Author Topic: BrOdin coil - High power Big sparks!  (Read 17123 times)

Offline fh89

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BrOdin coil - High power Big sparks!
« on: February 08, 2021, 06:47:39 PM »
Specs:
  • Full bridge cm600ha-24h
  • Liquid cooled primary
  • 1000A primary current limit now 2500A
  • 12.75x48" secondary 23awg now 22awg
  • .57uF now 1.14uF mmc
  • 6800uf 16,800uF 26,800uF bus cap
  • 36x10 spun aluminum toroid
  • EVR/Philip Slawinski UD+ freewheeling driver
  • EVR polyphonic midi interrupter / Custom Philip Slawinski long pulse interrupter
  • All polycarbonate/aluminum enclosure
  • 30kW+ Pulling 180+ amps at 220V.Now 57kW draws 350A+ on 220V
  • up to 15ms on-times 17%duty cycle

Photo dump of all of my construction photos (some of these photos show mistakes that were later corrected):
https://1drv.ms/u/s!Ap7oF5iAXsqR_Q4Ll1D90VbZBSRI?e=13UIZi


Human for scale.


















15' from tip of break out point to strike target


Clamp Ammeter showing 351 Amps






Updated photos showing doubled MMC, added bus caps, extra fans, etc.

« Last Edit: November 09, 2021, 08:38:34 PM by fh89 »

Offline acobaugh

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Re: Large musical DRSSTC first light!
« Reply #1 on: February 08, 2021, 07:05:00 PM »
Looks good. Does any of the hardware in the frame get warm at all? What kind of power draw are you looking at?

Offline fh89

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Re: Large musical DRSSTC first light!
« Reply #2 on: February 08, 2021, 07:42:53 PM »
Quote
Looks good. Does any of the hardware in the frame get warm at all? What kind of power draw are you looking at?
Thanks! I have not noticed the frame hardware getting warm, but I also have not touch checked anything directly after a run. I haven't noticed any plastic discoloration or melting on the primary supports or disc yet though. Currently the max power draw is 8-9kW. I expect this will rise dramatically as I push up the on-times.
« Last Edit: February 09, 2021, 08:20:08 AM by fh89 »

Offline acobaugh

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Re: Large musical DRSSTC first light!
« Reply #3 on: February 11, 2021, 02:22:17 AM »
I take it you're not hitting your 2kA yet? Even at 360uS on time, your primary impedance might be too high to really push some current through. My DR82 coil uses a CM300 full bridge, OCD set to 1000A, peak current is around 1100A. Power draw is about 9kW, and I easily hit 11 feet.

I say you need to lower your tank impedance so you can really push some current.

Offline fh89

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Re: Large musical DRSSTC first light!
« Reply #4 on: February 11, 2021, 05:44:27 AM »
Quote
I take it you're not hitting your 2kA yet? Even at 360uS on time, your primary impedance might be too high to really push some current through. My DR82 coil uses a CM300 full bridge, OCD set to 1000A, peak current is around 1100A. Power draw is about 9kW, and I easily hit 11 feet..
Haven't made any attempt to determine primary current, but I would guess you are correct. Very nice performing coil BTW!

Quote
I say you need to lower your tank impedance so you can really push some current

Well, I am going to have to build another MMC because the current one was designed and built before I knew anything about running long on-times in freewheel mode, and the Arms is too low. What would be an ideal value for a low impedance? I'll admit my knowledge of low-impedance tank circuit design is lacking.
 
I am going to push more current by increasing on-time to 1.12ms and see how it goes first. Assuming a 2kA limit, 1.12ms (my interrupter's current maximum value, possibly to be increased later via firmware update) on-time at 48Hz (my interrupter's minimum value) gives a 5.39% duty cycle or 316Arms- way over my MMC's 70Arms rating.

I am going to rebuild a MMC for much higher rms current rating, but I am not sure what the ideal C value is. The current .57uF puts me at 5.75 primary turns.

Offline acobaugh

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Re: Large musical DRSSTC first light!
« Reply #5 on: February 11, 2021, 06:39:52 AM »
My CM300 coil runs at 38kHz with a 0.6uF MMC (5s20p array of 942C - not recommended if you're starting from scratch, but I already had most of these caps from the previous spark gap model). My CM600 coil will be between 1.25uF and 1.56uF, based on experimentation. For a coil your size, I would expect at least 0.8uF, probably closer to 1uF to be a good value, based on other similar designs. There are a bunch of tradeoffs involved, and I'm curious to see how your testing with long on times works out for spark formation. Just watch your temps. You might want to lower your OCD threshold to a known lower value just to see where your peak is at in case you don't have a means of measuring it in realtime. I don't think the UD+ will freewheel until you hit OCD. As others have said, you'll see more heat dissipation per unit time until you start freewheeling.

Check out Mads' MMC calculator here: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/
and the corresponding mmc design guide here: https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/

Is this your first DR coil?

Offline davekni

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Re: Large musical DRSSTC first light!
« Reply #6 on: February 11, 2021, 08:41:33 PM »
Yes, definitely explore behavior of your coil with longer on-times and more measurements using your existing MMC before changing.  Measuring primary current during operation would be ideal.  This can be done with an additional CT, or by scoping across the driver's feedback input resistor.  Knowing the operating frequency and current ramp-up and limiting (if any) will help in picking your next MMC capacitance.  If you are hitting 2000A for a reasonable portion of each enable pulse, then I wouldn't increase capacitance.

Does your controller have a single-shot mode?  I think most do.  I'd use that first for long-enable-pulse testing before running at 48Hz.  5% duty cycle will likely trip your breaker besides overheating the existing MMC.

Do you have a JavaTC dump for your coil?  Or a link to parameters from a similar EVR coil?  That would provide estimates of secondary inductance and frequency, coupling factor, etc.
David Knierim

Offline fh89

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Re: Large musical DRSSTC first light!
« Reply #7 on: February 11, 2021, 09:06:52 PM »
Quote
My CM300 coil runs at 38kHz with a 0.6uF MMC (5s20p array of 942C - not recommended if you're starting from scratch, but I already had most of these caps from the previous spark gap model). My CM600 coil will be between 1.25uF and 1.56uF, based on experimentation. For a coil your size, I would expect at least 0.8uF, probably closer to 1uF to be a good value, based on other similar designs. There are a bunch of tradeoffs involved, and I'm curious to see how your testing with long on times works out for spark formation. Just watch your temps

1uF puts me at about 4.5 turns, 1.5uF puts me at about 3.5. Is there some minimum number of primary turns for optimum performance?

Quote
You might want to lower your OCD threshold to a known lower value just to see where your peak is at in case you don't have a means of measuring it in realtime. I don't think the UD+ will freewheel until you hit OCD. As others have said, you'll see more heat dissipation per unit time until you start freewheeling.

I'lll try it with 1000A current limit first and see how it goes. That should put me at 158Arms at 1.12ms at 48Hz 5.4%duty cycle. 

Quote
Is this your first DR coil?
This is actually my second one, but the last one was built way back in 2007! The technology and knowledge has changed quite a bit since then. I've also built 4 or 5 spark gap coils long ago.
 



Quote
Yes, definitely explore behavior of your coil with longer on-times and more measurements using your existing MMC before changing.
Will do some testing next weekend, won't be able to fire the coil up this weekend.

Quote
Measuring primary current during operation would be ideal.  This can be done with an additional CT, or by scoping across the driver's feedback input resistor.  Knowing the operating frequency and current ramp-up and limiting (if any) will help in picking your next MMC capacitance.  If you are hitting 2000A for a reasonable portion of each enable pulse, then I wouldn't increase capacitance.

Is this also true for running in freewheel mode?

I have a current monitor installed on the coil, just haven't had it connected to the scope while the coil was actually running. Is it safe to connect the scope with 12'+ streamers flying around? I think i have a 25' coax to connect it with.



Quote
Does your controller have a single-shot mode?  I think most do.  I'd use that first for long-enable-pulse testing before running at 48Hz.
Unfortunately no single-shot mode on this controller.

Quote
5% duty cycle will likely trip your breaker besides overheating the existing MMC.
I don't doubt this. I will be running on a 100A breaker, so I can turn it up at least a bit.

Quote
Do you have a JavaTC dump for your coil?  Or a link to parameters from a similar EVR coil?  That would provide estimates of secondary inductance and frequency, coupling factor, etc.

I don't but secondary inductance is 265mH. I can run the inputs into JavaTC if you're interested.





« Last Edit: February 11, 2021, 09:08:35 PM by fh89 »

Offline acobaugh

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Re: Large musical DRSSTC first light!
« Reply #8 on: February 11, 2021, 10:28:11 PM »
# of turns might affect your coupling. JavaTC will predict that. But, as @davekni suggested, try to explore the parameter space you have now without changing components. Being able to burst is really helpful when changing parameters. I usually use a super short burst from my interrupter after swapping parts and such to minimize the potential damage if I get something wrong. My interrupter is Gao's MIDI2 controller with a simple 555 circuit switching a BJT in front of the controller's output. Two different ranges, and I can vary the on time and off time separately. If this is just PWM control, then you could breadboard together Steve Ward's 555-based interrupter if you don't/can't modify your existing controller.

Yes, it is safe to use the CT with the coil running. Just make sure the coax is routed so it won't get hit by arcs and/or shield it with some metal screen, conduit, etc. I do this all the time to watch the current envelope with the coil running full power. I actually picked up one of those cheap import battery powered single channel scopes off of Amazon just for this purpose, "just in case." Also, make sure the CT is on one leg of the primary circuit right after the bridge. You don't want your CT between your MMC and your primary, or you'll be stress testing the insulation on your CT.
 

Offline davekni

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Re: Large musical DRSSTC first light!
« Reply #9 on: February 11, 2021, 10:55:54 PM »
Yes, scoping is fine.  Do add a secondary shield of some sort as acobaugh said.  I usually run a strip of grounded aluminum foil or aluminum window screen over scope cables.  Since I'm focused on the electrical/physics side, I scope four channels every time my DRSSTC runs.  Usually that is primary current, secondary current, one H-Bridge output and one gate.  (Gate probing is with a crude home-built fiber-optic-isolated probe.)  Of course, run scope cables the opposite direction as the breakout point.

My quick estimate is 45pF capacitance on your 0.265H secondary for 46kHz unloaded.  That is likely dropping to ~38kHz with arc capacitance, so your primary may be tuned around 38kHz for good performance.

For long on-times, it is generally better to keep primary resonant impedance on the high side.  My guess is that 0.57uF may be about ideal for your build.  Testing will show.

With a 100A breaker, you will probably be fine testing a few seconds at a time at 5% duty cycle.  Worst-case current draw would be just hitting 2000A without much pulse skipping.  That would be 1273A * 5.4% = 68.7A DC from your voltage-doubled bus, so 137.5A average from the line.  Power factor will bring that to 200+A RMS.  But this is worst-case.  And a 100A breaker should allow a couple seconds at 200A.  Reducing OCD setpoint is still a good idea for initial long-enable-pulse testing.

Would love to see some scope captures of this nice coil when you get to testing!
David Knierim

Offline acobaugh

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Re: Large musical DRSSTC first light!
« Reply #10 on: February 12, 2021, 12:48:23 AM »
More importantly, do you have video you can share?

Offline fh89

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Re: Large musical DRSSTC first light!
« Reply #11 on: February 12, 2021, 08:28:22 AM »
Thanks for all the help and valuable feedback guys! I will keep you all updated with results!

Quote
More importantly, do you have video you can share?

Running in manual mode

running in midi mode


Offline Uspring

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Re: Large musical DRSSTC first light!
« Reply #12 on: February 12, 2021, 03:58:08 PM »
Quote
1uF puts me at about 4.5 turns, 1.5uF puts me at about 3.5. Is there some minimum number of primary turns for optimum performance?

The short answer is yes. The long one is:
The optimum primary inductance depends on your bridges capabilities. If you have a high bus voltage and low max currents you need a higher Z (=impedance) primary tank than in the low voltage and high current case. If you use pulse skipping to limit primary current, you can get away with quite a low primary Z. The drawback is, that you are inputting energy only part of the time, so performance will suffer. It is better to choose primary Z in such a way, that you can input max voltage all of the time and also have a current just below your upper limit. This will maximize input power.

When you start a burst, the input energy will first go into the primary tank and then into the secondary. The arc will then draw power from the secondary and limit current in the primary. The secondary power draw depends on the coupling between primary and secondary, so the coupling value k will also have an effect on primary current. An estimate of the best primary Z can be obtained from the bridges voltage and current capabilities and the coupling.

Even for an optimum choice of primary Z, pulse skipping can still be beneficial, since the primary current initially can become too large due to the secondary being out of tune. That is because primary resonance frequency is often chosen somewhat below secondary resonance frequency. The arc lowers secondary resonance frequency, when it becomes big and so pulls the secondary better into tune. Then secondary power draw will increase, limiting primary current and removing the necessity for pulse skips.

To give a recommendation for the primary tank some more data about your coil is needed.

Offline fh89

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Large coil running at 1.12ms on-time
« Reply #13 on: February 20, 2021, 06:52:37 AM »
Here's some video running at 1.12ms PW. PRF 48-156Hz. Primary current limit set at 2kA. Very hot streamers lighting my grass on fire!

Drawing over 150 Amps at 220V from the wall.


At 48Hz duty cycle is 5.39%


At 156Hz duty cycle is 17.53% which is about 592Arms primary current.


Some phone pics:




The ground strikes are nearly continuous at higher frequencies limiting maximum spark length. I think I need to build a platform to raise the coil higher and let the streamers grow.



Offline davekni

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Re: Large coil running at 1.12ms on-time
« Reply #14 on: February 20, 2021, 07:53:42 PM »
Probably depends on coil parameters, but my longest arcs were with a very short breakout on top, extending barely beyond the toroid OD.  I think that electric field from the toroid is helping push the arc up and away.
David Knierim

Offline fh89

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Re: Large musical DRSSTC first light!
« Reply #15 on: February 20, 2021, 08:27:43 PM »
Quote
   Probably depends on coil parameters, but my longest arcs were with a very short breakout on top, extending barely beyond the toroid OD.  I think that electric field from the toroid is helping push the arc up and away.   

I'll give this a shot next time I run it.

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #16 on: February 21, 2021, 04:28:07 AM »
Was your 151A 25kW reading at 17% duty cycle?  If so, I'm calculating about 80% of pulses are being skipped.  Quite high, but not too surprising given the heavy ground strikes.  Once an arc strikes ground it forms a low-impedance "short", limiting the further energy absorbed by the secondary.  Without much secondary load, primary current rises quickly, holding at your 2000A limit.  As you manage to get longer arcs rather than heavy ground strikes, line power at 17% duty cycle will increase as fewer pulses are skipped.

Did your MMC get hot?  Your high air flow may keep it cool enough even at 592A RMS.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #17 on: February 21, 2021, 05:10:54 AM »
Quote
Was your 151A 25kW reading at 17% duty cycle?
Yes, that photo of the power meter is a video still of the peak reading of a short 10 second run with all settings cranked all the way up as in the second scope shot.

Quote
If so, I'm calculating about 80% of pulses are being skipped.  Quite high, but not too surprising given the heavy ground strikes.  Once an arc strikes ground it forms a low-impedance "short", limiting the further energy absorbed by the secondary.  Without much secondary load, primary current rises quickly, holding at your 2000A limit.
Very interesting information, I appreciate you being able to make calculations like that.
It makes sense that so many pulses were skipped- the red LED on the controller signifying OCD was illuminated then entire video (you can see it on in the right side of the photo)

I may try to modify the controller for a higher current limit (I've seen people run 4kA on cm600's) but first I will experiment with longer on-times, raising the coil and the shorter break out point. I also have 10000uF worth of caps on the way to add to the bus.

Quote
As you manage to get longer arcs rather than heavy ground strikes, line power at 17% duty cycle will increase as fewer pulses are skipped.
Wow, already at 150A, wonder how high I can go for short runs before tripping the breaker? May have to look into getting a 200A breaker.

Quote
Did your MMC get hot?  Your high air flow may keep it cool enough even at 592A RMS.

All I can say for sure is that it was cool to the touch 30 seconds after a run. I wasn't brave (or foolish? I don't have any bleeders on the MMC) enough to stick my hand in there sooner. The primary was warm but not hot. Secondary was cool.
I don't currently have a way to actually measure the temp of the MMC or IGBTs, but I will pick up an IR thermometer and see if I can get a reading. I kept all runs <1 min and waited at least 2-3 minutes between runs.

« Last Edit: February 21, 2021, 05:14:52 AM by fh89 »

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #18 on: February 21, 2021, 06:50:03 AM »
BTW, 75% power factor is higher than I would have guessed.  For my curiosity, I made an LTSpice simulation of just line impedance and voltage doubler.  Adjusted parameters to get a fit with your meter readings based on unloaded line voltage being 240V RMS.  Setting total line resistance to 0.175 ohms and line inductance to 60uH made numbers match well.  These numbers seem reasonable since line impedance includes your power cord all the way back to winding resistance and leakage inductance of the transformer feeding your breaker box.

If this is accurate, power line resistance and inductance is providing enough filtering to keep power factor reasonably high.  That keeps power factor from being sensitive to bulk capacitance.  I was originally going to reply with a concern that increasing bus capacitance would reduce power factor.  In my simulation, adding 10mF (20mF per half of the doubler) made an insignificant reduction in power factor.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #19 on: February 21, 2021, 07:33:42 AM »
Quote
BTW, 75% power factor is higher than I would have guessed.  For my curiosity, I made an LTSpice simulation of just line impedance and voltage doubler.  Adjusted parameters to get a fit with your meter readings based on unloaded line voltage being 240V RMS.  Setting total line resistance to 0.175 ohms and line inductance to 60uH made numbers match well.  These numbers seem reasonable since line impedance includes your power cord all the way back to winding resistance and leakage inductance of the transformer feeding your breaker box.

If this is accurate, power line resistance and inductance is providing enough filtering to keep power factor reasonably high.  That keeps power factor from being sensitive to bulk capacitance.  I was originally going to reply with a concern that increasing bus capacitance would reduce power factor.  In my simulation, adding 10mF (20mF per half of the doubler) made an insignificant reduction in power factor.

Once again, I appreciate the analysis. I briefly looked into adding active PFC, but quickly gave up on the idea after realizing the cost and complexity of a boost converter with the necessary ratings. Good to know the extra capacitance shouldn't hurt PF too much.

I went ahead and uploaded the power meter video because I thought you might find it interesting. The PF drifts around a bit of course, but it seems to stay over 70% while the coil is running.


Offline Mads Barnkob

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Re: Large coil experimenting with long on-times.
« Reply #20 on: February 21, 2021, 12:24:41 PM »
Such an awesome coil!, that is quite amazing that you can run it at such long on-times. I am wondering if it really is needed to grow long sparks, your longer on-time just makes them more fat?

