either a series or parallel circuit, but you diagram has components both in series and parallel.

[davekni]

David, I must start out by saying that I have the greatest respect for you. And I have never used LT Spice before. However, I think you have a problem with your simulated diagram. If I were to draw this diagram it would not have the streamer load as indicated. It would be a secondary coil in series with a resistor in series with the top load capacitance, and that is it (a voltage source in series with an inductance in series with a resistance in series with a capacitance). The resistor is a dynamic resistor. It would be difficult to make calculations with this resistor because it changes resistance with and without sparks, and with how much energy is delivered to the spark. One thing is certain though, there must be a resistor in series with the secondary inductance and capacitance!

Thank you for the compliment.
I did omit the wire resistance of secondary coil.  I could add that for a small change to the result.  The top-load capacitance does not have any significant series resistance.  It is just capacitance to ground.  Before breakout, Q is quite high.  JavaTC estimates that Q, 196 in your case.  That Q is not infinite because of secondary winding resistance (a bit higher than DC resistance due to skin and proximity effects).
Yes, arc load is dynamic.  I simulated some random place towards the end of the ramp with a long arc.  Power dissipation in the arc is not due to resistance in series with top-load capacitance.  It is from arc resistance.  Arc current returns to ground through the arc's capacitance.  That is the added 4.7pF in my simulation.  The only way the arc conducts current is through its capacitance, not through top-load capacitance.
Of course, reality is always a bit more complex than models.  Arc capacitance and resistance are both distributed along the arc.  And there is some capacitance from arc sections to the top load as well as to ground.  Picture more of a linear network of series resistors with a capacitor from each junction to ground, and capacitors across the resistors.  I have made some arc models with more than one resistor and one capacitor.  Don't have enough real-world data to know what values to use.  The simple single resistor and capacitor version can match basic arc parameters (power dissipation and secondary frequency shift).
Hope that makes things more clear.  Please feel free to question again if not.  I certainly do make mistakes.

BTW, here are a few links from this forum that discuss arc load modeling:
https://highvoltageforum.net/index.php?topic=670.msg4474#msg4474
https://highvoltageforum.net/index.php?topic=626.msg4107#msg4107
https://highvoltageforum.net/index.php?topic=1073.msg7715#msg7715
https://highvoltageforum.net/index.php?topic=798.msg9265#msg9265

[Duane B]

Dave, thanks for your description of arc loading, and for the links for more information. I will study the links and if I have more questions I will post to another thread or start a new topic. I do not want to hijack this thread any more than I have.

[Rafft]

David

Thanks for the simulations

Does this refer to bottom of secondary grounded (normal operation condition)

this exactly

If you took a measurement with shorted secondary, that would allow calculating coupling factor between primary and secondary.

yes, tried it on my other cheap LCR meter, 0.3uH reading. JTC shows 0.31x something. it has low decimal count unlike my DIY(but un-useable with secondary coil in place)




I have learned & finalized my hardware/values and settle for 450KHz operating freq.

Ive recorded a video outdoors. funny thing is "squeel" along with the spark at 300Vdc. none at lower voltages. I will recheck hardware again(maybe loose wiring)

time for a full-bridge, proper toroid topload (4"dia), and bigger bulk cap), newer primary for more k. QCW is just another level of beast 

cheers
Ralph

[davekni]

Ive recorded a video outdoors. funny thing is "squeel" along with the spark at 300Vdc. none at lower voltages. I will recheck hardware again(maybe loose wiring)

Nice performance and video!
My high-frequency hearing (2kHz and up) is down ~30dB, so I'm not hearing a squeel.  However, the sound is sharper on some pulses, like a sudden change in amplitude rather than a linear ramp.  Have you managed to scope anything at 300V to look for differences between the normal and sharp sounding pulses?

[Rafft]

David, Thanks for the compliment.