High impedance coils usually also like long on-time, so if you experiment with 1uF+ MMC, you are getting into the territory of Kizmox / Dalus like coils, which operate with very low impedance, high peak currents and short on-times.

Regarding the power meter and its measurements. The PF does seem high. It "should" be 0.5-0.6 without any kind of PFC. With a variac in front it could climb to 0.7'ish from the added inductance. Maybe I am just used to being too close to a transformer station... The mains destribution network in Denmark relies on much bigger transformers, we do not have polepigs. Could it be that the power meter is not suitable for high frequency current peaks?

When I built my PM700 power meter box, I made sure to find a meter and current transformers that was good up to 10 kHz harmonics.
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #21 on: February 21, 2021, 07:18:52 PM »
Quote
Such an awesome coil!, that is quite amazing that you can run it at such long on-times. I am wondering if it really is needed to grow long sparks, your longer on-time just makes them more fat?
Thanks, I appreciate it! I'm not sure how much longer the sparks are with the longer on-times because they seem to be going straight down for the most part. As I mentioned in an earlier post, I have a few things to try to fix this.

I also have another interrupter in the works that will be able to run much longer on-times, and I'll see if I can get some extra spark length out of longer pulses at lower PRFs.

Quote
High impedance coils usually also like long on-time, so if you experiment with 1uF+ MMC, you are getting into the territory of Kizmox / Dalus like coils, which operate with very low impedance, high peak currents and short on-times.

Wait, I'm confused here- so if I want to design an MMC optimized for long on-times, I want a larger capacitance value?

Quote
Regarding the power meter and its measurements. The PF does seem high. It "should" be 0.5-0.6 without any kind of PFC. With a variac in front it could climb to 0.7'ish from the added inductance. Maybe I am just used to being too close to a transformer station... The mains destribution network in Denmark relies on much bigger transformers, we do not have polepigs.

Hmm. There is only maybe 150' of wire total between my coil and the distribution xfrmr, you can see it right behind my yard in this pic:
 [ You are not allowed to view attachments ]

I have no idea how to calculate how much inductance this adds to the circuit.

Quote
Could it be that the power meter is not suitable for high frequency current peaks?

This very well could be true, it was a vey inexpensive ebay meter- like $25 USD. I was unaware that the PF reading could be inaccurate with HF current peaks.

Quote
When I built my PM700 power meter box, I made sure to find a meter and current transformers that was good up to 10 kHz harmonics.
That is a much more sophisticated device, I have no doubt it gives more accurate PF reading.


**side note** [ You are not allowed to view attachments ]  Why does this keep happening? It seems to work sometimes and not others.
« Last Edit: February 21, 2021, 07:22:21 PM by fh89 »

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #22 on: February 21, 2021, 10:19:33 PM »
Agreed that 75% PF sounds high, but I think it is likely real.  Line resistance is the key contributor here.  Notice that RMS voltage drops from 241V at low load to 220V at high load.  That fits my spice simulation with 0.17ohms.  With just that resistance, power factor is 72.7%.  With 100uH added, power factor is 75% as measured.  (I've updated simulation parameters a bit based on the most recent video with more meter data.)  Both 0.17ohms and 100uH seem plausible for the pictured power connection.

At light load, power factor is lower as would be expected.  Power factor matters only at high load, since that is what limits total power obtainable from a given circuit.  Series resistance can increase total available power even though it is wasting power.  That is because (up to a point) resistance reduces RMS current more than it reduces RMS voltage.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #23 on: February 22, 2021, 06:32:34 AM »
**Update** Longer sparks and explosions?

Raised toroid, used shorter breakout point, and adjusted tuning resulting in improved performance and dramatic explosions!

This ground strike is 14' linear from breakout point to ladder.



Explosion!



This was one of the steel fasteners becoming superheated and melting/exploding from the high current. No damage to the coil/electronics.



There was one other fastener with some melting:



I can't wrap my head around why this one fastener in particular took the brunt of the heating and all the rest were fine. All of these fasteners were very tight, and the current path was not directly through this area. The arc hit the strike rail on the left side of the below photo. The melted fastener is the near corner. The strike ring is grounded to the frame on the right side primary stand-off, behind the near corner. The frame is connected to RF ground in the rear of this photo.



I would expect the current path to be like this:



Here's video of the exploding fastener:


It's really interesting that after the initial strike rail hit and subsequent shutdown of the coil, the fastener remained hot enough to instantly melt/explode again through inductive heating alone
upon firing the coil back up.


Here's some video of the improved spark length. The shorter breakout point does seem to help push the sparks out instead of down. Still think the coil could perform better higher off the ground. The interesting thing is that I had to change the tuning to get maximum spark length at this higher pulse width. Does this make sense? Is it expected to require a different tap point with longer on-times? Maximum spark length at 360us was 6.25 turns; tap point for 1.12ms performed best at 7.5 turns (the full primary on this coil, maybe it would be even better with more turns?)


In this video, I turn down the PRF and the output becomes very sputtery for lack of a better word, almost like it's out of tune. I then turn down the PW and the output almost disappears even at like 300us, like it's way out of tune
« Last Edit: September 11, 2021, 09:09:18 AM by fh89 »

Offline Hydron

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Re: Large coil experimenting with long on-times.
« Reply #24 on: February 22, 2021, 11:19:03 AM »
Wow, great videos and the fireworks from the bolt are pretty spectacular given that nothing important went pop.

In the second video I see what looks to be an arc from something internal (not the bolt that sparked earlier in the clip) - do you know what that was?

Finally tuning the primary lower for longer on-time makes perfect sense - as the arc grows with on-time it de-tunes the secondary, pulling it's resonant frequency lower. When the primary is tuned lower this improves the match and energy transfer between the two.
With lower PRF you're putting less power into the arc, therefore it isn't as long and the secondary resonance frequency remains higher. I have especially noticed this back when I had my bigger coil tuned for low-Z bus operation with high primary detuning - streamer length was pretty poor until you got the power to a certain level (via increasing bus voltage/pulsewidth/PRF), and then it really took off as the detuning came into play. Gave impressive and chaotic streamers, but wasn't so good for MIDI mode, where you want the streamer growth to be more linear with increasing pulsewidth/PRF.

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Re: Large coil experimenting with long on-times.
« Reply #25 on: February 22, 2021, 12:21:15 PM »
What a great capture of that failure! When people ask for advise, the one I give the first is to always have a camera rolling!

I think I know what happens before and during the continues "explosion".

The aluminium profiles are most likely anodized and that is actually an electrical insulation. So your high voltage arc knocks through the anodized layers and forms a nice current path for the upper part of the frame, it is now seen by the primary coil as a single turn winding underneath it and it starts to pull some serious power and thus is why you see steel bolts melting instantly.

The flashover between bolts and plate would be in the place with the worst connection, just like a bad connection on a mains feeder will heat up from the increased resistance, its just the point of failure and it has really nothing to do with the sparks anymore, it was just the initiator of the underlying problem (single turn metal construction too near the primary coil)
« Last Edit: February 22, 2021, 12:23:46 PM by Mads Barnkob »
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Offline Hydron

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Re: Large coil experimenting with long on-times.
« Reply #26 on: February 22, 2021, 02:56:02 PM »
Makes me thing about what could be done deliberately to add some hot metal & sparks to the show of a high power DRSSTC... maybe a single turn coil with a high-resistance part designed to emit the fireworks. Would need to be careful about where said hot metal flies though.

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #27 on: February 22, 2021, 05:58:01 PM »
Quote
In the second video I see what looks to be an arc from something internal (not the bolt that sparked earlier in the clip) - do you know what that was?
It was from somewhere in this area. There is some carbon tracking on the primary lead coming from the MMC. I think it was probably from there to the current transformer that was left floating.



Quote
Finally tuning the primary lower for longer on-time makes perfect sense - as the arc grows with on-time it de-tunes the secondary, pulling it's resonant frequency lower. When the primary is tuned lower this improves the match and energy transfer between the two.
With lower PRF you're putting less power into the arc, therefore it isn't as long and the secondary resonance frequency remains higher.

This is extremely interesting. I wouldn't have expected this effect to be so dramatic. I may have to rebuild my primary with more turns to run longer on-times!


Quote
What a great capture of that failure! When people ask for advise, the one I give the first is to always have a camera rolling!
Thanks, good advice!

Quote
I think I know what happens before and during the continues "explosion".

The aluminium profiles are most likely anodized and that is actually an electrical insulation. So your high voltage arc knocks through the anodized layers and forms a nice current path for the upper part of the frame, it is now seen by the primary coil as a single turn winding underneath it and it starts to pull some serious power and thus is why you see steel bolts melting instantly.

The flashover between bolts and plate would be in the place with the worst connection, just like a bad connection on a mains feeder will heat up from the increased resistance, its just the point of failure and it has really nothing to do with the sparks anymore, it was just the initiator of the underlying problem (single turn metal construction too near the primary coil)

This makes sense and is a good explanation. Still surprising to me- I thought I would be ok because of aluminum being non-ferrous, the entire frame is located outside of the outer turn of the primary, and the distance the primary is from the frame.

You can see in this photo the corner with the melted bolt is well outside the primary, and you can also see the primary standoffs are all outside the outer edge of the primary.


The primary is also 8" above the frame:


Obviously none of this matters as much as I thought it would! I guess I need to try to figure out how to put a gap in the upper frame rail without compromising the structural integrity of the frame because this thing is really heavy! Any idea how much of a gap would be sufficient to remedy the shorted turn effect? Would 1 inch work?


« Last Edit: February 22, 2021, 06:06:48 PM by fh89 »

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #28 on: February 22, 2021, 06:38:04 PM »
I'd say that Mads and Hydron "hit the nail on the head", except that you are using screws :)

Could you make some of the triangular corner-connector pieces out of polycarbonate or fiberglass?

Besides avoiding the shorted turn at the top, you still want a ground path for all metal frame parts.  My thought is to make each top edge extrusion connect at one end to the vertical post going down, but not connect at the other end (via plastic connector pieces).

Yes, you have large spacing, but your coil is large and high-power.  Relative spacing is what matters.

For detuning, consider the arc length compared to top-load dimensions.  The arc is much longer, making total capacitance much larger.  The advantage of skip-pulse is allowing long runs at max current - long enough until an arc manages to pull the secondary frequency down to match primary.  My arc length is limited because if I detune any further I hit OCD before enough arc forms to bring it back in tune.

Concerning intentional metal sparks for Tesla coil shows, I suggest using sparking metal as the breakout.  I do this on my SSTC, both with fine metal springs and with aluminum window screen.  (It is only 3kW, so barely enough to spark the breakout.  Your coil should be impressive with such breakout points.)

It looks like you have enough yard space to move the breakout point even farther onto the top of the coil.  That may help even more to direct arcs away from ground.  (I couldn't go farther onto the top without arcs going back to my roof.)
David Knierim

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Re: Large coil experimenting with long on-times.
« Reply #29 on: February 22, 2021, 07:47:07 PM »
Quote
In the second video I see what looks to be an arc from something internal (not the bolt that sparked earlier in the clip) - do you know what that was?
It was from somewhere in this area. There is some carbon tracking on the primary lead coming from the MMC. I think it was probably from there to the current transformer that was left floating.


You should move your CT. The primary circuit voltage is at its highest just at that point between the L and C of the primary resonant circuit. Please the CT at either output leg of the inverter, but never between the primary coil and MMC.

Your CT has properly only survived because of its internal resistor for 50 Ohm output impedance. A open loop CT secondary side can produce very high voltages and fail from it. https://voltage-disturbance.com/power-engineering/open-circuit-current-transformer-characteristics/


Quote
I think I know what happens before and during the continues "explosion".

The aluminium profiles are most likely anodized and that is actually an electrical insulation. So your high voltage arc knocks through the anodized layers and forms a nice current path for the upper part of the frame, it is now seen by the primary coil as a single turn winding underneath it and it starts to pull some serious power and thus is why you see steel bolts melting instantly.

The flashover between bolts and plate would be in the place with the worst connection, just like a bad connection on a mains feeder will heat up from the increased resistance, its just the point of failure and it has really nothing to do with the sparks anymore, it was just the initiator of the underlying problem (single turn metal construction too near the primary coil)

This makes sense and is a good explanation. Still surprising to me- I thought I would be ok because of aluminum being non-ferrous, the entire frame is located outside of the outer turn of the primary, and the distance the primary is from the frame.

You can see in this photo the corner with the melted bolt is well outside the primary, and you can also see the primary standoffs are all outside the outer edge of the primary.


The primary is also 8" above the frame:


Obviously none of this matters as much as I thought it would! I guess I need to try to figure out how to put a gap in the upper frame rail without compromising the structural integrity of the frame because this thing is really heavy! Any idea how much of a gap would be sufficient to remedy the shorted turn effect? Would 1 inch work?
[/quote]
1 inch would be fine, it is only the induced magnetic field you are fighting here, not a high voltage. Even less could properly do it too.

Just for the fun of it, I simulated your primary coil + MMC with a 1 turn secondary coil underneath it, 8" like your frame and the coupling is actually higher than I expected.



**side note** [ You are not allowed to view attachments ]  Why does this keep happening? It seems to work sometimes and not others.

I think there is some issues between attachment plugin and preview function, did you use preview?
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Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #30 on: February 22, 2021, 08:42:57 PM »
Using Mads JavaTC numbers, I'm calculating 600V peak around your rail at 2000A primary.  Rail inductance is reported to only one digit (2uH), so my calculation is correspondingly imprecise.  Still, a 2mm gap should be plenty.

Of the primary magnetic flux passing through the that top square rail, 1/4th of it passes through each side, for 150V peak.  That is why I suggested breaking the top rail connections at each corner, not just once in the loop.  A path to ground is necessary to handle strikes from the secondary.  So each edge of the top square can connect to one vertical post (but not the other) to provide that path.  It would be best for the intended connection paths to be robust.  I'd suggest sanding/grinding through the thin anodization layer where electrical connections are intentional, and using plastic where connections are to be avoided.
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #31 on: February 22, 2021, 09:08:44 PM »
Quote
Could you make some of the triangular corner-connector pieces out of polycarbonate or fiberglass?

Besides avoiding the shorted turn at the top, you still want a ground path for all metal frame parts.  My thought is to make each top edge extrusion connect at one end to the vertical post going down, but not connect at the other end (via plastic connector pieces).

I have some leftover 1/4" G10 that I can make a sturdy brackets out of. Right now, the vertical pieces and edge pieces all butt up against each other. I could make a top bracket out of the G10 and cut one of the edge pieces 1/4" short to make a gap. This will unshort the turn and hopefully still maintain a very rigid and strong frame.

Quote
Concerning intentional metal sparks for Tesla coil shows, I suggest using sparking metal as the breakout.  I do this on my SSTC, both with fine metal springs and with aluminum window screen.  (It is only 3kW, so barely enough to spark the breakout.  Your coil should be impressive with such breakout points.)

Would be cool to vaporize some metal (intentionally this time.) Pretty sure I have some screen laying around somewhere.

Quote
It looks like you have enough yard space to move the breakout point even farther onto the top of the coil.  That may help even more to direct arcs away from ground.  (I couldn't go farther onto the top without arcs going back to my roof.)
I'll give this a shot.

Quote
You should move your CT. The primary circuit voltage is at its highest just at that point between the L and C of the primary resonant circuit. Please the CT at either output leg of the inverter, but never between the primary coil and MMC.
I think Dave mentioned this also in a previous post. I'll get it moved before the next run.

Quote
1 inch would be fine, it is only the induced magnetic field you are fighting here, not a high voltage. Even less could properly do it too.
I'll try Dave's idea of replacing one of the corner brackets and I'll introduce a small gap. Hopefully it will be enough.

Quote
Just for the fun of it, I simulated your primary coil + MMC with a 1 turn secondary coil underneath it, 8" like your frame and the coupling is actually higher than I expected.
That's interesting! Clearly quite a bit of power is being transferred to the frame. Hopefully the corner mods will help!

Quote
I think there is some issues between attachment plugin and preview function, did you use preview?
I've tried it both ways- Previewing first, and posting without previewing first. Doesn't seem to matter.


Quote
Of the primary magnetic flux passing through the that top square rail, 1/4th of it passes through each side, for 150V peak.  That is why I suggested breaking the top rail connections at each corner, not just once in the loop.  A path to ground is necessary to handle strikes from the secondary.  So each edge of the top square can connect to one vertical post (but not the other) to provide that path.  It would be best for the intended connection paths to be robust.  I'd suggest sanding/grinding through the thin anodization layer where electrical connections are intentional, and using plastic where connections are to be avoided.

That would be ideal, but it is much more work- I would need to replace all 4 top corner brackets and cut each of the 4 edge pieces. I'm hoping replacing a single bracket and using a larger gap will be good enough. If I continue to have issues, this will be the way I go.

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Re: Large coil experimenting with long on-times.
« Reply #32 on: February 22, 2021, 10:19:48 PM »
If you were to make 4 gaps, it's only 150V per gap.  A plastic shim would be sufficient insulation - something like 4 or 5-mil mylar transparency film.  That way perhaps you could avoid cutting any of the extrusions.  For that matter, 4-mil mylar would be fine at 600V.  Success of a single break will depend on which other joints happen to conduct or not (ie. on what bits of anodization have been scraped through or not during construction). 

All joints solidly conducting is an option too.  A solidly-conducting shorted loop would reduce primary inductance, so require a bit of retuning.  If conducting, that upper frame ring would conduct about 1.1kA peak.  A solid connection for that current would require non-anodized parts well clamped together.  Breaking connections is probably easier than making connections good for 1.1kA peak.
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #33 on: February 22, 2021, 10:43:49 PM »
If you were to make 4 gaps, it's only 150V per gap.  A plastic shim would be sufficient insulation - something like 4 or 5-mil mylar transparency film.  That way perhaps you could avoid cutting any of the extrusions.  For that matter, 4-mil mylar would be fine at 600V.  Success of a single break will depend on which other joints happen to conduct or not (ie. on what bits of anodization have been scraped through or not during construction). 

All joints solidly conducting is an option too.  A solidly-conducting shorted loop would reduce primary inductance, so require a bit of retuning.  If conducting, that upper frame ring would conduct about 1.1kA peak.  A solid connection for that current would require non-anodized parts well clamped together.  Breaking connections is probably easier than making connections good for 1.1kA peak.

Insulating the edge pieces from the verticals would be easy enough with this method, but the top corner brackets would still be shorting everything together. They would be much harder to insulate. I guess I could drill out the bolt holes and press in nylon sleeves, then use nylon washers on the bolts.

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Re: Large coil experimenting with long on-times.
« Reply #34 on: February 22, 2021, 11:40:29 PM »
Yes, I was thinking of your G10 for corner pieces.  Isolated connections using metal pieces is complex (ie. nylon sleeves and washers as you suggest).  Not that I know what I'm talking about when it comes to mechanical construction.  My DRSSTC base is a stack of plastic milk crates.  Hardest part was cutting out the steel reinforcement rib at the top without damaging the plastic.  Had to remove the steel rib for the same reason - it formed a shorted turn.
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #35 on: February 23, 2021, 04:42:02 AM »
Yes, I was thinking of your G10 for corner pieces.  Isolated connections using metal pieces is complex (ie. nylon sleeves and washers as you suggest).  Not that I know what I'm talking about when it comes to mechanical construction.  My DRSSTC base is a stack of plastic milk crates.  Hardest part was cutting out the steel reinforcement rib at the top without damaging the plastic.  Had to remove the steel rib for the same reason - it formed a shorted turn.

Well I was all ready to start cutting G10, ordered some mylar sheets off Amazon, popped off a corner to use as a stencil, and instantly had a DOH! moment.


Of course the side corner pieces sort the rails together also! No way I'm going to make 12 G10 corner pieces! I think my best bet at this point is to cut a small gap in the rear rail, then reinforce on 3 sides with strips of the G10.

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Re: Large coil experimenting with long on-times.
« Reply #36 on: February 23, 2021, 06:06:27 AM »
It would be only 8 corner pieces, not all 12.  You want a ground path for each of the four horizontal extrusion pieces.  I had no idea how hard or easy it would be to make eight G10 corner pieces.

I'd still consider making two G10 corner pieces and isolating an existing corner rather than cutting in the middle of an extrusion.  That way if you avoid a patch in the middle of your clean build.  Also, if you find that more breaks are needed, you are already 1/4th of the way there.

Is there enough clearance in the existing corner piece holes that you could add a small section of heat-shrink around the head-end of the screws and still fit?  That and nylon washers and mylar (or kapton tape) around one end of each horizontal extrusion would work.  That's a total of 16 nylon washers, as only the four screws at one end of each extrusion need insulating.

BTW, I found a scrap of what looks like the same extrusion as you are using.  The scrap I have is definitely anodized.

Of course, this is your build, so modify as you see fit!  Good luck with the upgrade!
« Last Edit: February 23, 2021, 06:15:30 AM by davekni »
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #37 on: February 23, 2021, 07:27:25 AM »
Quote
Is there enough clearance in the existing corner piece holes that you could add a small section of heat-shrink around the head-end of the screws and still fit?  That and nylon washers and mylar (or kapton tape) around one end of each horizontal extrusion would work.  That's a total of 16 nylon washers, as only the four screws at one end of each extrusion need insulating.

I think I'll go with this idea. McMaster Carr has nylon sleeve washers https://www.mcmaster.com/91145A165/ that would be perfect for this. Washer and insulating sleeve in one. Drilling out the holes in the brackets to press-fit the sleeve washers will be way easier than making the G10 corner brackets. The Kapton tape is a good idea too. I appreciate the feedback! Maybe you are better at structural engineering than you give yourself credit for!

Quote
BTW, I found a scrap of what looks like the same extrusion as you are using.  The scrap I have is definitely anodized.
It's 80/20 brand T-slot aluminum. Definitely anodized, sorry for not acknowledging that before, I took it as an observation.

 
Quote
Of course, this is your build, so modify as you see fit!  Good luck with the upgrade!
Thanks!
« Last Edit: February 23, 2021, 08:11:41 AM by fh89 »

Offline Mads Barnkob

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Re: Large coil experimenting with long on-times.
« Reply #38 on: February 23, 2021, 11:20:12 AM »
How about replacing one of the horizontal extrusions with something made out of non-conductive material, then you do not need to redo any corners.

You could also just cut out a 1" piece of a horizontal extrusion, as you suggested earlier and replace the missing piece with a machined counterpart of G10 knocked into each extrusion to give it some sturdiness or even mount some more pieces on the outside using just regular screws/nuts in the extrusion slots.

You should also use a dedicated conductor from strike rail to RF ground, do not lead that through the anodized frame.
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Offline Hydron

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Re: Large coil experimenting with long on-times.
« Reply #39 on: February 23, 2021, 04:39:06 PM »
Isolating both top rails at 2 opposing corners would be best (should eliminate the whole shorted turn path), though 1 should be a lot better than nothing (would leave half of the path there next to the primary and the other half via the bottom rails). Looks to me like some thin shims and isolating the screws from the triangular aluminium bits would do the job. If you're feeling lazy you could order some 0.8mm PCBs (without copper) with the correct shape and hole spacing (0.8mm was the same price as 1.6mm last time I ordered a thin PCB, going below this got pricey).

As for the CT on the primary, looks like the rating is 700A RMS (and it is internally terminated) so you're probably safe there to leave it connected unless you start pushing a few 10s of % duty cycle, but as Mads said, put it between the bridge and one of the primary tank components (capacitor or primary coil), not between the cap and primary. It's likely possible to insulate it from the primary voltage seen in the current location, but is unnecessary effort vs just putting it somewhere safer.

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #40 on: February 23, 2021, 05:59:53 PM »
Quote
How about replacing one of the horizontal extrusions with something made out of non-conductive material, then you do not need to redo any corners.
This would work if I could find a suitable replacement material in the same t-slot design. The problem for me here is the strength needed. One of the great things about the 80/20 framing system is that the joints are rock solid and very strong. My secondary coil assembly weighs 77 lbs and the toroid is 29lbs, so it is supporting 106 lbs (48kg). I am able (with a helper) to lift the entire coil by the side handles without worry of something breaking in the frame.

Quote
You could also just cut out a 1" piece of a horizontal extrusion, as you suggested earlier and replace the missing piece with a machined counterpart of G10 knocked into each extrusion to give it some sturdiness or even mount some more pieces on the outside using just regular screws/nuts in the extrusion slots.
This is exactly what I was thinking until Davekni made some great alternative suggestions. I think isolating one end of each corner will get the job done without compromising the structural integrity of the frame.

Quote
You should also use a dedicated conductor from strike rail to RF ground, do not lead that through the anodized frame.
Terrific suggestion, I will make this change! Seems stupid in hindsight that I connected it this way to start!


Quote
Isolating both top rails at 2 opposing corners would be best (should eliminate the whole shorted turn path), though 1 should be a lot better than nothing (would leave half of the path there next to the primary and the other half via the bottom rails). Looks to me like some thin shims and isolating the screws from the triangular aluminium bits would do the job. If you're feeling lazy you could order some 0.8mm PCBs (without copper) with the correct shape and hole spacing (0.8mm was the same price as 1.6mm last time I ordered a thin PCB, going below this got pricey).
This is the way I'm going to go basically, but I'll go ahead and isolate one end of each of the four top rails.

Quote
As for the CT on the primary, looks like the rating is 700A RMS (and it is internally terminated) so you're probably safe there to leave it connected unless you start pushing a few 10s of % duty cycle, but as Mads said, put it between the bridge and one of the primary tank components (capacitor or primary coil), not between the cap and primary. It's likely possible to insulate it from the primary voltage seen in the current location, but is unnecessary effort vs just putting it somewhere safer.
I already removed it. There is no convenient place to mount it next to the inverter outputs so I'm just going to leave it out for now. I really only needed it to check the phase-lead was correct.




Offline Hydron

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Re: Large coil experimenting with long on-times.
« Reply #41 on: February 23, 2021, 07:58:33 PM »
Thinking about my previous suggestion, you could also just get the triangle bits made out of PCBs, that way no insulators are required for the bolts, just a little insulating shim at the end where the rail butts up against the upright. You'd want them thick rather than thin in this case, but stacking 2 or 3 could be an option given how cheap they are (also available in different colours!). Again would only need 2 corners to be fully insulated, or 4 with one rail insulated.

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #42 on: February 23, 2021, 08:07:41 PM »
Hydron's version of fully-insulating two opposing corners saves a bit of work over my suggested version.  Only 6 corner pieces need modifying for shoulder washers rather than 8.  It functions the same electrically - one end of each 80/20 extrusion is insulated and another end is grounded to a vertical strut.  Only reason to do my version is if you like the symmetry of all four corners being identical.
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Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #43 on: February 24, 2021, 12:36:24 AM »
Quote
Thinking about my previous suggestion, you could also just get the triangle bits made out of PCBs, that way no insulators are required for the bolts, just a little insulating shim at the end where the rail butts up against the upright. You'd want them thick rather than thin in this case, but stacking 2 or 3 could be an option given how cheap they are (also available in different colours!).
Ordered the nylon sleeve washers already, should be here tomorrow. I think the insulator method will allow me to maintain the high level of strength and clean look of the current frame.
Quote
Again would only need 2 corners to be fully insulated, or 4 with one rail insulated.
Good point, I can save a bit of work this way.

Quote
Hydron's version of fully-insulating two opposing corners saves a bit of work over my suggested version.  Only 6 corner pieces need modifying for shoulder washers rather than 8.  It functions the same electrically - one end of each 80/20 extrusion is insulated and another end is grounded to a vertical strut.  Only reason to do my version is if you like the symmetry of all four corners being identical.
This is a good idea, I'll go ahead and do both rails on two opposing corners. Thanks for the suggestions guys!

Offline acobaugh

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Re: Large coil experimenting with long on-times.
« Reply #44 on: February 24, 2021, 01:17:22 AM »
On the rail heating topic - since you want to get the thing up off the ground, why not take this opportunity to do just that? Use some sort of insulating material to replace the aluminum posts that hold up the primary, and double the distance from the primary to the top of the base? Just a thought.  Good to see we're learning where the limitations are. I bet it's even more impressive in person with those super fat arcs.

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #45 on: February 24, 2021, 06:55:15 AM »
Quote
On the rail heating topic - since you want to get the thing up off the ground, why not take this opportunity to do just that? Use some sort of insulating material to replace the aluminum posts that hold up the primary, and double the distance from the primary to the top of the base? Just a thought.
This is a possibility, but I would need to order more 80/20 rail, and extend the coolant lines. I wouldn't use anything other than the extruded aluminum rails for the primary supports as the secondary and toroid assembly weigh over 100 pounds requiring very strong supports. Even then, I'm not sure I could go double without making it too top-heavy and unstable. I built a 2' tall stand as a temporary measure that I will try out next time.

Quote
Good to see we're learning where the limitations are. I bet it's even more impressive in person with those super fat arcs.
Absolutely! Almost terrifying close-up, I definitely get an adrenaline rush from it. The scale and magnitude really don't translate well on the gopro footage I posted. Here's a video from my buddy's phone that I think gives a little better impression of the scale even though the autofocus is having a hard time with the streamers. I think 14' to the ladder looks more plausible here (it was measured with a tape measure). For some reason the gopro video looks more compressed horizontally. I'm going to try to get some higher quality video made in the future.

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #46 on: February 25, 2021, 06:01:13 PM »
I finished the two corner insulation last night.

Holes in brackets drilled out to fit nylon sleeve washers.


Trimmed flush


Sleeve washers for one corner installed


Kapton tape insulation on underside


Cut some  shims out of HDPE to insulate the rails from the verticals



Added a layer of the kapton tape to the rails


Corner with Kapton tape and HDPE shims


Completed corner


Did the same thing with the opposing corner. Hopefully this will be enough to eliminate the shorted turn effect and stop melting my bolts!

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #47 on: February 25, 2021, 06:49:00 PM »
That looks great for insulation!

You'll still need to make sure the other corners are uninsulated all the way to ground.  Otherwise any secondary strike to to the rails will force its way to ground through some insulated path.  That path might or might not be through your newly-insulated corners.  (The only other option that comes to mind is to add strike rings around the outside to block all arcs from the rails.  I think grounded rails are preferable.)

One option for making corners grounded is to grind away the thin anodization layers (on both extrusions and corner pieces if they are anodized).  Another is to use the cut ends that aren't anodized - connect them with foil or wire or ...  Or drill small holes for small metal (not blued) screws, with wires under the screw heads between extrusion pieces.  This could be on the inside to be less visible.  No matter what technique you pick, I suggest a final continuity check between each frame piece and ground.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #48 on: February 25, 2021, 08:29:10 PM »
I think what I'm going to do is use stainless steel self-tapping screws to bond each corner plate to each rail (aside from the insulated ends of course.) I think this will be the easiest way to get a solid electrical connection without having to take everything apart and grind off the anodization.

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #49 on: February 25, 2021, 08:37:26 PM »
Yes, that sounds easier than my ideas.  Of course, the holes in the corner plates need to be small enough that threads tap into them as well as the 20/80 extrusions.  I presume you are doing this through the lower part of the frame too - all the way until there is some solid connection to ground.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #50 on: February 25, 2021, 09:09:45 PM »
Slight clarification- I'm using self-drilling screws. They drill their own pilot hole a bit smaller than the thread size, so it will automatically be threaded in to both pieces. I will make sure to get every piece a path to ground.

Offline davekni

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Re: Large coil experimenting with long on-times.
« Reply #51 on: February 25, 2021, 11:26:16 PM »
Wow, I didn't realize there were self-drilling screws for more than sheet-metal and wood.  Sounds like an easy fix if they work on your aluminum plates and extrusions.
David Knierim

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #52 on: February 26, 2021, 12:18:08 AM »
Oh, they're intended for sheet metal, but I'm hoping they will work in the soft aluminum! Worst case I can drill pilot holes.

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #53 on: February 26, 2021, 07:20:13 AM »
I added 10,000uF to the bus bringing the total to 16,800uF in preparation for running longer on-times. I have parts for a new interrupter capable of 15ms on-times arriving this weekend.

4 Epcos 10,000uF 350V caps


As close to the bridge as I could get and still have a solid mounting point



Caps bolted to 1/4" polycarbonate front panel.




« Last Edit: February 26, 2021, 09:03:11 PM by fh89 »

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #54 on: March 04, 2021, 07:16:23 AM »
Assembled a new controller from Phillip Slawinski customized for up to 15ms on-times. Duty cycle limit set to 15%.








1.46ms at 100hz max frequency


5ms at 30Hz


15ms at 10HZ


Not sure If I'll get a chance to run the coil this weekend, but I will post results from these on-times if I do!
« Last Edit: March 04, 2021, 07:20:16 AM by fh89 »

Offline fh89

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Re: Large coil experimenting with long on-times.
« Reply #55 on: March 06, 2021, 05:08:48 AM »
Whelp, destroyed the coil running at 4ms tonight, but not the way I was expecting. I thought the MMC would be the first to go, but the secondary coil flashed over and is totally destroyed. :'(



Here's a successful run at 3ms:
/>

And here's the video of the failure:
/>

Not looking too good here folks


Heavy carbon tracking at the bottom of the secondary


Bottom of secondary:


PTFE wrap on the lower end of the secondary was designed to prevent/reduce primary-to-secondary flashover. Not sure that's what happened here, or if it was just secondary flashover due to overcoupling.



Secondary completely destroyed.



My guess is this was caused by the coupling being too high for the very long on-time and power level. JAVATC puts k at .18
Any suggestions for a better k when I make the new secondary? The current secondary winding starts at the height of the primary. If I start it 3 inches higher, the k drops to .119, does that sound better?

Here's the JAVATC dump:

Code: [Select]
J A V A T C version 13.6 - CONSOLIDATED OUTPUT
3/5/2021, 7:48:18 PM

Units = Inches
Ambient Temp = 68ºF

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
6.375 = Radius 1
6.375 = Radius 2
0 = Height 1
46 = Height 2
1703.7 = Turns
23 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
7.5 = Radius 1
13 = Radius 2
0 = Height 1
0 = Height 2
7.5 = Turns
0.375 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.57 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
50.69 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
46 [inch] = Length of Winding
37 [inch] = Turns Per Unit
0.00443 [inch] = Space Between Turns (edge to edge)
5686.9 [ft] = Length of Wire
3.61 [:1] = H/D Aspect Ratio
114.8175 [Ohms] = DC Resistance
72877 [Ohms] = Reactance at Resonance
8.77 [ lbs] = Weight of Wire
228.818 [mH] = Les-Effective Series Inductance
javascript:PopupCenter('out3.html','out3','900','300')237.254 [mH] = Lee-Equivalent Energy Inductance
230.116 [mH] = Ldc-Low Frequency Inductance
43.083 [pF] = Ces-Effective Shunt Capacitance
41.551 [pF] = Cee-Equivalent Energy Capacitance
77.946 [pF] = Cdc-Low Frequency Capacitance
13.43 [mils] = Skin Depth
32.374 [pF] = Topload Effective Capacitance
193.688 [Ohms] = Effective AC Resistance
376 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
33.05 [kHz] = Primary Resonant Frequency
34.81 [% high] = Percent Detuned
0 [deg °] = Angle of Primary
40.25 [ft] = Length of Wire
2.97 [mOhms] = DC Resistance
0.358 [inch] = Average spacing between turns (edge to edge)
0.926 [ inch] = Proximity between coils
0 [inch] = Recommended minimum proximity between coils
40.691 [µH] = Ldc-Low Frequency Inductance
0.24227 [µF] = Cap size needed with Primary L (reference)
0 [µH] = Lead Length Inductance
552.257 [µH] = Lm-Mutual Inductance
0.18 [k] = Coupling Coefficient
0.155 [k] = Recommended Coupling Coefficient
5.56 [half cycles] = Number of half cycles for energy transfer at K
82.34 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=10, major=36, height=52, topload


« Last Edit: March 06, 2021, 05:14:32 AM by fh89 »

Offline davekni

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Re: Coil destroyed at 4ms on-time.
« Reply #56 on: March 06, 2021, 06:33:58 AM »
Yes, I suspect it was local secondary breakdown where voltage/turn is highest due to coupling.  Unfortunately, reducing coupling is likely to reduce long-arc performance.  It will reduce how low the primary can be tuned while still generating enough voltage to start an arc.  Others here may have more specific experience.  For short on-times, I think there can be advantages to lower coupling.  I can't think of any advantages with long on-times.  I had to reduce my DRSSTC coupling from 0.157 to 0.14 and add more resin layers to fix secondary arcing.  In my case, arcing from ~1/3rd of the way up to ground guard ring.  Would love to have 0.18 coupling, but my 160mm secondary diameter limits getting there.

That PTFE wrap may have induced the failure.  I've found (the hard way) that thin trapped air in areas of high AC electric field makes breakdown more likely.  I only half-understand why.  With thicker insulation material, the mechanism is more clear.  With a thin layer like your PTFE, it isn't as obvious to me.  It may be a combination of trapping heat and trapping any tiny bits of corona discharge, allowing the resulting slight insulation degradation to accumulate into a failure.  I've seen that on small HV projects myself even with thin layers over a thin air gap.

You are left with the same quandary that I had:  How much to reduce coupling and how much to rely on other improvements.  If you gambled on just leaving off the PTFE wrap next time (and perhaps thicker resin at the bottom), there is a lot of work making a new secondary that could still end up with the same failure.  Perhaps that combined with a slight reduction in coupling.