Have you managed to scope anything at 300V to look for differences between the normal and sharp sounding pulses?

unfortunately I havent saved the waveform(270v bus). too bad. anyways, it was just an intermittent connection from secondary coil "gnd", to outside GND. it was not a solid connection. now Ive soldered the "start" end of coil, to a wire going outside for GND connection. judging from some QCW vids of others, it sounded like the arc was hitting/getting a ground strike.

currently waiting for my 2200uF x 3pcs to arrive.I HOPE this increases arc length  else this is the max arc length the (small-ish? 3" x 4.8")coil can do

im also checking whats the difference with upper pole and lower pole operation.

Code: [Select]

my secondary[reference]: Series resonance test
347KHz with topload
282KHz with topload and 40" wire loaded

**video above shows straight arcs at 454KHz(2.2uS), way above secondary/topload resontant freq.

***Ive tried higher cap value for MMC (same primary TAP, MMC 27nF) ->> 279KHz(3.58uS), Very Clean Iprim, arcs are branchy now, this is close to the secondary(loaded) res freq. sorry no videos. it was just a quick test if it even arcs at that low freq

**** NEXT to try 22nF (LC res calculation) ->> 384KHz, slightly above secondary resonant freq



for QCW, any idea what is the difference between upper pole and lower pole operation aside from the branchy and straight arcs?


just a grab from your post, the green solid line. does the lower peak suggest the lower pole?? and higher peak as upper pole?? if so, it makes sense to my calculations 

[davekni]

unfortunately I havent saved the waveform(270v bus). too bad. anyways, it was just an intermittent connection from secondary coil "gnd", to outside GND. it was not a solid connection. now Ive soldered the "start" end of coil, to a wire going outside for GND connection. judging from some QCW vids of others, it sounded like the arc was hitting/getting a ground strike.

Only reason for a waveform was to figure out a cause.  Great job figuring out the issue quickly.  No need for waveforms.

for QCW, any idea what is the difference between upper pole and lower pole operation aside from the branchy and straight arcs?

I don't have any real QCW experience.  My knowledge is from my failed low-frequency experiment, simulations, and reading this forum.  Hopefully others with real experience will share details.  (Also, search the forum for QCW and upper/lower pole.  There is information here.)

just a grab from your post, the green solid line. does the lower peak suggest the lower pole?? and higher peak as upper pole?? if so, it makes sense to my calculations 

Yes, green is with simulated arc load.  Left peak is lower pole.  Right (higher) peak is upper pole.  Yes, upper pole generates 12dB higher arc power for this simulated load and constant bridge voltage.

[Rafft]

Yes, green is with simulated arc load.  Left peak is lower pole.  Right (higher) peak is upper pole.  Yes, upper pole generates 12dB higher arc power for this simulated load and constant bridge voltage.

David, awesome! didn't think LTspice could "see" those poles. makes for the PRIMARY resonant freq "hunting" faster. I do have some knowledge using LTspice but with -simple- circuits only, and NOT tesla coils.

**what where your input parameters for this?

**could you maybe post here your file?

**screenshot for simulation tab? etc etc

**small tutorial perhaps?   

this would really prove helpful once I make another primary coil (conical) to increase coupling between pri/sec and a 4"dia toriod(to make it look MORE of a traditional tesla coil). all I'm doing is just getting the sec loaded/unloaded resonant freq  and add 60 - 110KHz (from sec unloaded), for the primary resonance.

 

[Uspring]

for QCW, any idea what is the difference between upper pole and lower pole operation aside from the branchy and straight arcs?

I believe the branchiness of arcs to be the result of a low operation frequency. It does not depend on the choice of poles. Here's a short Q&A regarding poles:

1. What are poles?

Poles are resonant frequencies. A single tank, e.g. has a single resonant frequency, which can be calculated from its capacitance and inductance. Two tanks have 2 res frequencies, which each can be calculated the same way. If you bring the tanks in proximity, so that the magnetic fields of the coils begin to overlap, the system becomes coupled and the resonant frequencies of the system change. Initially, the lower pole is the lower of the 2 tanks res frequencies and the upper pole the upper one. Once the tanks are coupled, the lower pole will move downward in frequency and the upper pole upward. The larger the coupling is, the more the poles will move away from the tanks original res frequencies.
You can see this in Davids diagram (red lines). The secondaries resonant frequency is 347 kHz and the primary res frequency is 410 kHz. The poles are at 320 kHZ and 465 kHz. For the arc loaded coil (green lines), the frequencies are shifted somewhat downward due to the arcs capacitance lowering the secondary res frequency.