If you do reduce coupling, I suggest doing so by increasing primary inside diameter if that isn't too hard mechanically.  Do you have enough margin to remove the inside turn without running out of tuning range?  The reason to lower coupling this way is that it spreads out the field along the secondary.  Volts/turn will reduce more for a given reduction in coupling.

Such failures sure are frustrating.  But they are always part of pushing limits.  Good luck with your secondary rebuild!
David Knierim

Offline alexhanyuan

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Re: Coil destroyed at 4ms on-time.
« Reply #57 on: March 06, 2021, 06:49:27 AM »
Nice work! As nasty as that looks, you should be able to clean that up no problem. I've had no problems doing solder splices in the middle of my secondary. Just coat it back up with several thick layers of epoxy.

I didn't realize that was PTFE wrap on the bottom of your secondary. I half agree with davekni; it looks like your epoxy layer is relatively thin and the PTFE delayed the failure.

Keep the updates coming!

Offline fh89

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Re: Coil destroyed at 4ms on-time.
« Reply #58 on: March 06, 2021, 08:27:54 AM »
Quote
That PTFE wrap may have induced the failure.  I've found (the hard way) that thin trapped air in areas of high AC electric field makes breakdown more likely.  I only half-understand why.  With thicker insulation material, the mechanism is more clear.  With a thin layer like your PTFE, it isn't as obvious to me.  It may be a combination of trapping heat and trapping any tiny bits of corona discharge, allowing the resulting slight insulation degradation to accumulate into a failure.  I've seen that on small HV projects myself even with thin layers over a thin air gap.

This explanation makes sense to me. The PTFE layer is actually relatively thick at .093" I could definitely see how it would trap heat and concentrate corona in small gaps. That stupid piece of plastic cost $275 just to end up destroying what it was intended to protect! Oh well, lesson learned!

Quote
Unfortunately, reducing coupling is likely to reduce long-arc performance.  It will reduce how low the primary can be tuned while still generating enough voltage to start an arc.  Others here may have more specific experience.  For short on-times, I think there can be advantages to lower coupling.  I can't think of any advantages with long on-times.  I had to reduce my DRSSTC coupling from 0.157 to 0.14 and add more resin layers to fix secondary arcing.  In my case, arcing from ~1/3rd of the way up to ground guard ring.  Would love to have 0.18 coupling, but my 160mm secondary diameter limits getting there.
Quote
You are left with the same quandary that I had:  How much to reduce coupling and how much to rely on other improvements.  If you gambled on just leaving off the PTFE wrap next time (and perhaps thicker resin at the bottom), there is a lot of work making a new secondary that could still end up with the same failure.  Perhaps that combined with a slight reduction in coupling.

Well assuming the PTFE layer contributed to or outright caused the failure, and considering that reducing the coupling will reduce performance and may not be necessary, maybe I will just rewind it the same height and like you said, leave out the teflon and add a few extra coats of epoxy on the bottom.

Quote
If you do reduce coupling, I suggest doing so by increasing primary inside diameter if that isn't too hard mechanically.  Do you have enough margin to remove the inside turn without running out of tuning range?  The reason to lower coupling this way is that it spreads out the field along the secondary.  Volts/turn will reduce more for a given reduction in coupling.
I don't have that margin the way it is now, I'm tapped all the way out. I would have to move the primary supports out, and rewind the primary from scratch. PITA factor is also increased by the liquid cooling setup- having to drain the coolant, make new coolant lines etc. Hopefully this won't be necessary and the above idea will work. However, I do think I might benefit from being able to tune the primary lower and I could add half a turn if I remade it. That or build a bigger MMC to drop the Fres.

Quote
Such failures sure are frustrating.  But they are always part of pushing limits.  Good luck with your secondary rebuild!
Thank you sir! I will get it repaired and working again soon. I was expecting failure at some point for sure, but was expecting it to be the MMC or IGBTs!


Quote
Nice work! As nasty as that looks, you should be able to clean that up no problem. I've had no problems doing solder splices in the middle of my secondary. Just coat it back up with several thick layers of epoxy.
Thanks! I haven't decided if I am going to attempt to repair it or just rewind the whole thing. You guys think a splice would hold up on a coil of this power level? Seems to me like the slight imperfection would lead to heavy corona at the splice point and quick re-failure? It would certainly be a ton easier to splice the wire and only have to re-wind the last 1/4 or so of the coil. I'd give this a shot if the consensus is that it will hold up.


Quote
I didn't realize that was PTFE wrap on the bottom of your secondary. I half agree with davekni; it looks like your epoxy layer is relatively thin and the PTFE delayed the failure.
The epoxy was 3 coats of famowood glaze coat- used nearly a gallon on the coil! Apparently even that was not enough though!

I think Dave was saying that possibly the PTFE actually caused the failure by trapping heat and causing uneven corona. I think his explanation makes sense. A classic example of poor engineering, fixing one problem and causing another with the solution! Lesson learned the hard way!
« Last Edit: March 06, 2021, 08:37:01 AM by fh89 »

Offline davekni

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Re: Coil destroyed at 4ms on-time.
« Reply #59 on: March 06, 2021, 06:24:15 PM »
How symmetric is your secondary coil?  Repair may be possible if you can install it upside down.  Voltage stress is lower at the top, so may be able to handle the patches.
David Knierim

Offline Hydron

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Re: Coil destroyed at 4ms on-time.
« Reply #60 on: March 06, 2021, 08:51:06 PM »
Ouch, that's a decent scorch mark!

I second davekni's suggestion - was thinking of making the same one before I caught up to his post!

My other question would be how much would the frequency change if you just chopped off the damaged section? If the IGBTs can take it, higher frequency could actually give you some more margin on the primary primary tap position.

Finally, I'm not sure thick epoxy will help a lot - you're never going to get all the way under or between each turn, and if heating of the secondary is significant (which it may be at these power levels) then a thicker coat could actually be worse. If the issue is turn-to-turn breakdown then there may not be an easy fix beyond lower coupling or a spaced winding (which is not simple to pull off).

Offline davekni

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Re: Coil destroyed at 4ms on-time.
« Reply #61 on: March 06, 2021, 09:15:09 PM »
Good point about thermal expansion issues with thicker resin.  I think the PTFE ring was intended to limit arcing from primary to secondary.  My thought of thicker resin was an alternative way to prevent primary-to-secondary arcing.  I agree with Hydron that thicker resin doesn't help with secondary winding-to-winding breakdown.  Hopefully removing the PTFE ring will be sufficient to prevent that.

Some form of thick insulation on the inner primary winding may be another option.  There is much less issue of trapped air gap there, as there is little field along any air gap, only through its thickness.  Any corona there can't be worse than no insulation.  (My DRSSTC primary is litz wire between two polycarbonate plates with silicone RTV filling the inner diameter, with forced air cooling from below.)

Yes, shortening the secondary by removing the damaged part came to my mind too.  If you decide to scrap the existing secondary, it could be fun to experiment with the short version first.
David Knierim

Offline Hydron

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Re: Coil destroyed at 4ms on-time.
« Reply #62 on: March 06, 2021, 09:21:44 PM »
I would also be wary about thick insulation on the primary - too much and it will increase the field across the air-gap (the higher dielectric constant of the insulator means that it has less electric-field per unit distance than air, concentrating the field across the airgap). If there wasn't a primary-to-secondary arc then I'd leave the primary well enough alone (well, except for the purpose of changing the coupling).

Offline Mads Barnkob

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Re: Coil destroyed at 4ms on-time.
« Reply #63 on: March 06, 2021, 09:48:37 PM »
Its great to see you are pushing the limits and finding a few edges here and there, then go on to expand the distance to edge and keep pushing!

I would dare to say that "failure at the lower 20%" on the secondary coil is a old, but not well-known/well-explained problem. It has been described earlier by Steve Ward/Conner as a "whiplash" problem, I tried to gather as much information on it as possible in the tesla coil secondary coil article (scroll down to "Spark loading during ground strikes") and Secondary coil protection and the whiplash effect (scroll down to "Secondary coil protection and the whiplash effect") in the DRSSTC design guide.

Kizmo made a lathe rig to make a grove in the secondary form to get it spaced wound, to get a higher voltage-per-turn ratio and as far as I know he never destroyed that secondary coil...

Dr.Spark is one of the few coilers that went completely over-board with varnishing secondary coils. He would do 30-40 layers of polyurethane and sand in-between ever 5-10 layers to remove bubbles. I think he later on did some epoxy pour secondary's that almost looked like it was covered in glass. I do not think he ever destroyed a secondary coil. But on the other hand, he properly did not run the coils as hard as Kizmo, Terry, Eric Goodchild and Frederick here with his massive 4ms on-time.

Just having the coil running for so long at 3 ms is a great achievement!
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Offline davekni

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Re: Coil destroyed at 4ms on-time.
« Reply #64 on: March 06, 2021, 09:54:31 PM »
I certainly agree that too much insulation on the inner primary turn would reduce air gap significantly and thus increase field.  A smaller amount of insulation can increase the effective radius of the primary inner turn, thereby reducing peak field, besides adding insulation.
David Knierim

Offline fh89

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Re: Coil destroyed at 4ms on-time.
« Reply #65 on: March 06, 2021, 11:30:27 PM »
How symmetric is your secondary coil?  Repair may be possible if you can install it upside down.  Voltage stress is lower at the top, so may be able to handle the patches.
Unfortunately it is asymmetric. The top end winding stops 5 or so inches from the top
 

The endcaps are different too with the top one having a single threaded rod for the toroid mount and the bottom having two threaded rods for bolting to the primary. The mounting holes were hand drilled, so they probably won't line up if I swap them.


I think I'm goin to go ahead and try to splice the secondary wire and try to save it before scrapping the whole thing and starting over. The splice will be about 5" up from the primary. I might drop the coupling just a tad too to about .157

I already have the secondary coil form cleaned up pretty well.

This is the damage with all of the bad turns removed


Closeup of melted copper embedded in secondary


After some scrubbing with an acetone soaked rag


Did some scraping with a chisel to remove burned PVC and embedded copper.


Some of those chunks are really deep in there.


After sanding with 60, 100, 220 grit sandpaper




Quote
My other question would be how much would the frequency change if you just chopped off the damaged section? If the IGBTs can take it, higher frequency could actually give you some more margin on the primary primary tap position.

Finally, I'm not sure thick epoxy will help a lot - you're never going to get all the way under or between each turn, and if heating of the secondary is significant (which it may be at these power levels) then a thicker coat could actually be worse. If the issue is turn-to-turn breakdown then there may not be an easy fix beyond lower coupling or a spaced winding (which is not simple to pull off).

I had to remove just over 6" of windings, so frequency would go up quite a bit. The coupling would be way off too. I think I'm going to try to splice the wire and fix it, but rewind an inch higher to reduce coupling a bit and allow a greater primary to secondary clearance. Between this and leaving out the PTFE, I think it may be enough to allow me to properly melt my MMC instead of the secondary!


Quote
Its great to see you are pushing the limits and finding a few edges here and there, then go on to expand the distance to edge and keep pushing!
I am for sure expecting to break things pushing limits like this! Very interesting when things you are not expecting break first! Not sure when I will be happy with the performance- I would like at some point to call it a completed coil.

Quote
I would dare to say that "failure at the lower 20%" on the secondary coil is a old, but not well-known/well-explained problem. It has been described earlier by Steve Ward/Conner as a "whiplash" problem, I tried to gather as much information on it as possible in the tesla coil secondary coil article (scroll down to "Spark loading during ground strikes") and Secondary coil protection and the whiplash effect (scroll down to "Secondary coil protection and the whiplash effect") in the DRSSTC design guide.

Very interesting stuff there. My RF ground is a dedicated 8' ground rod located about 10' away from the coil. It is connected by 1" wide copper braid about 20' long. Maybe my ground is too low impedance allowing "whiplash?" Maybe I could run the coil with the breakout point pointed straight up to reduce heavy ground strikes.

Quote
Kizmo made a lathe rig to make a grove in the secondary form to get it spaced wound, to get a higher voltage-per-turn ratio and as far as I know he never destroyed that secondary coil...

Dr.Spark is one of the few coilers that went completely over-board with varnishing secondary coils. He would do 30-40 layers of polyurethane and sand in-between ever 5-10 layers to remove bubbles. I think he later on did some epoxy pour secondary's that almost looked like it was covered in glass. I do not think he ever destroyed a secondary coil. But on the other hand, he properly did not run the coils as hard as Kizmo, Terry, Eric Goodchild and Frederick here with his massive 4ms on-time.

This is some stuff to consider if I end up needing to rebuild the secondary from scratch. Maybe my repair and modifications will hold up, we will see!

Quote
I certainly agree that too much insulation on the inner primary turn would reduce air gap significantly and thus increase field.  A smaller amount of insulation can increase the effective radius of the primary inner turn, thereby reducing peak field, besides adding insulation.

There is an 1/8" thick polycarbonate disc covering the primary (the idea here was to help prevent primary strikes). This didn't help with primary-to-secondary arcing when the secondary started at the same height as the primary, but with me raising the secondary first turn height, the primary-to-secondary distance is basically doubled and this disc will now be between the primary and secondary and at least increase the creepage distance.



Offline fh89

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Re: Coil destroyed at 4ms on-time.
« Reply #66 on: March 15, 2021, 05:54:33 PM »
Update on the secondary repair:

I tried my best to do a half-lap splice on the 23g magnet wire . It took several tries to get it lined up somewhat decently, then I sanded the rough edges and tried to even it out as much as possible.


Closeup of splice:


I rewound the secondary a little higher than the primary. New k should be .155


Coated the new windings with Famowood Glaze coat epoxy:



Really not sure if this will hold up, but we will find out this weekend!

Offline davekni

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Re: Coil destroyed at 4ms on-time.
« Reply #67 on: March 15, 2021, 06:14:13 PM »
I'd say that is an impressive splice.  Good luck with testing!
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC
« Reply #68 on: March 16, 2021, 03:42:59 AM »
Quote
I'd say that is an impressive splice.  Good luck with testing!
Thanks, ha ha. It looks good to the naked eye, but the magnified view makes me nervous!

Got the coil back together. The secondary first turn is now 1.75" higher than the primary.
 

This is how the splice looks to the naked eye.


Magnified 10x



I'm not going to be surprised if this burns up almost immediately, but it only cost $30 for the 1lb spool of magnet wire to try out this repair.
« Last Edit: March 16, 2021, 03:48:10 AM by fh89 »

Offline davekni

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Re: BrOdin coil; the swole DRSSTC
« Reply #69 on: March 16, 2021, 04:32:07 AM »
Yes, I see the tight spacing.  Too late now, but I would have left an extra small gap in winding pitch on either side of the splice.  It may be OK, but could be susceptible to a turn-to-turn arc at the splice.  I suggest running low repetition rate initially, examining the splice after each test before increasing power.  If an arc forms there, you might catch it before burning all the way around the turn.  Perhaps you could remove one turn, cut out the existing splice, and form a new splice with a half-pitch added gap on each side.

Good luck!
David Knierim

Offline Hydron

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Re: BrOdin coil; the swole DRSSTC
« Reply #70 on: March 16, 2021, 10:38:34 AM »
On the other hand, if the splice works with the tight spacing then visually it looks great for a repair!

Offline fh89

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Re: BrOdin coil; the swole DRSSTC
« Reply #71 on: March 20, 2021, 08:27:02 AM »
Well guys, I fired the repaired coil up tonight and... It lives!

I built a 2x2 "Tesla Table" to get it up higher off the ground. Human for scale.




After a few brief test runs, I said f-it, we're going full send. Cranked it up to 15ms and let 'er rip.

15' foot ground strike


Another ground strike


Some streamers


Racing sparks and flashover, but coil survived!


Vid at 15ms, 10Hz. There is some weird frame-rate interpolation issue happening here with the gopro, it doesn't look this slow in real life.

Some low res phone video



I want to try it again at 3ms and 50Hz, but that dramatic of a change requires re-tuning. Maybe tomorrow
« Last Edit: March 20, 2021, 08:44:29 AM by fh89 »

Offline acobaugh

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #72 on: March 20, 2021, 06:12:28 PM »
Saw the videos on youtube first thing this morning. You really have no sense of scale. It just looks like a table top coil with a small step ladder next to it. Good job on the splice. You gotta figure, worst thing that can happen is it burns up a second time!

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #73 on: March 20, 2021, 08:33:09 PM »
Quote
You really have no sense of scale. It just looks like a table top coil with a small step ladder next to it.
It really does look like a smaller coil in some of these. The vertical breakout point one in particular looks almost tilt-shifted. It's funny because the primary is literally over shoulder height on me and I'm 5'10".

Quote
Good job on the splice. You gotta figure, worst thing that can happen is it burns up a second time!
Quote
On the other hand, if the splice works with the tight spacing then visually it looks great for a repair!
Thanks guys! I think I will have to eventually, there's already some carbon tracking from the flashover. Watching the video where it happened in slow-mo, I think an arc directly hit the secondary. Might have to go back to a longer breakout point to prevent this.

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #74 on: March 21, 2021, 02:35:02 AM »
Was there any breeze?  I've noticed that wind can affect arc behavior - which way they tend to head.  (I don't run if there's much wind, as my secondary and top-load are only set in place, not fastened.)  I'm wondering if wind could have caused the arc back to a lower primary point, or at least made that more likely.

Nice performance!
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #75 on: March 22, 2021, 06:42:22 AM »
Quote
Was there any breeze?  I've noticed that wind can affect arc behavior - which way they tend to head.  (I don't run if there's much wind, as my secondary and top-load are only set in place, not fastened.)  I'm wondering if wind could have caused the arc back to a lower primary point, or at least made that more likely.

It's funny that you mention that, because although it was calm at ground level, I think the coil being so tall when it is on the stand put it into light breeze because I did notice the blurry spark effect and the sparks were being pushed towards the secondary, especially at lower pulse widths.

I ended up killing the secondary again last night, this time I think it is from the direct secondary hits puncturing the insulation and shorting a turn. It failed in a different area than the splice and it is only two turns shorted. but I am going to rewind the secondary from scratch and try to optimize the design a bit more with a lower impedance and longer winding length. I think I am also going to double the MMC or build a completely new one with a higher Arms and 1+ uF capacitance.

Offline Hydron

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #76 on: March 22, 2021, 10:46:13 AM »
If V/turn is really an issue then you could try spacing the turns with nylon monofilament fishing line (may need to reduce wire diameter to keep turn number appropriate when spaced out a bit).
Might not help a lot though if the problem is direct hits from streamers (which won't care about your insulation or spacing!).

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #77 on: March 22, 2021, 07:02:42 PM »
Taller secondary will also lower coupling, unless diameter is increased proportionately.  With windings spread out a bit, perhaps you could wind all the way to the bottom again to get coupling back up.