2. At what frequency does my coil run?

Standard drivers usually employ zero current switching, which is gentle on the bridge transistors. This means, that primary voltage and primary current are in phase. In order to produce a diagram I've shamelessly stolen the parameters from Davids simulation. It shows the primary current amplitude and its phase wrt the input voltage.

The green dotted line (phase) crosses 0 degrees at 452 kHz, which is close to the observed frequency. Note, that there is only one zero crossing. This is due to the large arc load and/or to a large difference between the tanks res frequencies.
You can read off this diagram also the gain at the operating frequency. This is 3 dB, which means a primary current of 1.4 A for each Volt of input voltage. With this information you can match your bridges output capabilities to the coil.

Here is another diagram, where I have increased the primary MMC to 27 nF.

You can see now 3 zero crossings of the phase at 263, 293 and 359 kHz. All 3 are, in principle, zero current switching frequencies, but the center one has an inbuilt instability. Useable are really only the upper and lower frequencies, which correspond to the peaks (i.e. poles) in the current amplitude line. Generally, with zero current swutching, the DRSSTC drivers will start with the primary res frequency and then end up at the frequency of the nearest pole. This turns out to be the lower pole in this case. It was the upper pole in the previous diagram.

At the lower frequency, where you are running with the 27n cap, the current amplitude is now at -8dB, i.e. 0.4 A per input Volt, so current draw is much lower than in the previous example. I'd expect considerably shorter arcs, if you haven't increased input voltage. And the shorter arc is probably the reason, why your measured operating frequency of 279 kHz is somewhat above the calculated one of 263kHz. Since I did not change Davids arc loading circuit, the calculated frequencies are a bit too small. Smaller arcs have less capacitance and don`t decrease the res frequencies as much.

3. What is a big primary/secondary fres difference?

so in summary:
Secondary Fres = 343.6KHz
Primary Fres = 435KHz
91KHz difference. IS this a BIG or small difference? is this NORMAL ? I mean the freq difference. I was thinking maybe a 10-20KHz would do, but I guess it needs bigger difference cuz its higher freq compared to DRs in the 50-150KHz (?)

That depends mainly on the coupling factor. Large frequency differences imply bad primary -> secondary power transfer efficiencies. But this can be compensated by a large coupling. QCWs often have a large coupling, while that of standard DRSSTCs is much lower. So QCWs can live with larger frequency differences.
Large couplings in standard DRSSTCs are difficult due to racing arcs and flashovers. QCWs often are built ot produce sword arcs. These arcs need to be slowly ramped up and run at high frequencies. Both of this makes them create relatively low voltage arcs. And this simplifies achieving a high coupling without undesirable side effects.

[Rafft]

Uspring

A big thanks for the explanations.  that explains most of what I'm seeing on my coil setup.


today's hardware update:

Epcos 2200uF 350Vdc bulk caps (6,600uF in total)


I Have gone Full-bridge of IRG4PC50FD. heatsink is from an old HDD


my coil. ditched the CAN top, replaced back to using 2 small toroids, so it looks more like a tesla coil


secondary with 2 toploads = 379KHz , 310KHz loaded with 36" wire (measured using sig gen and scope)
Primary is 11.8uH(8th tap) 9.9uH(7th) 7.8uH(6th) and MMC is 16.5nF(4s3p of 22nF)
k = 0.39
sec 3.2"D x 4.85"H #33 awg 683T 610KHz (jtc)
topload 1.3" 6.4"  423KHz (jtc) + 1.3" x 6.8" 389KHz (jtc)


calculating upper and lower pole
Fupper = F/sqrt(1-k)
Flower = F/sqrt(1+k)

Fupper = 485KHz
Flower = 350KHz

Ive tested 8T = 297KHz  , 7T = 431KHz , 6T = 450KHz, 6T giving the longest spark. I have only tested with 180Vdc(indoors) and it has already surpassed(more or less) the spark length compared to half-bridge on 250Vdc.

now my question is, my phase lead is different now , is this GOOD or BAD?


also, when I switch between 7T and 8T, it locks on to the upper pole(431KHz) and lower pole(297KHz), respectively. its like a toggle switch.. again , is this normal??  I had to take a second measurement just to see that I wasnt dreaming or making stuff up 


cheers
Ralph

[davekni]

I lost track of this thread, so here's some belated answers in case such is still useful.