Have you considered a larger top-load?  That would help make the field more uniform down the secondary, which should reduce strikes to the secondary.  It should also help with longer arcs.  The larger top-load capacitance supports longer arcs before resonant frequency drops too far below primary frequency.  Even if building a new nice-looking toroid is too hard/expensive, it would be fun to experiment with a cheap hack top-load addition on top of your existing toroid.  Something like a sheet of 4x8' styrofoam insulation sheet rounded with a hot-knife and covered with aluminum foil.  Would look odd, but might get you another couple feet of arc length.  That might be something to try along with your planned lower-inductance secondary.
David Knierim

Offline Uspring

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #78 on: March 23, 2021, 05:56:26 PM »
Sad to hear that your secondary was damaged again. It is a really remarkable coil ranking near or at the top of in terms of power for QCW types. I hope you get it running again soon. Any chance you can take high fps movies of it? It would be very interesting to see how much gain in arc length you get from these long on times.

I think, that spacing the secondaries winding at the bottom will decrease coupling. Coupling depends much on the overlap of primary and secondary fields and winding spacing will decrease it. I haven't calculated the effect, though.

I found Mads remarks and links to the whiplash effect interesting. How much the voltage gradient along the secondary is affected depends much on the speed of voltage change of the top load during a ground strike. From Hydrons top load measurements a typical value would be maybe 100 kV/us. That voltage jump travels down the secondary at a speed of about 400 km/s, so the jump is about 40 cm long. That means a 100 kV jump along 40 cm length. Quite a lot but it doesn't last very long.

The jump travelling speed can be estimated, by calculating or measuring the secondary resonance frequency without a top load. The coil is then a quarter wave resonator, so that frequency and wavelength is known. From this the speed of the wave can be calculated.

Hydron has made some measurements of secondary bottom currents. Whiplashes could be nicely observed there. AFAIK, there weren't any ground strikes in his last data set.

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #79 on: March 24, 2021, 02:49:42 AM »
To the extent that top-load and primary/strike-rail diameters are large compared to secondary length, there should be minimal whiplash.  Field up the primary will be roughly uniform, the field between two parallel plates of an air-dielectric capacitor.  Of course, in a real coil the diameters aren't semi-infinite.  Still, the whiplash voltage should be much less than would be experienced by a coil with no top-load.  I suspect that electric field non-uniformity up the secondary is driven more by magnetic coupling from the primary than from top-load voltage transients.
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #80 on: March 24, 2021, 06:48:44 AM »
Quote
If V/turn is really an issue then you could try spacing the turns with nylon monofilament fishing line (may need to reduce wire diameter to keep turn number appropriate when spaced out a bit).
Might not help a lot though if the problem is direct hits from streamers (which won't care about your insulation or spacing!).
In this case, I think it was streamer puncture.
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I've been playing around with the numbers in JAVATC including space-winding, but figuring out the best compromise between frequency, reactance at resonance, winding length and coupling is not easy.

 
Quote
Have you considered a larger top-load?  That would help make the field more uniform down the secondary, which should reduce strikes to the secondary.  It should also help with longer arcs.  The larger top-load capacitance supports longer arcs before resonant frequency drops too far below primary frequency.  Even if building a new nice-looking toroid is too hard/expensive, it would be fun to experiment with a cheap hack top-load addition on top of your existing toroid.  Something like a sheet of 4x8' styrofoam insulation sheet rounded with a hot-knife and covered with aluminum foil.  Would look odd, but might get you another couple feet of arc length.  That might be something to try along with your planned lower-inductance secondary.
This has crossed my mind too, but as silly as it sounds, I am hesitant to use anything other than the spun toroid after the ridiculous amount of money I spent on it. Maybe I would be ok with a ring-type toroid on top of the spun one. I'll have to give this some more thought.

Quote
Sad to hear that your secondary was damaged again. It is a really remarkable coil ranking near or at the top of in terms of power for QCW types. I hope you get it running again soon
Thanks, I appreciate that! Don't worry, I will get it fixed up and upgraded soon.

Quote
Any chance you can take high fps movies of it? It would be very interesting to see how much gain in arc length you get from these long on times.
Unfortunately the best camera I own currently is a gopro hero 8. It can shoot 120fps I think, but it isn't great in low light. I would love to get some high-quality slow-mo video. I will ask around when I'm back up running.


Quote
I think, that spacing the secondaries winding at the bottom will decrease coupling. Coupling depends much on the overlap of primary and secondary fields and winding spacing will decrease it. I haven't calculated the effect, though.

I found Mads remarks and links to the whiplash effect interesting. How much the voltage gradient along the secondary is affected depends much on the speed of voltage change of the top load during a ground strike. From Hydrons top load measurements a typical value would be maybe 100 kV/us. That voltage jump travels down the secondary at a speed of about 400 km/s, so the jump is about 40 cm long. That means a 100 kV jump along 40 cm length. Quite a lot but it doesn't last very long.

The jump travelling speed can be estimated, by calculating or measuring the secondary resonance frequency without a top load. The coil is then a quarter wave resonator, so that frequency and wavelength is known. From this the speed of the wave can be calculated.

Hydron has made some measurements of secondary bottom currents. Whiplashes could be nicely observed there. AFAIK, there weren't any ground strikes in his last data set.

Quote
To the extent that top-load and primary/strike-rail diameters are large compared to secondary length, there should be minimal whiplash.  Field up the primary will be roughly uniform, the field between two parallel plates of an air-dielectric capacitor.  Of course, in a real coil the diameters aren't semi-infinite.  Still, the whiplash voltage should be much less than would be experienced by a coil with no top-load.  I suspect that electric field non-uniformity up the secondary is driven more by magnetic coupling from the primary than from top-load voltage transients.


I'm not sure whiplash or flashover/racing sparks contributed to either of my secondary failures, so I think I am ok in that regard. I just need to keep the streamers away from the secondary!

I'm also considering modding my UD+ to run 3000A peak (along with new MMC and secondary).

For the new MMC, I've been looking at 4CAYUD3220AA3J https://content.kemet.com/datasheets/KEM_F3042_C4C_AXIAL.pdf (.22uF 3kV 12Arms) .  5 series 25 strings 125 caps 1.1uF 300Arms 15kV for $566.58. Any opinions on these caps?

« Last Edit: March 24, 2021, 07:12:49 AM by fh89 »

Offline Uspring

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #81 on: March 24, 2021, 01:24:37 PM »
@davekni:
I think we are looking at different extremes of the same issue. I am considering secondary surface charges only and am neglecting top load charges. You are doing vice versa. Presumably both type of charges need to be added in their effect.

I completely agree on the strong effect of induced voltages from the primary. The induced voltage is V = M * dIpri/dt, with M being the mutual inductance. Numerically we have M=0.55mH, Ipri=2000A and f about 33kHz for fh89s coil. That amounts to 230kV. This voltage is generated around perhaps the lower third of the coil. On top of that voltage is that produced from the secondaries current. How these add up depends on the relative phase between primary and secondary current. This is hard to predict, since it depends on the tuning, which varies with arc load.


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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #82 on: March 24, 2021, 05:07:33 PM »


That'll buff right out!

If it is as suspected a secondary strike then not a lot more I can suggest other than the longer breakout point, and possible putting more attractive streamer targets within range. Wind is certainly a killer as well - a decent breeze wrecks performance and makes the streamers go all over the place.

Secondary looks fixable again with a bit of surgery too, worth doing even if only as a spare.

What is the reason you're looking at a beefier MMC? Is the current rating of the existing one a bit suspect, or are you looking for a different capacitance/voltage rating? Could be that it can be pushed harder than expected, especially if you're looking at conservative ratings (e.g. for long life, at high ambient temperatures).
« Last Edit: March 24, 2021, 05:12:57 PM by Hydron »

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #83 on: March 24, 2021, 06:19:23 PM »
Quote
If it is as suspected a secondary strike then not a lot more I can suggest other than the longer breakout point, and possible putting more attractive streamer targets within range. Wind is certainly a killer as well - a decent breeze wrecks performance and makes the streamers go all over the place.
Yeah, I think I had issues when running raised up off the ground and lower on-times throwing it out of tune causing shorter streamers to hit the secondary. It's a real PITA having to retune every time I want to increase or decrease the on-time significantly.

 
Quote
Secondary looks fixable again with a bit of surgery too, worth doing even if only as a spare.
Yeah it is fixable, but the coilform cost $400 so I'm not really wanting to buy another one. I'm just going to re-use it and wind it from scratch.

Quote
What is the reason you're looking at a beefier MMC? Is the current rating of the existing one a bit suspect, or are you looking for a different capacitance/voltage rating? Could be that it can be pushed harder than expected, especially if you're looking at conservative ratings (e.g. for long life, at high ambient temperatures).
Yes, the RMS current rating of the MMC is only 70A, and at 2000A primary current limit, I'm pushing 547Arms at 15% duty cycle. If I bump the pri limit to 3000A, I'm looking at 822Arms, so I definitely will need a beefier MMC. I also wanted to try a lower impedance primary design with a higher capacitance value.

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #84 on: March 24, 2021, 10:35:43 PM »
I'd guess that the pictured damage event was initiated by a strike from the top, but that most of the burning came from shorted-turn current after the initial strike compromised insulation and formed plasma there.  Or it could be an arc formed from ground or primary to that point after the initial strike from top.  This is just my guess.  Others may have more experience in this area.

Yes, re-tuning is a nuisance, but necessary.  (My re-tuning is by connecting or removing banks of MMC, as my primary is fixed 4 turns of litz wire.)

I like Hydron's idea of fixing.  Run more experiments with more possible faults before bothering to rewind.  However, the wire was likely cheap compared to the form, so perhaps rewinding makes sense.

At high currents, IGBT forward drop looks more resistive, so power increases as current squared.  3000A is at least doubling IGBT power.  You might consider 2500A first before making such a large jump.

Yes, you have a beautiful toroid!  Aesthetics are lacking in most of my projects.

David Knierim

Offline Mads Barnkob

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #85 on: March 25, 2021, 01:36:33 PM »
Thumbs up for chasing the outer limits of what is physically possible with DRSSTC   8)

As DaveKni mentions, a bigger toroid would suit the coil better. I know its a very nice and very large toroid you have. I am a sucker for matching secondary winding length to toroid major diameter and secondary coil diameter to toroid minor diameter.

Regarding the 4CAYUD3220AA3J capacitors, seems to be a little "worse" than the famous CDE 942C series capacitors. For a coil this size I would recommend looking at large GTO snupper capacitors in the 1-5uF range. With M5 threaded connections and "heat sink" plates inbetween them, you can dissipate a lot more power in those than a 100+ cap MMC.

I ran your capacitor through the Tesla coil MMC calculator and I do not think that your proposed MMC is worth the money.
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Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #86 on: March 25, 2021, 04:16:10 PM »
Quote
At high currents, IGBT forward drop looks more resistive, so power increases as current squared.  3000A is at least doubling IGBT power.  You might consider 2500A first before making such a large jump.
I've seen other coils running cm600ha-24h at 3500 or even 4000A primary current, so I was actually thinking 3000 was somewhat conservative.

Quote
Thumbs up for chasing the outer limits of what is physically possible with DRSSTC   8)
Thanks, I'm just trying to have some fun with it! I'll probably get sick of blowing stuff up eventually and back it off just a tad when I find the limits of what is possible with my current setup. Hopefully one day I will have the time and $$ available to build something truly monstrous!

Quote
As DaveKni mentions, a bigger toroid would suit the coil better. I know its a very nice and very large toroid you have. I am a sucker for matching secondary winding length to toroid major diameter and secondary coil diameter to toroid minor diameter.
I might be able to live with a ring style toroid on top of the spun one. I'm giving the construction some thought.

Quote
Regarding the 4CAYUD3220AA3J capacitors, seems to be a little "worse" than the famous CDE 942C series capacitors. For a coil this size I would recommend looking at large GTO snupper capacitors in the 1-5uF range. With M5 threaded connections and "heat sink" plates inbetween them, you can dissipate a lot more power in those than a 100+ cap MMC.

I appreciate the feedback.

I would love to get my hands on some doorknob caps, I have been looking for the last month or so but I cannot find any (at least in significant quantity at a reasonable price of a suitable rating.) If anybody has a source, please let me know!

Something along the lines of AVX/TPC FPG series (FPG86X0205J seems ideal); Kemet C4DRYAQ series.

« Last Edit: March 25, 2021, 05:14:40 PM by fh89 »

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #87 on: March 25, 2021, 06:52:54 PM »
Quote
I've seen other coils running cm600ha-24h at 3500 or even 4000A primary current, so I was actually thinking 3000 was somewhat conservative.
Are these coils running close to your 15ms on-times?  Are they pulse-skipping?  If so, then go for 3000A or more.  Or start with lower on-times again.

If you don't have other plans for your MMC capacitors, you could run them until failure.  Do you know how warm they get now?  IR thermometers are great for checking temperatures, and an IR camera even better.  They can't see through plastic, however, so you would need to measure the caps from some angle with a clear view path.
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #88 on: March 26, 2021, 05:35:48 AM »
Quote
Are these coils running close to your 15ms on-times?  Are they pulse-skipping?
Good point, probably not. I will definitely start out with lower on-times. I'm not really sure I saw much length gain over 3ms, and I kind of prefer the more continuous look of higher break rates, so I might not go over that.

 
Quote
If you don't have other plans for your MMC capacitors, you could run them until failure.
I'm leaning towards using them now, but doubling the size/ Arms rating because I cannot find any doorknob caps even if I wanted to pay full price and spend $1500 bucks for new ones.

Quote
IR thermometers are great for checking temperatures, and an IR camera even better.  They can't see through plastic, however, so you would need to measure the caps from some angle with a clear view path.
I don't know how hot they get, but I pulled the bank out and they look pristine- no outward signs of overheating. I know this really doesn't completely correlate to how they are internally, but they've held up so far, and doubling the Arms rating should help. An IR camera would be awesome, but I don't have one. I will pick up a IR thermometer.

Quick question about the current limit burden resistor on the UD+
Given that the present current limit spec'd for the driver is 2000A, and the burden resistor is 5.1 Ohms, and my CT is 1024:1, that should give 2000/1024=1.95A*5.1r = 9.95v at the upper limit.
So If I want to change the limit to 3000A, I can parallel a 10 ohm resistor on top of the 5.1 equaling 3.4r, so that 3000/1024=2.93A*3.4r = 9.96v.

Is my thinking/math correct here? Is my understanding of how the current limit circuit works correct?
« Last Edit: March 26, 2021, 06:03:13 AM by fh89 »

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #89 on: March 26, 2021, 06:05:28 AM »
Quote
Quick question about the current limit burden resistor on the UD+
Given that the present current limit spec'd for the driver is 2000A, and the burden resistor is 5.1 Ohms, and my CT is 1024:1, that should give 2000/1024=1.95A*5.1r = 9.95v at the upper limit.
So If I want to change the limit to 3000A, I can parallel a 10 ohm resistor on top of the 5.1 equaling 3.4r, so that 3000/1024=2.93A*3.4r = 9.96v.

Is my thinking/math correct here?

Yes, math looks good.

The basic Seek thermal cameras run about $300.  That is what I have and found extremely useful.  I think smart-phone attachments may be available for a bit less, but I don't have a smart-phone.
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #90 on: March 26, 2021, 06:13:17 AM »
Quote
The basic Seek thermal cameras run about $300.  That is what I have and found extremely useful.  I think smart-phone attachments may be available for a bit less, but I don't have a smart-phone.
Whoa, those are neat! $250 on amazon for the smartphone attachment. Very tempting!

Quote
Yes, math looks good.
Ok cool, but is my understanding of how the current limiting circuit works correct- that I want to end up with the same voltage at the current limit?

Offline davekni

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #91 on: March 26, 2021, 07:34:22 PM »
Quote
Ok cool, but is my understanding of how the current limiting circuit works correct- that I want to end up with the same voltage at the current limit?

Yes, current sense is based on the input voltage to the LM311 comparitor.  I think you were using UD2.9 or something similar.  For UD2.9, the 10k potentiometer RV1 generates the compare voltage for current-sense.  When turned all the way up, it theoretically would be 12V * (10k / (1.8k + 10k)) = 10.17V.  Your board could easily be 9.95V due to component value tolerances.  When that voltage is reached across the sense resistor, resistor current is V/R, so primary current is 1024 * V / R for your 1024:1 current transformer.
David Knierim

Offline fh89

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Re: BrOdin coil; the swole DRSSTC Running at 15ms!
« Reply #92 on: March 27, 2021, 06:01:32 PM »
Quote
Yes, current sense is based on the input voltage to the LM311 comparitor.  I think you were using UD2.9 or something similar.  For UD2.9, the 10k potentiometer RV1 generates the compare voltage for current-sense.  When turned all the way up, it theoretically would be 12V * (10k / (1.8k + 10k)) = 10.17V.  Your board could easily be 9.95V due to component value tolerances.  When that voltage is reached across the sense resistor, resistor current is V/R, so primary current is 1024 * V / R for your 1024:1 current transformer.
Thanks, I appreciate the sanity check! Seems I came to my conclusion working backwards, but still ended up with the correct value needed for the burden resistor. 9.96v is only the value I came up with assuming the Ilim was 2000A, it probably was a little bit more (the actual Ilim)  in reality if the comparator was cutting off at 10.17. I just had the pot cranked all the way up without any sort of measurement based on the stated spec of the UD+ controller.

Offline fh89

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #93 on: April 25, 2021, 08:37:20 AM »
Brodin coil is running again!

New secondary coil 22 awg. Not sure on how many turns/fres/q/ because JAVATC predicted that I would need 9lbs to wind the entire secondary length, but I ran out of wire and used up a whole 10lb spool before the end of the secondary form length. Coupling is cranked to .185 with the first turn starting at the bottom edge of the primary tubing.



UD+ controller modified for 3000A limit


MMC doubled in size to 1.14uF



MMC cooling fans doubled



Not pushing anything too hard here, just getting retuned and seeing where we're at. Running at 1.12ms pw and 156hz prf 17.5% duty cycle

Hit 40kVA and 30kW now:

Offline Kizmo

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #94 on: April 25, 2021, 08:59:27 AM »
Such a lovely coil!

Your secondary coil failures look like what I was experiencing with the BiggerDR.

At these power levels flashovers are not always recoverable accidents  :P

Offline Hydron

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #95 on: April 25, 2021, 01:01:52 PM »
Upgrade looks pretty nice!

Have you tried longer pulse widths (like 10+ms) and lower PRFs? Could change the character of the streamers quite a bit, and it seems like the coil is likely up to it (unless it pushes IGBT die delta-T too high) if you can run 17%+ duty cycle already.

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #96 on: April 25, 2021, 07:22:13 PM »
Love watching that video in slow-motion, watching how the ground arcs develop and change shape over time!

Does anyone have a UD+ schematic or know what the feedback current capability is?  If it is like UD2.7 with a 51-ohm burden resistor, that resistor will be overheating at 17% duty cycle and 2.9A peak input (3000A / 1024:1 CT ratio).
David Knierim

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #97 on: April 25, 2021, 08:55:05 PM »
UD+ info is here:
http://classictesla.com/pslawinski/udplus.html

Looks like it is indeed 51R, if that's correct then it's running way past it's ratings, good catch!