David, awesome! didn't think LTspice could "see" those poles. makes for the PRIMARY resonant freq "hunting" faster. I do have some knowledge using LTspice but with -simple- circuits only, and NOT tesla coils.

Any of the spice-type simulators will show poles of coupled resonators using an AC frequency sweep.  Circuit isn't too complex, as you can see from the schematic I posted (as a JPG image).

**what where your input parameters for this?

All parameters are shown on the spice schematic I posted.  The simulation is for 1Vpeak drive as per the "AC 1" label on voltage source V1.  This could be changed to actual bridge output voltage.  Result would shift the plot in dB up (scale output), but not change shape at all.  R2 is a guess at total resistance of bridge IGBTs and primary coil, 0.1 ohms in my example.  L3 is a guess at wiring inductance from bridge through MMC to primary.  C2 is MMC.  L1 is primary coil, 10uH.  L2 is secondary, 19.68mH.  Directive "k12 l1 l2 0.32" defines the primary-to-secondary coupling factor.  C3 is top load capacitance, 10.7pF here.  C4 and R1 are a guess at arc loading for some point later in the ramp.  The "ac lin 4k 200k 600k" directive tells LTSpice to sweep frequency linearly from 200kHz to 600kHz with 4000 steps.  The "step param arc list 4.7p 10f" runs the simulation twice, first with 4.7pF for arc capacitance, second with 10fF for arc capacitance.  10fF is approximately 0, but avoids the issues with 0 value components.

**could you maybe post here your file?

Here's the LTSpice schematic file in ZIP format, as native LTSpice files are not accepted for posting here.
See end of this post for the file.  Appears that only JPG images are allowed in-line with text.

**screenshot for simulation tab? etc etc

Not sure if this is what you are after.  Here's a screen shot of the entire LTSpice window running this simulation:

**small tutorial perhaps?   

Hopefully the explanation below your first question covers most of the details.  Unzip the "sstc_ac1.asc" file and double-click it to execute it with LTSpice.  Click the run symbol (person running), then click on node "vo2" in the schematic to plot top-load voltage.

now my question is, my phase lead is different now , is this GOOD or BAD?

I presume the yellow trace is one side of H-bridge output.  What is the cyan trace?  An antenna?  If it is primary current, something is strange.  It appears to be switching at roughly peak current, not just before zero.  Wouldn't expect you to get much current if voltage is being driven almost 90 degrees out-of-phase with current.

also, when I switch between 7T and 8T, it locks on to the upper pole(431KHz) and lower pole(297KHz), respectively. its like a toggle switch.. again , is this normal??  I had to take a second measurement just to see that I wasnt dreaming or making stuff up 

Although I've never actually ran anything at the upper pole yet, I think this fits LTSpice simulations of such when approximating a UD2.7-style driver.  After you get comfortable with the one AC simulation here, I can dig up my transient (time) simulation of a simplified H-bridge into DRSSTC.

[Rafft]

David,

thanks. will have a go at that LTspice later 

I presume the yellow trace is one side of H-bridge output.  What is the cyan trace?  An antenna?  If it is primary current, something is strange.  It appears to be switching at roughly peak current, not just before zero.  Wouldn't expect you to get much current if voltage is being driven almost 90 degrees out-of-phase with current.

Yellow is Full-bridge output. Cyan is primary current (3rd CT). this happened when I switched from Half-bridge to Full-Bridge.

maybe probe for bridge( is reversed?)

btw, I have changed the variable inductor 14-50uH(old ckt) to 6-24uH(current ckt)...burden still the same 51R 3W(carbon comp)... could this smaller L affect the phase lead? but I do remember using THIS value while it was still in half-bridge, and it worked  as it should. or is this value too low for 250KHz-450KHz operation?

how is the phase lead inductor+Resistor working? is it when -in resonance- with that freq that it "shifts it"?