Offline fh89

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #98 on: April 25, 2021, 09:26:32 PM »
Quote
Such a lovely coil!

Your secondary coil failures look like what I was experiencing with the BiggerDR.

At these power levels flashovers are not always recoverable accidents  :P
Thanks, I appreciate it! Yes, the flashovers can be catastrophic running at high power! Part of the price to play!

Quote
Upgrade looks pretty nice!

Have you tried longer pulse widths (like 10+ms) and lower PRFs? Could change the character of the streamers quite a bit, and it seems like the coil is likely up to it (unless it pushes IGBT die delta-T too high) if you can run 17%+ duty cycle already.

Thanks! Yes, I've run this coil up to 15ms at 10Hz - video on youtube/previous page.

Quote
Love watching that video in slow-motion, watching how the ground arcs develop and change shape over time!

Does anyone have a UD+ schematic or know what the feedback current capability is?  If it is like UD2.7 with a 51-ohm burden resistor, that resistor will be overheating at 17% duty cycle and 2.9A peak input (3000A / 1024:1 CT ratio).
Quote
UD+ info is here:
http://classictesla.com/pslawinski/udplus.html

Looks like it is indeed 51R, if that's correct then it's running way past it's ratings, good catch!

This is the EVR version of the UD+ designed to run up to 2000A. The original burdern resistor was 5.1 ohms. I paralleled a 10 ohm 3w resistor on top of the 5.1 equaling 3.4r, so that 3000/1024=2.93A*3.4r = 9.96v. So 9.96v^2/r = 99v/3.4r = 29w*.175 duty = ~5w, so maybe not too crazy over the rating?



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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #99 on: April 25, 2021, 11:37:41 PM »
Are there any PDF format (or image format such s JPG) files for the UD+ schematic?  EVR version would be great for your specific coil, or any UD+ version presuming it is close.  It would be handy to have that filed away in case other questions come up.

You'd previously discussed paralleling 10 ohms to the existing 5.1ohm resistor for over-current.  I don't know the power rating for those resistors, so don't know how much they may be past rating.  My latest comment was about feedback, not OCD.  Are you using the same 1024:1 ratio for feedback CT?  Perhaps the EVR version already has a lower-ohm feedback burden resistor to handle 2000A.  Or perhaps UD+ is expecting a higher CT ratio for 2000A?  Either way, presuming there is a separate CT input for feedback, it could be a concern for power capability inside UD+ with increasing to 3000A.
David Knierim

Offline Hydron

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #100 on: April 26, 2021, 01:05:16 AM »
Are there any PDF format (or image format such s JPG) files for the UD+ schematic?  EVR version would be great for your specific coil, or any UD+ version presuming it is close.  It would be handy to have that filed away in case other questions come up.
Software, schematic PDF, Altium SCH/PCB source and (I think) gerbers are all on the page I linked (sources hosted on github so you can just clone the repos). No idea if the EVR version uses <51R for feedback, I'd expect it to already be a smoking crater if it's not smaller than 51!

Offline fh89

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #101 on: April 26, 2021, 02:23:54 AM »
Quote
My latest comment was about feedback, not OCD.  Are you using the same 1024:1 ratio for feedback CT?  Perhaps the EVR version already has a lower-ohm feedback burden resistor to handle 2000A.  Or perhaps UD+ is expecting a higher CT ratio for 2000A?  Either way, presuming there is a separate CT input for feedback, it could be a concern for power capability inside UD+ with increasing to 3000A.

Oh the feedback resistor- my bad. Yes, it's a 1024:1 ct and the resistor is a 51 ohm:


Looks like possibly a 2w resistor? The schematic Hydron mentioned is the closest thing I know of.

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #102 on: April 26, 2021, 04:10:31 AM »
Quote
Software, schematic PDF, Altium SCH/PCB source and (I think) gerbers are all on the page I linked (sources hosted on github so you can just clone the repos). No idea if the EVR version uses <51R for feedback, I'd expect it to already be a smoking crater if it's not smaller than 51!

Poked around that link more and found PDF schematics buried a ways down in a zip file.  Thank you!  However, these don't appear to be the EVR version, as OCD reference is divided down from 5V, with ~4.1V maximum setting.  Also, the schematic shows R10 as the feedback CT burden 51-ohm 2W resistor.  fh89's image shows "R6" for the 2W 51-ohm resistor.

It is amazing that R6 hasn't burned or charred the ECB under it.  I can think of two possible reasons.  One is that the EVR version includes TVS diodes to clamp feedback voltage.  The other possibility that comes to mind is CT saturation.  Either of these possibilities might cause phase-lead to increase at high current.  Definitely warrants some exploration to see if this UD+ can correctly handle 2.9A feedback current at 17% duty cycle.  Schematics for this EVR version would be a great place to start.  Did any come with the board?  Would EVR share them electronically? 
David Knierim

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #103 on: April 26, 2021, 04:45:03 AM »
Nothing came with the board other than printed pages from Phil's webpage on the UD+ that Hydron linked. I reached out to Phil Slawinski (the designer of EVR's version of UD+) for a schematic. He suggested modding my CT. I think 48 turns should get me to where I need to be - 32*48=1536:1 = 3000/1536=1.95a

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #104 on: April 26, 2021, 06:05:44 AM »
If you can get a schematic, I'd much appreciate seeing it.  Unless there is some other difference, even 1.95A peak at 17% duty cycle is much more than the 2W resistor rating.  16W per my calculations:  0.17 * 51 * 1.95 * 1.95 * .5 = 16.48W.  It will take a little time to ramp up to 1.95A skip-pulse threshold, but I think you are spending the majority of your 17% time at the limit based on line power draw.
David Knierim

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #105 on: April 26, 2021, 06:22:01 AM »
Quote
If you can get a schematic, I'd much appreciate seeing it.  Unless there is some other difference, even 1.95A peak at 17% duty cycle is much more than the 2W resistor rating.  16W per my calculations:  0.17 * 51 * 1.95 * 1.95 * .5 = 16.48W.  It will take a little time to ramp up to 1.95A skip-pulse threshold, but I think you are spending the majority of your 17% time at the limit based on line power draw.
I will see if he's cool with sharing it. I think there must be something else we're missing because I ran the coil this whole time with a 1024:1 CT and the FB resistor was fine when I did the current limit resistor mod on the board. That photo of the resistor was taken after I smoked the secondary the second time and had the controller opened up to mod it, so it had tons of run-time at 1.95A from the CT.
« Last Edit: April 26, 2021, 07:31:02 AM by fh89 »

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #106 on: April 26, 2021, 09:26:55 AM »
If EVR hasn't touched that part, then the original schematic is, like I said, on the page I linked. The actual PDF is here: http://classictesla.com/pslawinski/UD2%20CPLD.pdf

Would be very interesting to see the primary current waveform - that resistor does NOT look like it has dissipated anywhere near the power that it in theory it has (I'm amazed it's still in existence!).

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #107 on: April 26, 2021, 08:33:49 PM »
If EVR hasn't touched that part, then the original schematic is, like I said, on the page I linked. The actual PDF is here: http://classictesla.com/pslawinski/UD2%20CPLD.pdf

Would be very interesting to see the primary current waveform - that resistor does NOT look like it has dissipated anywhere near the power that it in theory it has (I'm amazed it's still in existence!).

I can confirm the schematic is the same.

After a long chat with Phil, it turns out that I am probably only running at 1000A primary current because of the turns ratio on my CT. The max reference voltage on the comparator is 5v, and I was running 1024:1 which would give ~1A at 1000 primary amps across 5.1 ohms burden resistor - 5v triggering the OCD.

I'm going to rewind the CT so that I can actually run at 2000A. 64:32 = 2048:1 ratio and 2000/2048=.98A * 5.1ohm =4.98V.

Offline davekni

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #108 on: April 26, 2021, 09:08:59 PM »
If the schematic is actually the same, there is a 2.2k resistor from +5V to the OCD potentiometer (10k).  That gives 4.1V maximum (depending on part tolerances).  You could measure to verify.

Sounds like you have lots of room to push your coil yet harder!
David Knierim

Offline fh89

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #109 on: April 26, 2021, 11:04:06 PM »
If the schematic is actually the same, there is a 2.2k resistor from +5V to the OCD potentiometer (10k).  That gives 4.1V maximum (depending on part tolerances).  You could measure to verify.

Sounds like you have lots of room to push your coil yet harder!
I will measure it when I take it out to rewind the CT.  If that's the case, then with my modded 3.4r resistor, current limit should be closer to 2500A - 2500/2048= 1.22A * 3.4r = 4.15v.

@Kizmo - What was your primary current limit on your biggerDR coil? It was running cm600's correct?
« Last Edit: April 26, 2021, 11:08:46 PM by fh89 »

Offline fh89

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #110 on: April 27, 2021, 07:15:57 AM »
Currrent transformer is rewound to 64:32 giving 2048:1


@Davekni I measured the voltage with the pot set to max and it was 4.13 as you said. I adjusted the pot to give 3.3v on the comparator to set current limit at 2000A. 2000A/2048 =  .98A * 3.4r = 3.33v

I will still have room to crank it up to 2500A if things aren't getting extremely hot extremely quickly.

FB resistor still looks ok, and should still be ok given that the current into it should remain the same right? 
« Last Edit: April 27, 2021, 07:23:21 AM by fh89 »

Offline davekni

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Re: BrOdin coil lives again, back from the dead with upgrades.
« Reply #111 on: April 27, 2021, 07:09:26 PM »
Yes, the feedback 51-ohm resistor shouldn't run any warmer than it did in your last run (the run after lowering OCD resistor to 3.38 ohms), and even cooler with OCD set for 3.3V instead of 4.13V.  (I'm presuming OCD was set to maximum 4.13V for your last run.)

Feedback 51-ohm resistor power would have still been somewhat high in your last run.  4.13V / 3.38 ohms = 1.22A peak from CTs (1250A primary current).  Power in 51-ohm resistor at 17% duty cycle would be 0.17 * 51 * 1.22 * 1.22 * 0.5 = 6.45W.  If you were running 17% duty cycle for only a minute or two, 6W may not have been enough to scorch anything.  Or perhaps this last run wasn't hitting OCD and pulse-skipping as much as I'd estimated.
David Knierim

Offline fh89

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #112 on: May 01, 2021, 08:22:45 AM »
So I got a chance to run the coil tonight with the rewound CT and current limit set to 2000A. Nothing else changed from the last run. As soon as I turn up the PW, I get massive racing sparks, long before any large streamers even form.




I turned down the current limit pot about an 1/8 turn and it runs a lot better. I did not get a chance to experiment very much, and I have not yet been able to remove the controller and measure the voltage at the current limit comparator to see what it is set at now. I thought I saw some smoke inside the base and cut the runs short, but after looking everything over, I think it was just smoke from the frame fasteners being vaporized again. Haven't seen this issue since I made the mods to unshort the top turn and bond every frame rail together.


@davekni - I'm hoping you can explain why exceeding a certain current limit results in almost immediate racing sparks! Is there anything I can do mitigate this? Or is my best bet at this point to simply slowly turn up the current limit then back it off a touch when I get the racing sparks?

Another pic for scale. My buddy holding the tape measure is 6'2". The ladder is at 17' but did not get an arc to it this time.

« Last Edit: May 01, 2021, 08:27:55 AM by fh89 »

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #113 on: May 01, 2021, 12:40:16 PM »
The racing sparks is properly a product of too high coupling to the detuning, it simply can not get to a point where its pulled into tune before the volt/turn product on the secondary coil is exceeded.

No matter what, its still amazing results :)
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Offline fh89

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #114 on: May 01, 2021, 04:01:24 PM »
The racing sparks is properly a product of too high coupling to the detuning, it simply can not get to a point where its pulled into tune before the volt/turn product on the secondary coil is exceeded.

No matter what, its still amazing results :)


What I don't understand is why simply lowering the current limit a little bit allows it to run as intended, but raising the limit prevents any streamers from forming. I would expect changing the current limit to affect the way the coil runs at longer pw/higher prf or during ground strikes and hence higher primary current and I would understand racing sparks in those instances,  but not getting them before I can even crank the power up. Unless the primary current limit is being reached even before any long streamers are being generated?

Offline davekni

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #115 on: May 01, 2021, 06:43:09 PM »
Uspring, do you have any models that would help predict onset of racing sparks?

At high current, I'm presuming streamers don't form because you dial back pulse width once racing sparks form.  Or are you running 17% duty cycle at the higher current?  (I'm not suggesting any continued running with racing sparks, as I'd be concerned about damaging your secondary.)

As a simple model, primary coil voltage is proportional to primary current.  Higher current is higher volts/turn.  That translates to higher secondary voltage/turn near the bottom where most of the magnetic coupling is.  At some current threshold that secondary volts/turn creates enough local field to ionize air and start racing sparks.  This is a simple look, ignoring secondary current due to top load voltage.  I haven't tried to make any models for this - would be interesting to try some time.

This would also be a fun setup for controller experimenting, but I don't know of any with necessary capability.  Perhaps a current limit that starts each enable pulse at lower current and increases after an arc forms would allow higher final current without racing sparks.

BTW, as a guess, most trimmer potentiometers have about 3/4 turn of active range.  If so, your 1/8 turn is 1/6 of the range, or about 0.7 volts (4.2V / 6), so from 3.3V down to 2.6V, for 1576A OCD setting.
David Knierim

Offline TMaxElectronics

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #116 on: May 01, 2021, 11:15:06 PM »
Quote
This would also be a fun setup for controller experimenting, but I don't know of any with necessary capability.

Netzpfuscher and I have been planning to implement per-pulse ramped OCD into the UD3 for a while. It should be easy enough to do, as there is already the option to do this in QCW mode.
The question is if a ramped OCD would allow the streamer to grow from the breakout point better and thus limit voltage stress on the secondary.

But shouldn't it be easy enough to get the OCD on any other driver adjustable too? I'm thinking of a slow-ish rc LP behind the adjustment potentiometer, that also has a reset transistor across the capacitor. Maybe just an n-channel fet with the gate hooked directly to the output of the opto, so it is off when the interrupter is on. Then the OCD threshold starts at effectively 0. Obviously this would only work on pulse skip drivers as the others would just shut off immediately :P

Offline davekni

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #117 on: May 02, 2021, 12:07:03 AM »
Yes, an analog patch to UD+ could implement ramped OCD as you suggest.  Series resistor could make the starting current non-zero.  Adjusting ramp rate and starting and ending currents between experiments might be a bit tedious.  Your UD3 soft solution would be more conducive to experimenting.  Or, if someone gets around to modeling, there may be a closer starting point for an analog patch to UD+.  Without a model, I agree, we don't know for sure that more current later will help grow intended arcs without racing sparks.
David Knierim

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #118 on: May 02, 2021, 01:49:25 AM »
It might be interesting to see if there is a relationship between the secondary current and the voltage stress. In theory there should be right? after all that's only a resonant circuit too.
Then the third CT input on the UD3 (or an aux input) could be used to measure that and actively limit it to just below the maximum. Then the output power wouldn't be impacted as much.

Offline fh89

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #119 on: May 02, 2021, 05:51:07 AM »
So I ended up raising the secondary 1" to reduce coupling. That's as high as I could go short-term without major structural modifications. Javatc say this brings me from .164 to .146. I also turned the current limit back up to 2000A.
     

This reduction in coupling was enough to let me run at 2000A without racing sparks, but I smoked some silicon.

Something dies presumably at :13 seconds in the video without much drama (so hopeful it wasn't the IGBTs) and the breaker trips.  After resetting the breaker twice, something blows up at 1:10.


After getting it back inside and taking a look, it appears to be the diode bridge (Sanrex DF40AA160)
     

Hoping that's all it is, I don't see any damage to the bridge. If an IGBT dies because of overheating, would it normally just fail open without blowing up?  Is there a way to test the bridge as assembled or do I need to take it apart and test the IGBTs individually?
« Last Edit: May 02, 2021, 04:36:32 PM by fh89 »

Offline davekni

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #120 on: May 02, 2021, 06:03:41 AM »
It could be just the rectifier.  It could instead be that one or more IGBTs fried, which then fried the rectifier.  Unfortunately, that would be my guess.  Fried IGBTs likely have a collector-to-emitter short that you can measure with a meter.  If no IGBTs show as shorted, then I'd run the bridge at low voltage (say 5-50V) and scope the outputs.
David Knierim

Offline fh89

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #121 on: May 02, 2021, 08:02:38 AM »
It could be just the rectifier.  It could instead be that one or more IGBTs fried, which then fried the rectifier.  Unfortunately, that would be my guess.  Fried IGBTs likely have a collector-to-emitter short that you can measure with a meter.  If no IGBTs show as shorted, then I'd run the bridge at low voltage (say 5-50V) and scope the outputs.

Just checked, no C->E shorts! Seems like I got lucky and it's just the rectifier!

The rectifier was only rated for 40A rms and I was pulling 180A+ even before upping the primary current, not only that, but after looking closely at it, the way I had it wired was not optimal, with all of the current going through a single diode pair instead of paralleling all 3 pairs like I should have! Kind of unreal that it didn't blow up before this! Just ordered the 100A version as a replacement.
« Last Edit: May 02, 2021, 08:30:40 AM by fh89 »

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Re: BrOdin coil - High power Big sparks!
« Reply #122 on: May 02, 2021, 01:05:01 PM »
An interesting coil you got there. The combination of massive racing sparks together with only tiny topload breakout seems to imply, that the top load voltage can't alone be the source of the racing sparks. A much more likely cause is the voltage induced by the primary coil. The idea is, that there are 2 components to the magnetic field near the secondary. One component is the field caused by the current in the secondary. That field is pretty much constant along the secondary and causes a nearly linear voltage drop from the top down to the bottom.
The other field component is generated by the primary coil. That is localised around the bottom of the coil and causes an additional voltage drop there. The amount of voltage induced depends on the primary current and the geometry of the primary coil and its distance to the secondary.

The field of the primary coil drops off quite rapidly in the direction upward. The primary coil can be seen as a collection of rings, each one carrying the same current. The field of a single ring extends up to roughly its diameter, more precisely: The voltage induced in the region from the bottom to one diameter up the secondary will be about 90% of the total voltage induced along the complete secondary.

So there are two ways to avoid the induced voltage drop, which will cause the racing arcs.

1. Move the secondary away from the primary, i.e. up. The penalty for this is lower coupling.
2. Move the primary coil outward, i.e. make it larger and particularly avoid too small inner rings. That will cause the primary field to extend further up and will distribute the voltage stress along the secondary. There is also a coupling penalty, but it is less than solution 1.

You don't seem to have a large diameter primary, which possibly aggravates the arcing problem. But this just a guess and certainly a lot of work to change.