Although I've never actually ran anything at the upper pole yet, I think this fits LTSpice simulations of such when approximating a UD2.7-style driver.  After you get comfortable with the one AC simulation here, I can dig up my transient (time) simulation of a simplified H-bridge into DRSSTC.

what I meant was this:

secondary/topload/s = 379KHz unloaded, according to JTC
Upper/Lower pole = 485KHz/321KHz
k = 0.39

calculated :                                                     actual coil operation:
8T(11.8uH) & 4s3p(16.5nF) = 360.7KHz            298KHz
7T(9.9uH)                          = 394KHz               431KHz
6T(6.8uH)                          = 443.6KHz            450KHz

numbers in BOLD has really big freq difference. 7T is upper pole and when changing to 8T, it sort of flips down directly to lower pole. I still remember you said thats how the UD works, in lower pole.

everything with this full bridge is wierd. lol. back when I was in half-bridge, coil wont start unless I give the buck a standby voltage of around 40-50Vdc, but now that its in full-bridge, I can start the coil EVEN with buck output at almost 0v initial (and with a 0v - max volt rise RAMP, I get a "solid" spark. solid like SOLID..not hissy or hazzy etc etc call it a lovely sword spark if you will)
correction: it STILL needs that 'wick' but minimal voltage only. when I set the 'wick' to minimum(or zero), coil almost always misses to spark.


some javaTC data if you want

Code: [Select]

J A V A T C version 13.6 - CONSOLIDATED OUTPUT
18/02/2022, 10:28:07

Units = Inches
Ambient Temp = 68ºF

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
1.6 = Radius 1
1.6 = Radius 2
1 = Height 1
5.85 = Height 2
683.1 = Turns
33 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
2.9 = Radius 1
2.7 = Radius 2
1 = Height 1
3.35 = Height 2
8.462 = Turns
0.079 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.0165 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
349.83 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
4.85 [inch] = Length of Winding
140.8 [inch] = Turns Per Unit
0.00002 [inch] = Space Between Turns (edge to edge)
572.3 [ft] = Length of Wire
1.52 [:1] = H/D Aspect Ratio
117.4373 [Ohms] = DC Resistance
39257 [Ohms] = Reactance at Resonance
0.09 [ lbs] = Weight of Wire
17.86 [mH] = Les-Effective Series Inductance
19.29 [mH] = Lee-Equivalent Energy Inductance
19.032 [mH] = Ldc-Low Frequency Inductance
11.589 [pF] = Ces-Effective Shunt Capacitance
10.73 [pF] = Cee-Equivalent Energy Capacitance
18.142 [pF] = Cdc-Low Frequency Capacitance
4.68 [mils] = Skin Depth
8.078 [pF] = Topload Effective Capacitance
244.5588 [Ohms] = Effective AC Resistance
161 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
365.34 [kHz] = Primary Resonant Frequency
4.25 [% low] = Percent Detuned
85 [deg °] = Angle of Primary
12.41 [ft] = Length of Wire
20.77 [mOhms] = DC Resistance
0.2 [inch] = Average spacing between turns (edge to edge)
1.057 [ inch] = Proximity between coils
0 [inch] = Recommended minimum proximity between coils
11.502 [µH] = Ldc-Low Frequency Inductance
0.018 [µF] = Cap size needed with Primary L (reference)
0 [µH] = Lead Length Inductance
182.911 [µH] = Lm-Mutual Inductance
0.391 [k] = Coupling Coefficient
0.127 [k] = Recommended Coupling Coefficient
2.56 [half cycles] = Number of half cycles for energy transfer at K
3.16 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=1.3, major=6.4, height=7, topload
Toroid #2: minor=1.3, major=7, height=8.3, topload