@davekni: The model implied by the above can be tackled almost analytically by calculating center fields of current rings. These are pretty simple. An even simpler model is a split of the secondary in 2 parts, one strongly coupled and the other not at all. Similar to a magnifier setup. I believe JavaTC obtains all these results but does not export them.

Offline Kizmo

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Re: BrOdin coil - insane racing sparks at 2000A OCD
« Reply #123 on: May 09, 2021, 11:53:35 AM »
It could be just the rectifier.  It could instead be that one or more IGBTs fried, which then fried the rectifier.  Unfortunately, that would be my guess.  Fried IGBTs likely have a collector-to-emitter short that you can measure with a meter.  If no IGBTs show as shorted, then I'd run the bridge at low voltage (say 5-50V) and scope the outputs.

Just checked, no C->E shorts! Seems like I got lucky and it's just the rectifier!

The rectifier was only rated for 40A rms and I was pulling 180A+ even before upping the primary current, not only that, but after looking closely at it, the way I had it wired was not optimal, with all of the current going through a single diode pair instead of paralleling all 3 pairs like I should have! Kind of unreal that it didn't blow up before this! Just ordered the 100A version as a replacement.

That would be lucky indeed if only rectifier blew up.

Your currents and duty cycles are well within the region where i started killing CM600s

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #124 on: May 15, 2021, 06:47:43 AM »
Finally got my new rectifier (11 day shipping from 50 miles away, WTF USPS?) and we are back making huge, hot streamers!  It was only the rectifier that went boom.

I am not able to lift the coil onto the stand by myself, so had to run at ground level, limiting max spark length. Anyway here are some short vids. This is the same run shot from two different angles, one a gopro hero8 2.7k@60 and a note 8 at whatever max is.






« Last Edit: May 15, 2021, 07:10:57 AM by fh89 »

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Re: BrOdin coil - High power Big sparks!
« Reply #125 on: May 15, 2021, 01:11:38 PM »
Have you tried touching the sparks at low power? At these high ontimes and low BPS it should not hurt. I would try to decrease the power so that it makes only a few inch sparks and try it. Imagine how cool would it be to touch so big streamers. But I guess that this hot plasma would burn your skin quickly.
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Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #126 on: May 15, 2021, 06:22:43 PM »
Have you tried touching the sparks at low power? At these high ontimes and low BPS it should not hurt. I would try to decrease the power so that it makes only a few inch sparks and try it. Imagine how cool would it be to touch so big streamers. But I guess that this hot plasma would burn your skin quickly.

I understand the skin effect and have touched the output from much smaller coils, even up to 4' sparks, but at much lower power levels, say 1-2kW. Those sparks leave pinhole burns in the skin and hurt a moderate amount. Holding something metal in your hand can eliminate the pinhole burns, but it still gives a strong shock feeling.

 The thought of touching the output of this monster is quite frankly terrifying, even at low on-time and BPS because of the energy in the bus caps/primary. One mistake there and it's pink mist and closed-casket.

At full power, the sparks are lighting the dry grass on fire and melting my frame bolts, I don't want to go anywhere near them, even with a 10' chicken stick. Getting hit by one of those suckers may not kill you, but I'm guessing it's a massive understatement to say it won't feel very good!



On another note, I just ordered materials to build a 14x52 toroid. Hopefully stacking that on the 10x36 will get the topload to where it needs to be for maximum spark length!
« Last Edit: May 15, 2021, 08:13:01 PM by fh89 »

Offline davekni

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Re: BrOdin coil - High power Big sparks!
« Reply #127 on: May 16, 2021, 02:13:58 AM »
Great that it was just fried rectifier diodes!  Nice performance again.  Looks like there was a little left-to-right breeze.  If you can get that sort of breeze when the coil is higher (and eventually with a larger toroid), that would be great for stretching arc length.
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Offline Kizmo

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Re: BrOdin coil - High power Big sparks!
« Reply #128 on: May 19, 2021, 08:28:52 PM »
Have you tried touching the sparks at low power? At these high ontimes and low BPS it should not hurt. I would try to decrease the power so that it makes only a few inch sparks and try it. Imagine how cool would it be to touch so big streamers. But I guess that this hot plasma would burn your skin quickly.

Total capacitance of large tesla coil is so large that sparks do hurt like hell no matter what the duty cycle is.

I have touched tiny sparks from my BiggerDR, it was not pleasant.

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #129 on: July 26, 2021, 01:23:42 AM »
I had some friends over last night for a party, so brought out the big coil for a show. I was planning on a quick demo and playing some music, but ran into an issue and had to cut the show short. Finally got a decent camera to record on:

shot on Canon EOS rebel T7

Same run shot on GoPro Hero 8:

The smoke at the end turned out to be just a coolant leak. One of the hose clamps on the primary lead coolant inlet become superheated through inductive heating and melted right through the tubing, causing coolant to spray everywhere.



This is a pretty simple fix, just cut off the melted tubing and replace clamp with zip ties.

The sparking was from an arc forming between the isolated components of the frame. The two pieces the arcing was between were at opposite ends of the ground so to speak from the isolation I did earlier in this thread. Apparently a direct hit from the coil is enough to overpower this gap even though an alternate ground path was provided by drilling/screws through each bracket and rail to punch through the anodization.

 
« Last Edit: July 26, 2021, 01:33:33 AM by fh89 »

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Re: BrOdin coil - High power Big sparks!
« Reply #130 on: July 26, 2021, 02:18:39 AM »
Quote
The sparking was from an arc forming between the isolated components of the frame. The two pieces the arcing was between were at opposite ends of the ground so to speak from the isolation I did earlier in this thread. Apparently a direct hit from the coil is enough to overpower this gap even though an alternate ground path was provided by drilling/screws through each bracket and rail to punch through the anodization.
Interesting data.  An arc strike will have some high-frequency energy on first hit.  Apparently that high-frequency current generates sufficient voltage across the inductance of the path to ground to jump your insulation gap.  Either that or the secondary arc is hitting so close to the gap that the ionized air starts the arc.  Either way, once an arc starts, the inductive loop of structure members coupled to the primary will generate high current to sustain the arc and feed it high current until the end of a burst.
David Knierim

Offline Hydron

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Re: BrOdin coil - High power Big sparks!
« Reply #131 on: July 26, 2021, 10:13:23 PM »
As far as failures go, I think you could do a lot worse!

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #132 on: September 05, 2021, 07:34:54 AM »
Got the coil all patched up and upgraded! After running the bus voltage drop calculations on Mads' site and ending up with a nearly 100v drop, I added 10,000uF more to the bus caps, now totaling 26,800uF and bringing voltage drop down to around 20v.

Another shot for scale (I'm 5'10" 195lb):


GoPro angle

DSLR angle



« Last Edit: September 05, 2021, 07:57:46 AM by fh89 »

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Re: BrOdin coil - High power Big sparks!
« Reply #133 on: September 05, 2021, 02:06:36 PM »
Did you ever consider replacing the aluminium extrusions on top of the box with a plate of acrylic or polycarbonate? That would probably solve the issues with arcover that you are having without requiring a complete rebuild.

I have a thick sheet of Polycarbonate on top of my coil, strengthened with some of those extruded pieces (but without them touching). Like this:


That is very strong and didn't give me any issues with voltage so far

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #134 on: September 05, 2021, 06:35:39 PM »

Wow, that is a fantastic looking coil, great job on the construction! The adjustable coupling is a great idea, would have been great to have on my coil. Maybe I will do something along those lines on my next build.

For now, I'm not too worried about the arcover on the frame. It does melt some of the aluminum, but it is not serious enough to compromise the structural integrity of the frame, and it does seem to fizzle out after arcing over for a few seconds. I figure that it will either become carbonized/oxidized enough or enough material will be vaporized that it stops arcing over in that corner.

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Re: BrOdin coil - High power Big sparks!
« Reply #135 on: September 05, 2021, 08:46:04 PM »

Wow, that is a fantastic looking coil, great job on the construction! The adjustable coupling is a great idea, would have been great to have on my coil. Maybe I will do something along those lines on my next build.

For now, I'm not too worried about the arcover on the frame. It does melt some of the aluminum, but it is not serious enough to compromise the structural integrity of the frame, and it does seem to fizzle out after arcing over for a few seconds. I figure that it will either become carbonized/oxidized enough or enough material will be vaporized that it stops arcing over in that corner.

Great run! and that amount of DC bus capacitance is going to give a show if you explode and IGBT :)

So keep the cameras rolling! You have the rock and roll attitude of Tesla coiling with "enough material will be vaporized that it stops arcing over in that corner."  8)

Your secondary is much much wider than I first thought, its easy to read a measure and imagine something, but your new pictures of standing next to it....
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Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #136 on: September 06, 2021, 12:44:28 AM »

Great run! and that amount of DC bus capacitance is going to give a show if you explode and IGBT :)

So keep the cameras rolling! You have the rock and roll attitude of Tesla coiling with "enough material will be vaporized that it stops arcing over in that corner."  8)

Your secondary is much much wider than I first thought, its easy to read a measure and imagine something, but your new pictures of standing next to it....

Probably inevitable that I blow an IGBT eventually, hopefully not for a few years though!

Lol, she's a girthy beast for sure! Hard to gauge the actual size of the coil without any point of reference.

 I really need some easier way to get it higher off the ground, the stand I built is nearly impossible to get the coil on alone. I think it would really help horizontal spark length.

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Re: BrOdin coil - High power Big sparks!
« Reply #137 on: September 06, 2021, 08:13:17 AM »

Great run! and that amount of DC bus capacitance is going to give a show if you explode and IGBT :)

So keep the cameras rolling! You have the rock and roll attitude of Tesla coiling with "enough material will be vaporized that it stops arcing over in that corner."  8)

Your secondary is much much wider than I first thought, its easy to read a measure and imagine something, but your new pictures of standing next to it....

Probably inevitable that I blow an IGBT eventually, hopefully not for a few years though!

Lol, she's a girthy beast for sure! Hard to gauge the actual size of the coil without any point of reference.

 I really need some easier way to get it higher off the ground, the stand I built is nearly impossible to get the coil on alone. I think it would really help horizontal spark length.

You look to be working out quite a bit more than I do  ;D I can barely lift my secondary coil in place alone, in a safe manner where I would not scratch it, so my large coil is also too big for a single person to manipulate beyond its original physical dimensions. I have thought about making a base, in a distant future, that would be ready-made for a cheap motorcycle scissor lift like this: https://www.expondo.dk/msw-sakselift-mc-150-kg-10060972 or something similar, it would properly need a bigger foot print for stability.
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Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #138 on: September 06, 2021, 08:55:11 AM »
Quote
You look to be working out quite a bit more than I do  ;D I can barely lift my secondary coil in place alone, in a safe manner where I would not scratch it, so my large coil is also too big for a single person to manipulate beyond its original physical dimensions. I have thought about making a base, in a distant future, that would be ready-made for a cheap motorcycle scissor lift like this: https://www.expondo.dk/msw-sakselift-mc-150-kg-10060972 or something similar, it would properly need a bigger foot print for stability.

Ha ha, well I am a bit of a "gym bro", hence the "BrO"din name of my coil! My secondary is also very difficult for me to lift and install or remove from the coil base. It is relatively heavy but manageable at 45kg/100lb, but the physical dimensions make it quite difficult to grasp and maneuver. Lifting the assembled coil requires at least two people. A jack like the one you mentioned is something to think about for future builds!

Offline alexhanyuan

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Re: BrOdin coil - High power Big sparks!
« Reply #139 on: September 17, 2021, 08:23:44 PM »
Have you measured the arc current? Must be tens of amps to be doing that to the aluminum frame. Certainly not 'high voltage, but low current' anymore haha.

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #140 on: September 17, 2021, 11:41:50 PM »
Have you measured the arc current? Must be tens of amps to be doing that to the aluminum frame. Certainly not 'high voltage, but low current' anymore haha.

It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!

I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?


Offline futurist

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Re: BrOdin coil - High power Big sparks!
« Reply #141 on: September 18, 2021, 01:26:15 AM »
Check out Hydron's topload current measurements thread
https://highvoltageforum.net/index.php?topic=117.0

Offline davekni

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Re: BrOdin coil - High power Big sparks!
« Reply #142 on: September 18, 2021, 05:28:46 AM »
Quote
It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!
That's definitely my guess too.  Frame sparks often continue after tho top arc leaves the frame in your videos.

Quote
I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?
Measuring current of the secondary coil ground connection will get rather close.  Once an arc strikes, top-load voltage drops way down, so secondary current at the bottom is close to matching arc current.  My DRSSTC has a current transformer measuring secondary current, which I scope every time I run my coil.

Not worth the bother, but you could make a large CT with U-cores to measure frame current around one of the 80/20 sections.  CT would need insulation cover to avoid strikes from secondary.
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Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #143 on: September 18, 2021, 07:39:29 AM »
Check out Hydron's topload current measurements thread
https://highvoltageforum.net/index.php?topic=117.0

Amazing work there, but not something I could pull off!

Quote
It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!
That's definitely my guess too.  Frame sparks often continue after tho top arc leaves the frame in your videos.

Quote
I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?
Measuring current of the secondary coil ground connection will get rather close.  Once an arc strikes, top-load voltage drops way down, so secondary current at the bottom is close to matching arc current.  My DRSSTC has a current transformer measuring secondary current, which I scope every time I run my coil.

Not worth the bother, but you could make a large CT with U-cores to measure frame current around one of the 80/20 sections.  CT would need insulation cover to avoid strikes from secondary.

I have that Ion Physics current monitor I used for primary current measurement when setting phase lead way earlier in this thread. It will have to wait though as I burned up the secondary again tonight  :(

First had a successful run playing the Tetris theme, making huge sparks for a coil in music mode:

But then I cranked the PW and PRF all the way up and just sent it-


Me again, for spark size scale:


Another secondary coil smoked! Grrr!

The moment the streamer hit the secondary:


Damage:





« Last Edit: September 18, 2021, 08:30:09 AM by fh89 »

Offline davekni

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Re: BrOdin coil - High power Big sparks!
« Reply #144 on: September 18, 2021, 08:00:23 PM »
Quote
The moment the streamer hit the secondary:
Wow, that must be so frustrating and disappointing!  The secondary strike initiation does make for a beautiful picture, though.  Thank you for sharing that.
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Offline AstRii

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Re: BrOdin coil - High power Big sparks!
« Reply #145 on: September 18, 2021, 08:34:15 PM »
I cannot even imagine how frustrating this must be.. but then again, patience is needed when pushing the limits :)
Haven't you considered a bigger topload? Better electric field distribution might solve all your issues with racing sparks and secondary being hit.
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Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #146 on: September 18, 2021, 09:00:32 PM »
Quote
The moment the streamer hit the secondary:
Wow, that must be so frustrating and disappointing!  The secondary strike initiation does make for a beautiful picture, though.  Thank you for sharing that.

Yes, very frustrating, but I will rewind again!

It's really interesting how a small arc formed off the main streamer that was already arcing directly to the strike rail and jumped to the secondary. Here's the frame-by-frame:


Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #147 on: September 18, 2021, 09:05:03 PM »
I cannot even imagine how frustrating this must be.. but then again, patience is needed when pushing the limits :)
Haven't you considered a bigger topload? Better electric field distribution might solve all your issues with racing sparks and secondary being hit.

Yeah, it is frustrating to be sure, but like you said, it's the price to play! This isn't a tabletop coil conservatively designed to run forever!

I made a much larger 14x52" toroid that I could not get to work without major structural changes. It caused overcoupling and racing sparks, even after raising the secondary 1.5", the most I can do right now.

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Re: BrOdin coil - High power Big sparks!
« Reply #148 on: September 20, 2021, 10:38:31 AM »
Some secondaries survive many hours of run time, but eventually they all fail

Did you try using counterpoise? In my experience it seems that it directs streamers away from the coil


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Re: BrOdin coil - High power Big sparks!
« Reply #149 on: September 20, 2021, 05:07:43 PM »
You always seem to have your camera on, when something interesting happens.  ;)

Longer lasting arcs tend to curl up after some time as you can see in your slow motion video. And that can be a problem near the strike rail. Particularly if there is some wind blowing.
Often arcs follow a previous burst since it leaves a path of hot air behind, which is thinner and thus breaks down at lower voltages. This pathway isn't very stable, though, since the arcs charges repel each other, which causes the pathway to curl like a negative string tension. It is buckling in a way. Every burst in a retracing series will be a bit more curled than the previous one. Usually arcs look for the shortest path bridging a gap, but hot air relaxes this requirement.

I suggest monitoring the current from the strike rail to ground and shutting the coil off maybe for a tenth of a second, when it is hit. That will allow the air to cool off, so that the next burst will take another route. Initial routes are much straighter than the retraced ones following a previous burst.

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #150 on: September 21, 2021, 03:56:28 AM »
Some secondaries survive many hours of run time, but eventually they all fail

Did you try using counterpoise? In my experience it seems that it directs streamers away from the coil

Yeah, at this power level, any direct hit is going to pretty much instantly annihilate the secondary windings.  I need to prevent any secondary hits if I want this next one to last!

I assume you mean a separate counterpoise from my main 8' dedicated RF ground rod as a strike target so to speak in front of the coil? That's something I could try.

You always seem to have your camera on, when something interesting happens.  ;)

Longer lasting arcs tend to curl up after some time as you can see in your slow motion video. And that can be a problem near the strike rail. Particularly if there is some wind blowing.
Often arcs follow a previous burst since it leaves a path of hot air behind, which is thinner and thus breaks down at lower voltages. This pathway isn't very stable, though, since the arcs charges repel each other, which causes the pathway to curl like a negative string tension. It is buckling in a way. Every burst in a retracing series will be a bit more curled than the previous one. Usually arcs look for the shortest path bridging a gap, but hot air relaxes this requirement.

I suggest monitoring the current from the strike rail to ground and shutting the coil off maybe for a tenth of a second, when it is hit. That will allow the air to cool off, so that the next burst will take another route. Initial routes are much straighter than the retraced ones following a previous burst.


Multiple cameras always running!

That's a really good idea. I should just shut it down for a moment as soon as there's a frame/strike rail hit.


Offline futurist

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Re: BrOdin coil - High power Big sparks!
« Reply #151 on: September 21, 2021, 04:18:47 PM »
Counterpoise from wire mesh, for example I'm using insect mesh because it's easy to store it in a roll
/>
There was some discussion about using counterpoise for DRSSTC here on the forum and on 4hv. In my experience my coil performs better when used in different environments if I'm using counterpoise. On the other hand it causes high current ground strikes which fry the secondaries

Offline Intra

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Re: BrOdin coil - High power Big sparks!
« Reply #152 on: September 30, 2021, 03:43:51 AM »
My apologies if I repeat what someone may have already wrote here.

By quick glance I could say that this secondary and it's toroid isn't quite optimal.