Code: [Select]

units=0,
ambient=0,
s_ws=0,
s_Al=0,
p_ws=1,
p_Al=0,
p_ribbon=0,
temp=68,
g_radius=0,
w_radius=0,
ceil_height=0,
s_radius1=1.6,
s_radius2=1.6,
s_height1=1,
s_height2=5.85,
s_turn=683.1,
s_wd=33,
p_radius1=2.9,
p_radius2=2.7,
p_height1=1,
p_height2=3.35,
p_turn=8.462,
p_wd=0.079,
p_vwidth=0,
p_rthick=0,
Cp_uF=0.0165,
Lead_Length=0,
Lead_Diameter=0,
desired_k=0,
t.inner=1.3,
t.outer=6.4,
t.height=7,
TT=true,
TG=false,
t.inner=1.3,
t.outer=7,
t.height=8.3,
TT=true,
TG=false,
x_Vin=0,
x_Vout=0,
x_Iout=0,
x_Hz=0,
x_Vadjust=0,
x_ballast=0,
rsg_ELS=0,
rsg_ELR=0,
rsg_rpm=0,
rsg_disc_D=0,
rsg_ELR_D=0,
rsg_ELS_D=0,
stat_EL=0,
stat_EL_D=0,
stat_gap=0,
SPE=true,
RGE=false


edit:
been doing the LTSpice sim. Ive edited the primary inductance and MMC. secondary and topload. and the coupling as well. values used was from above jtc. I hope its correct?

btw HOW do you make inductors (like L1 and L2) be coupled together? this is based on the directive "k12 l1 l2 0.32", right?  though I dont understand what 'k12' is.



edit2:
on second thought (regarding strange waveform between bridge and Iprim), I will just have to RE-wind that GDT. I could have messed up the wiring(probably) ... it was made 12yrs ago w/c never got used. and this is my 1st time using full-bridge..if memory serves me right. better late than never 


=========================
edit3:
I have replaced the big GDT with my smaller toroid(wound with 5-filar, 100uH), yellow (bridge) &  cyan (Iprim)

result still the same... tried with the variable inductor and the result below

testing with 50Vdc bus(DR only) , with slug removed(6uH) on the input LC


with slug installed, around 24uH

[davekni]

Yellow is Full-bridge output. Cyan is primary current (3rd CT). this happened when I switched from Half-bridge to Full-Bridge.

maybe probe for bridge( is reversed?)

Probe reversal would shift the waveform by 180 degrees, so not explain a 90 degree offset.  It's surprising that you can get much primary current at all with almost 90 degree phase shift.  Perhaps the phase shift is closer to 0 (or 180) earlier in the burst, allowing primary current to build.

btw, I have changed the variable inductor 14-50uH(old ckt) to 6-24uH(current ckt)...burden still the same 51R 3W(carbon comp)... could this smaller L affect the phase lead? but I do remember using THIS value while it was still in half-bridge, and it worked  as it should. or is this value too low for 250KHz-450KHz operation?

edit3:
I have replaced the big GDT with my smaller toroid(wound with 5-filar, 100uH), yellow (bridge) &  cyan (Iprim)

result still the same... tried with the variable inductor and the result below

testing with 50Vdc bus(DR only) , with slug removed(6uH) on the input LC

It looks like delay through the driver and H-bridge is more than 90 degrees.  That can work with feedback inverted (CT polarity, GDT polarity, etc.).  With more phase-lead (24uH), voltage and current are almost 90 degrees off (not desired).  With less phase-lead (6uH), voltage is delayed (not advanced as much), so closer to current phase.
The change to full-bridge could be related to this.  Twice the load on driver and GDT will slow down gate waveforms (add delay).

calculated :                                                     actual coil operation:
8T(11.8uH) & 4s3p(16.5nF) = 360.7KHz            298KHz
7T(9.9uH)                          = 394KHz               431KHz
6T(6.8uH)                          = 443.6KHz            450KHz

After some thought, I have experienced this on my DRSSTC.  When arc loading capacitance gets high enough (long arcs), it reduces secondary frequency below primary frequency.  I have scope traces showing this transition from lower-pole to upper-pole operation at the end of a long arc enable pulse:
https://highvoltageforum.net/index.php?topic=798.msg9200#msg9200
Difference is that frequency remains similar.  Mostly the pole locations are moving due to arc capacitance.

https://highvoltageforum.net/index.php?topic=798.msg9200#msg9200

Phase lead of UD2.7 (L+R series circuit) works whether at resonance or not.  You can demonstrate this in LTSpice with a very simple circuit.  Current source (instead of voltage source) simulated CT output.  Feed that current source through a series inductor and resistor.  Plot voltage of the current source (voltage of series R+L) over a sweep of frequencies.  Phase lead does change some with frequency, but no sudden change around Tesla coil resonances.  (There is no capacitor in this phase-lead circuit, so that circuit is not itself resonant.)

btw HOW do you make inductors (like L1 and L2) be coupled together? this is based on the directive "k12 l1 l2 0.32", right?  though I dont understand what 'k12' is.

Yes, just add the "k" statement and inductors are coupled.  "k12" is an arbitrary label, but must start with "k" so LTSpice knows it is a coupling factor.  The two (or more) inductors that are coupled are defined by the "l1" and "l2" strings.  Those must match the instance labels of the inductors.

edit3:
I have replaced the big GDT with my smaller toroid(wound with 5-filar, 100uH), yellow (bridge) &  cyan (Iprim)

You could try the 8-filar version (four paralleled primary windings) for even lower parasitic inductance:
https://highvoltageforum.net/index.php?topic=1854.msg13949#msg13949

However, my guess is that you are running past 90 degrees of phase lag.  Rather than attempting to reduce delay, it may be better to live with that delay and perhaps add a bit more to achieve close to 180 degrees.  Slightly less than 180 is as good as the usual slightly less than 0 degrees.  Only down side is that phase will change more as frequency changes.  (I've build resonant H-bridge systems using phase lag instead of lead, though not for a Tesla coil.)

[Uspring]

secondary/topload/s = 379KHz unloaded, according to JTC
Upper/Lower pole = 485KHz/321KHz
k = 0.39

calculated :                                                     actual coil operation:
8T(11.8uH) & 4s3p(16.5nF) = 360.7KHz            298KHz
7T(9.9uH)                          = 394KHz               431KHz
6T(6.8uH)                          = 443.6KHz            450KHz

Usually the coil will operate at the lower pole, if primary fres is lower than the secondary fres and at the upper pole if primary fres is larger than the secondary fres. This is, what you see here.
If res frequencies are similar, the coil will, for a while, run at both pole frequencies. This shows up as beats in the primary current waveform.

[Rafft]

guys

Ive converted my synchro buck, to non-sync. so that instead of using 2 igbt(hi & lo), I can just use both for HI side, and a diode for low.

it all works on bench test. 10v & 20v input, with 2 2.2R 10w(wirewound) in parallel(as my load)

now in actual, I have the output LC loaded with 3kR 5w (wirewound, three 1k5w in series). DC bus is 113Vdc. when I trigger it, its in DR mode sparks(and not sword sparks).

when I connect scope probes(set to x10), spark output goes sword. If I remove probe connection, goes back to branching sparks.

Ive even used 3k9 3w(carbon comp) and 680R 5w wirewound.. still same result



ideas?


edit:
I just remembered seeing a video on ytube where he had bulbs (near the buck).. hmmm I wonder if this would work to drain the output quickly(?)

BUT why does connecting a scope probe 'fix' the ramp output? my coil is battery-powered and no connection to ac line (only scope is connected to ac line, for power)

edit2:
maybe this is the downside of being an async. compared to a sync w/c never uses any 'load' to discharge because its already being handled by the low-side switch.

edit3:
  https://4hv.org/e107_plugins/forum/forum_viewtopic.php?156071
based here (Steve Ward), maybe I just go back to synchro and use a mosfet for the lo side? better switch than an IGBT?

[davekni]

BUT why does connecting a scope probe 'fix' the ramp output? my coil is battery-powered and no connection to ac line (only scope is connected to ac line, for power)

My guess would be a change in grounding rather than a change in ramp shape.  Scope is adding a ground connection path.  If it is ramp related, I'd suspect that without scope ground something in your buck control circuit is getting confused by noise.