With that secondary length and toroid length your secondary magnetic field geometry not wide enough to spark could avoid to strike in chasiss on that spark length especially when your chasiss is completely metal and whole coil is put on wood rack alowing to strike in chasiss from bottom. Different terminal angle and length, larger toroid and longer secondary could help with this issue.
It is also good to place a toroid at least on 1/2 of toroid thickness from secondary to edge of the toroid lower plane.

For 12.75 pipe you may want to try 20awg wire with 5:1 ratio so it will be about 64.11 inch of winding length.
Also, for this possible new secondary will fit 62.3x12.4 toroid.
Primary resonance frequency in transient mode good to be 10-15% lower than secondary but in freewheeling mode it better to be even 25% lower.
Coupling is 0.154
Try this calc https://tqfp.org/calculatoria/tesla/

About how much primary windings is best. If your goal not in limiting current by primary and you run your coil in freewheeling you may do even 2.5 windings with apropriate mmc.

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #153 on: September 30, 2021, 06:11:21 AM »
My apologies if I repeat what someone may have already wrote here.

By quick glance I could say that this secondary and it's toroid isn't quite optimal.

With that secondary length and toroid length your secondary magnetic field geometry not wide enough to spark could avoid to strike in chasiss on that spark length especially when your chasiss is completely metal and whole coil is put on wood rack alowing to strike in chasiss from bottom. Different terminal angle and length, larger toroid and longer secondary could help with this issue.
It is also good to place a toroid at least on 1/2 of toroid thickness from secondary to edge of the toroid lower plane.

For 12.75 pipe you may want to try 20awg wire with 5:1 ratio so it will be about 64.11 inch of winding length.
Also, for this possible new secondary will fit 62.3x12.4 toroid.
Primary resonance frequency in transient mode good to be 10-15% lower than secondary but in freewheeling mode it better to be even 25% lower.
Coupling is 0.154
Try this calc https://tqfp.org/calculatoria/tesla/

About how much primary windings is best. If your goal not in limiting current by primary and you run your coil in freewheeling you may do even 2.5 windings with apropriate mmc.

I don't disagree with anything you said, but when building a coil of this size, numerous compromises had to be made because of cost and practicality, at least for me. For example, the current secondary used an entire 10lb spool of #22 wire, a longer winding length would require buying a bigger spool and the smallest next size up I can find is an 80lb spool for $1000USD! (If anybody knows where to buy magnet wire in quantities greater  than 10lbs and less than 80, let me know.)

The Toroid is too small, I agree and have experimented with a larger one, but it causes overcoupling racing sparks, even after raising the secondary 1.5", the max I can do. The toroid was also incredibly expensive, by far the most expensive part of this build at $2000USD shipped, so I'm not in a hurry to not use it now! Definitely will go bigger on the next coil!

The coil is also at the maximum height that can fit in my garage assembled. I could store each piece separately, but it is so convenient to be able to just wheel it in and out of the garage instead of carefully packing the toroid and secondary safely away where they will not get damaged, then needing to unpack and re-assemble it every time I want to run it.

Building this coil and getting so much useful feedback from the members here has been a learning experience for sure, and I will take all these suggestions to heart when the time comes to build an even better coil!

For now at least, I've pretty satisfied with the performance of this coil, especially considering all of the design compromises and less-than-ideal specs and parts chosen! After rewinding the secondary, I will consider it a finished coil. The only other thing I am planning to crank the primary current limit up a tad to 2500A, and see if there's any noticeable performance improvement.

 

Offline Intra

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Re: BrOdin coil - High power Big sparks!
« Reply #154 on: September 30, 2021, 10:34:51 PM »
(If anybody knows where to buy magnet wire in quantities greater  than 10lbs and less than 80, let me know.)
You can wind bifilar from two 26awg from this 6290ft $58+shipping spools https://www.ebay.com/itm/251040537280
For 12.75x64.11 need about 6299ft per spool which fits wery well and it also decrease secondary heating

have experimented with a larger one, but it causes overcoupling racing sparks, even after raising the secondary 1.5"
With 36x10 toroid and 22awg 12.75x48 coil you have 78.5k secondary impedance while with 50k or less you will have longer spark on same other parameters.
With 0.15 coupling your spark will be shorter than with 0.18, but racing sparks will gone. 0.11 is too low for 12.75 pipe.
Other option to improve perfomance you may try up voltage to 800v with pfc or rewire rectifier to doubler.

The toroid was also incredibly expensive, by far the most expensive part of this build at $2000USD shipped
Toroids can be self-made from tubes https://www.lowes.com/pd/Steelworks-3-4-in-dia-x-3-ft-L-Mill-Finished-Aluminum-Round-Tube/3053653
by tube roller https://www.ebay.com/itm/224567948035
My brand new TR-60 costs me $260 instead of $470 because I found it in my town.

For 62.3x12.4 toroid tubes in Lowes should cost about $400. I'm too far from LA, maybe you know better place to buy tubes or bender arround you.

You can make toroid even with aluminium foil tape. Check "Mon Jul 16 2012, 03:08pm" post from here https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=141872

The coil is also at the maximum height that can fit in my garage assembled. I could store each piece separately, but it is so convenient to be able to just wheel it in and out of the garage instead of carefully packing the toroid and secondary safely away where they will not get damaged, then needing to unpack and re-assemble it every time I want to run it.
I store my twins on 5 level of condominium with no elevator.

Offline Duane B

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Re: BrOdin coil - High power Big sparks!
« Reply #155 on: October 01, 2021, 07:07:07 PM »
That's a great coil fh89! One to be proud of. Personally, I don't think you need to change anything.
Duane Bylund

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #156 on: October 30, 2021, 06:44:00 AM »
Brodin Coil returns from the dead yet again, this time running at 57kW peak power!


Winding jig for the 3rd secondary


1st coat of epoxy applied. Total of 3 coats applied this time.


Rebuilt and standing tall!

I cranked the primary current limit up to 2500A because YOLO, SEND IT, LFG! I am sick of burning secondary coils up, something else break please! But nothing blew up this time, guess I'll have to wait a little longer to rebuild the bridge!

New higher primary current has the coil drawing 350+ Amps from the 240V line!


From the DSLR


 From the GoPro
« Last Edit: October 30, 2021, 08:22:39 AM by fh89 »

Offline alexhanyuan

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Re: BrOdin coil - High power Big sparks!
« Reply #157 on: November 05, 2021, 12:24:35 AM »
Can't believe you're still running those 942Cs!

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #158 on: November 05, 2021, 02:56:32 AM »
Can't believe you're still running those 942Cs!

Well technically 940c's with higher Arms! They seem to be holding up so far, even at 2500A primary current limit. IIRC, the mmc is only built at 750ish Arms, so maybe these caps aren't all that bad after all?

I wanted and looked forever for some doorknob caps, but I couldn't find any with sufficient ratings in enough quantity for remotely reasonable price.

Offline Duane B

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Re: BrOdin coil - High power Big sparks!
« Reply #159 on: November 05, 2021, 08:49:30 PM »
Very impressive! Rising from the dead, or being born again, maybe you should call that coil the Phoenix?
Duane Bylund

Offline davekni

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Re: BrOdin coil - High power Big sparks!
« Reply #160 on: November 07, 2021, 08:11:19 PM »
Quote
They seem to be holding up so far, even at 2500A primary current limit. IIRC, the mmc is only built at 750ish Arms, so maybe these caps aren't all that bad after all?
If  750Arms is the capacitor rating, you are likely fine.  2500Apeak is 1770Arms during full current (pulse-skip operation) enable pulses.  750Arms corresponds to 18% duty cycle of 1770Arms.

Quote
I cranked the primary current limit up to 2500A because YOLO, SEND IT, LFG! I am sick of burning secondary coils up, something else break please! But nothing blew up this time, guess I'll have to wait a little longer to rebuild the bridge!
The quandary seems to be how to get arcs farther away from the coil while keeping your beautiful toroid.  Perhaps the solution is a large tapered breakout point, large enough to both add some capacitance and to move arcs farther away.  Perhaps a variation on something I'd suggested earlier:  Use a 2" x 4' x 8' styrofoam insulation board (or two laminated to get 4" thickness).  Cut into a tear-drop shape, 8' long to the point and 4' diameter at the other end.  Round edges and cover with foil.  Add a breakout rod extension past the point.  May need some counterweight at the round end of the teardrop to keep it balanced on top of your toroid.
David Knierim

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #161 on: November 09, 2021, 05:17:25 AM »
Quote
They seem to be holding up so far, even at 2500A primary current limit. IIRC, the mmc is only built at 750ish Arms, so maybe these caps aren't all that bad after all?
If  750Arms is the capacitor rating, you are likely fine.  2500Apeak is 1770Arms during full current (pulse-skip operation) enable pulses.  750Arms corresponds to 18% duty cycle of 1770Arms.

I appreciate the insight as always! There's more headroom than I realized on the cap rating. Hopefully it will last a decent amount of time!

Quote
I cranked the primary current limit up to 2500A because YOLO, SEND IT, LFG! I am sick of burning secondary coils up, something else break please! But nothing blew up this time, guess I'll have to wait a little longer to rebuild the bridge!
Quote
The quandary seems to be how to get arcs farther away from the coil while keeping your beautiful toroid.  Perhaps the solution is a large tapered breakout point, large enough to both add some capacitance and to move arcs farther away.  Perhaps a variation on something I'd suggested earlier:  Use a 2" x 4' x 8' styrofoam insulation board (or two laminated to get 4" thickness).  Cut into a tear-drop shape, 8' long to the point and 4' diameter at the other end.  Round edges and cover with foil.  Add a breakout rod extension past the point.  May need some counterweight at the round end of the teardrop to keep it balanced on top of your toroid.

As silly as I know this sounds, the trade off in aesthetics just isn't worth it to me. I do appreciate the creative suggestions though! Next coil will have a properly sized toroid, but I'm content now with where this one is at. I will still experiment a bit with a slightly shorter and also a very short breakout point as well as elevating the coil, but aside from that I'm calling it a finished project.

Offline Mads Barnkob

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Re: BrOdin coil - High power Big sparks!
« Reply #162 on: November 09, 2021, 07:02:44 PM »
Being from a 3 phase country, its just so unreal to see someone pull 350A from a 240VAC output!

If you have forced air cooling on the MMC, it will last a long time. A thing I thought about, was to never cut the leads of axial MMC capacitors, but curl them up in a spiral, to use as a heat sink. As 66% of heat in a axial capacitor is radiated out of the ends and especially the leads. Only 33% is radiated from the round large surface.

Can I use one of your pictures to add your coil to my list of featured coils on kaizerpowerelectronics.dk ? I think I have asked about this before, but have forgot to actually add it :)
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
https://www.youtube.com/KaizerPowerElectronicsDk60/join - Please consider supporting the forum, websites and youtube channel!

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #163 on: November 09, 2021, 08:13:33 PM »
Quote
Being from a 3 phase country, its just so unreal to see someone pull 350A from a 240VAC output!

Yes, It's quite amazing that the coil can draw so much power!


Quote
If you have forced air cooling on the MMC, it will last a long time.

I think I have that covered! Six 120mm 240V fans on the MMC


Quote
A thing I thought about, was to never cut the leads of axial MMC capacitors, but curl them up in a spiral, to use as a heat sink. As 66% of heat in a axial capacitor is radiated out of the ends and especially the leads. Only 33% is radiated from the round large surface.

I did something along these lines, I soldered the leads to a thick 1/8th" x 1/2" (3mm x 12mm) copper busbars for heatsinking of the leads:
 [ You are not allowed to view attachments ]

I give up. I tried 47 times to get this attachment to work, but for some reason it just says  [ You are not allowed to view attachments ] every time, even though the first photo above works!
Photo of MMC below


Quote
Can I use one of your pictures to add your coil to my list of featured coils on kaizerpowerelectronics.dk ? I think I have asked about this before, but have forgot to actually add it :)

Yes, please feel free to use any of my photos! I think this one is my favorite though!

 
Also, here is a photo dump of all of my construction photos (some of these photos show mistakes that were later corrected):
https://1drv.ms/u/s!Ap7oF5iAXsqR_Q4Ll1D90VbZBSRI?e=13UIZi

« Last Edit: November 10, 2021, 04:32:37 AM by fh89 »

Offline futurist

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Re: BrOdin coil - High power Big sparks!
« Reply #164 on: November 09, 2021, 11:41:16 PM »
Wow those are really impressive streamers!

That 350A current draw reminds me of mr. Photon, a plug straight to the National Grid? :D

Offline Kizmo

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Re: BrOdin coil - High power Big sparks!
« Reply #165 on: November 22, 2021, 06:55:08 PM »
This is just so cool to see!

Pulse skipping driver on a big coil, lovely!

Offline fh89

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Re: BrOdin coil - High power Big sparks!
« Reply #166 on: November 22, 2021, 07:13:14 PM »
Quote
Wow those are really impressive streamers!

That 350A current draw reminds me of mr. Photon, a plug straight to the National Grid? :D

Quote
This is just so cool to see!

Pulse skipping driver on a big coil, lovely!

Really appreciate it coming from you guys! Been busy with other projects, but hope to get the coil fired up again soon and get some more video!

Offline Kizmo

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Re: BrOdin coil - High power Big sparks!
« Reply #167 on: November 22, 2021, 07:56:40 PM »
This makes my brute force approach (BiggerDR) to seem like waste of silicon.

Offline patracy

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Re: BrOdin coil - High power Big sparks!
« Reply #168 on: November 27, 2021, 06:06:59 AM »
I've enjoyed reading about this coil.  So much that I went out and purchased a few of those CM600's myself.  Now to find a driver and a few other bits.  Maybe I can offload some of the stuff I have to start funding that build.

High Voltage Forum

Re: BrOdin coil - High power Big sparks!
« Reply #168 on: November 27, 2021, 06:06:59 AM »

 


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November 28, 2021, 04:48:04 PM
post Re: SG3525 push pull snubber calculation
[Transformer (Ferrite Core)]
PowerTech
November 28, 2021, 03:16:11 PM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ItsChloeUwU
November 28, 2021, 09:36:10 AM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
plasma
November 28, 2021, 05:32:16 AM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 28, 2021, 04:28:33 AM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ItsChloeUwU
November 28, 2021, 02:19:00 AM
post Re: Where to buy DIY or home made capacitor book(s)?
[Capacitor Banks]
huntergroundmind
November 28, 2021, 01:58:12 AM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 28, 2021, 12:53:27 AM
post Re: Driverless SSTC
[Solid State Tesla Coils (SSTC)]
davekni
November 28, 2021, 12:32:09 AM
post Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
[Solid State Tesla Coils (SSTC)]
davekni
November 28, 2021, 12:16:04 AM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ItsChloeUwU
November 27, 2021, 11:42:08 PM
post Re: Hi! 811 A tesa coil
[Vacuum Tube Tesla Coils (VTTC)]
304er
November 27, 2021, 11:32:12 PM
post Re: Hi! 811 A tesa coil
[Vacuum Tube Tesla Coils (VTTC)]
jpvvv123
November 27, 2021, 11:09:43 PM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
paulj
November 27, 2021, 10:06:41 PM
post Re: SG3525 push pull snubber calculation
[Transformer (Ferrite Core)]
PowerTech
November 27, 2021, 09:40:34 PM
post Re: SG3525 push pull snubber calculation
[Transformer (Ferrite Core)]
davekni
November 27, 2021, 08:51:05 PM
post Re: Infrastructure and Architecture
[General Chat]
Da_Stier
November 27, 2021, 08:09:50 PM
post Re: SG3525 push pull snubber calculation
[Transformer (Ferrite Core)]
PowerTech
November 27, 2021, 06:00:42 PM
post Re: Someone built Big TC
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
November 27, 2021, 05:04:46 PM
post Re: Someone built Big TC
[Spark Gap Tesla Coils (SGTC)]
304er
November 27, 2021, 04:45:14 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
Mads Barnkob
November 27, 2021, 07:59:37 AM
post Re: Contest of motor slowness, or lowness of voltage?
[Science, Research and News In Other Fields Than Electronics]
Mads Barnkob
November 27, 2021, 07:52:59 AM
post Re: FPS1000HD unboxing and first impression
[High Speed Filming]
Mads Barnkob
November 27, 2021, 07:51:01 AM
post Re: Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
[Solid State Tesla Coils (SSTC)]
Mads Barnkob
November 27, 2021, 07:47:23 AM
post Re: Infrastructure and Architecture
[General Chat]
Mads Barnkob
November 27, 2021, 07:37:57 AM
post Re: Someone built Big TC
[Spark Gap Tesla Coils (SGTC)]
Mads Barnkob
November 27, 2021, 07:21:43 AM
post Re: BrOdin coil - High power Big sparks!
[Dual Resonant Solid State Tesla coils (DRSSTC)]
patracy
November 27, 2021, 06:06:59 AM
post Re: Someone built Big TC
[Spark Gap Tesla Coils (SGTC)]
304er
November 27, 2021, 05:27:27 AM
post Re: Kind of old single piece of glass plate capacitor
[Spark Gap Tesla Coils (SGTC)]
304er
November 27, 2021, 03:19:55 AM
post Re: Kind of old single piece of glass plate capacitor
[Spark Gap Tesla Coils (SGTC)]
304er
November 27, 2021, 02:31:46 AM
post Re: Kind of old single piece of glass plate capacitor
[Spark Gap Tesla Coils (SGTC)]
304er
November 27, 2021, 02:22:20 AM
post Driverless SSTC
[Solid State Tesla Coils (SSTC)]
bismallah
November 26, 2021, 11:59:27 PM
post Infrastructure and Architecture
[General Chat]
Da_Stier
November 26, 2021, 11:27:47 PM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
klugesmith
November 26, 2021, 11:17:55 PM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
November 26, 2021, 08:24:39 PM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 26, 2021, 07:48:07 PM
post Help on my "first" SSTC (LabCoatz SSTC 2.0)- Popping transistors
[Solid State Tesla Coils (SSTC)]
TiagoBS
November 26, 2021, 07:44:25 PM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
davekni
November 26, 2021, 06:58:16 PM
post Re: 60hz synchronous motor on 50hz?
[Spark Gap Tesla Coils (SGTC)]
plasma
November 26, 2021, 05:40:37 PM
post Re: "Exploding" water
[Capacitor Banks]
MRMILSTAR
November 26, 2021, 04:39:07 PM
post Re: Kind of old single piece of glass plate capacitor
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
November 26, 2021, 04:31:20 PM
post Re: Next Gen DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Intra
November 26, 2021, 03:52:08 PM
post Re: "Exploding" water
[Capacitor Banks]
johnf
November 26, 2021, 09:17:07 AM
post Re: Kind of old single piece of glass plate capacitor
[Spark Gap Tesla Coils (SGTC)]
paulj
November 26, 2021, 08:45:34 AM
post Re: Some Starting Questions About My New DRSSTC ???
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ItsChloeUwU
November 26, 2021, 06:31:56 AM

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