High Voltage Forum
Tesla coils => Dual Resonant Solid State Tesla coils (DRSSTC) => Topic started by: Miki_407 on November 30, 2020, 11:58:29 AM
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Hello,
I am 14 years old and this is my first true drsstc. Does the secondary need to be changed? I used 0.1mm wire for it and a 75mm pvc pipe, length of windings is 14.5cm. Would it be better to make a 24cm long windings with 0.2mm wire on a 75m pvc pipe? I plan on using a full bridge with parallel 40n60n igbts. Also i wanted to ask is my topload ok, i made it myself from some copper pipe. Any later questions i have i will make in this post.
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Hi Miki and welcome to HVF :)
It is great to see young people taking on the challenge of building a DRSSTC.
I calculated your tesla coil resonant frequency (https://kaizerpowerelectronics.dk/calculators/helical-coil-calculator/) and you have around 1300 turns and which your topload you are properly around 130'ish kHz resonant frequency, looking at the tesla coil impedance list (https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/secondary-coil/), you properly have a impedance higher than 60k, so you should be designing for a high impedance inverter. This means lower peak current, longer on-time and that means you should have more turns on the primary coil and a smaller MMC in order to hit high impedance in the primary circuit (https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/). You should also check out the MMC calculator to make it easier to get it right in your Tesla coil. (https://kaizerpowerelectronics.dk/calculators/mmc-calculator/)
What are you planning to use as driver? There is a great variety of the old school universal driver 1.3b (https://kaizerpowerelectronics.dk/tesla-coils/universal-driver-1-3b/) and up to the latest fully digital and PC controlled NextGen UD3 (https://highvoltageforum.net/index.php?topic=188.0)
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I am planing on using ud2.7. I have used this coil before with a smaller topload and 16 turns primary. I was afraid with this bigger topload it would arc back to primary. This is the video of it on 300vdc. It sadly died shortly after. I think a biggest problem was phase lead as i have been using a pll circuit also long wires from bridge to primary, no snubber capacitors.
Few other questions.
1.How long sparks should i expect?
3.Should i make a primary with tap points or go with a primary simular to one shown in my video?
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Your primary looks fine. With it being fixed inductance, you will need some way to add and/or remove capacitance of the MMC between H-Bridge and primary coil. That is my preference - adjusting MMC rather than primary winding. However, tapped primary winding is much more common. (Ferrites can be used to adjust primary frequency, but there are many complications to consider for that option.)
Arc length depends on many factors, especially enable pulse width and repetition frequency. I've had best success with high (1kHz+) repetition with ramped pulse width.
For H-Bridge layout, I recommend copper planes as in this post:
https://highvoltageforum.net/index.php?topic=1324.0
Good luck! Nice progress already!
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I am using a layout of loneoceans easybridge. Soon parts should arrive so i will post when i find new problem or finish it. Adjusting a mmc wont really be problem as i am using 50 capacitors(2kv 4.7nf). Thank for the help.
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So a little problem has risen. I used non inverting mosfet driver UCC27424 instead of UCC27423. Will making a mod board that fits on phase control and inverts the inputs be good enough until i order replacements.
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Yes, inverters on those two 74HC08 outputs should work fine. The inverters will add a bit more delay, so require slightly more phase lead to compensate.
Another option is to change the 74HC08 to a 74HC00 (AND to NAND gate). If you do that, bypass the inverter on pin 8 of the NAND gate to keep enable logic correct (bypass 74HC14 pins 12 and 13).
For your previous concern about arcs to the primary coil, most DRSSTC designs include a strike rail near the top of the primary coil. That's a grounded not-quite-complete turn of exposed conductor (ie. copper pipe or ...) with diameter a bit larger than outside of primary. Any arcs that head down will hit that rail before reaching the primary.
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Finally made the mod board work :D. Turns out my first ic was broken. It isn't tuned right. Primary side is 150kHz and secondary is 185kHz with no arcs. No phase lead is set jet. I had issues with it arcing back to primary but lowering the primary fixed it. Later I might change to pancake primary.
So here is a video of it working:
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Congratulations!
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I need to ask some questions.
On what amperage should I put ocd for my 2 parallel 40n60n igbt full bridge?
What is easiest way to see if I am not too far away from zero point switching? I don't have a differential probe and I only have usb oscilloscope.
Soon i will upload another video.
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What is the full part number for "40n60n"? I'd need to see a datasheet in order to estimate current capability. Also, what gate voltage are you running (in other words, what supply voltage is running to the UD2.7 board)?
Do you have a scope probe capable of measuring 340V waveforms even if not isolated? If so, you can capture useful H-Bridge output waveforms even on top of the line-frequency base. Of course, DO NOT CONNECT THE SCOPE PROBE GROUND TO THE H-BRIDGE BUS SUPPLY. (However, response will improve if the scope ground is wired through a ~0.1uF 400+V capacitor to H-Bridge VBus- rail.) Trigger on the H-Bridge output waveform, adjusting trigger threshold for the lowest (most negative) voltage that captures waveforms. You will be capturing waveforms once per line cycle, enough to be useful. When voltage phase is lagging current, the H-Bridge output will show a larger noise spike at switching (caused by IGBT diode reverse-recovery snap-off). At zero-phase there is sometimes a triple-transition on H-Bridge outputs - rising,falling,rising in rapid succession instead of a clean rising edge. Slightly more phase lead (ideal point) and H-Bridge outputs will transition cleanly and smoothly.
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What is the full part number for "40n60n"?
Full number is 40n60npfd.
Also, what gate voltage are you running (in other words, what supply voltage is running to the UD2.7 board)?
I am running 20v.
Do you have a scope probe capable of measuring 340V waveforms even if not isolated?
I have 10x probe rated at 600v CAT II but I think my scope is made for max 6v with 1x probe so answer is I cant measure 340v. I haven't tested my coil at 300v yet max i have gone to is 120v.
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I've found data for an IGBT part SGT40N60NPFDPN. I'm guessing that is what you have. It is rated for 120A peak, 40A at 100C case, 80A at 25C case temperature. My rule-of-thumb is that IGBTs fry around 2x rated peak current or 4x rated average current in DRSSTC use. That would be about 240A per IGBT, 480A for a pair IF they share current perfectly evenly. That is destruction current, so you want OCD a ways below that, perhaps 300A. I'd start even lower, ~200A until you have phase lead dialed in. Others here may have more experience with similar parts.
Sometimes there is enough switching glitch showing up when probing driver output (GDT input) to use for phase lead adjustment. It is hard to predict exactly what you will see there. Another option is to form a couple turns (loops) of wire from scope probe tip to ground lead. Tape over the wire ends (over the probe tip and ground clip) to avoid bumping any high-voltage nodes. Use this as a magnetic-field probe around the IGBTs or VBus leads to the bridge. That will often pick up enough signal to see the switching edges. You will need to experiment with loop size and placement to get clear pulses (or at least spikes and ring-down) at switching times.
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Long time no update.
I tested it at 30v and this is what i get:
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It looks bad. I added a small inductor and forgot to place a jumper so now some resistors burned and I suspect comparator is dead. I haven't yet replaced it.
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Yes, UD2.7 has the issue that a missing SV1 jumper can fry downstream parts. Such mistakes are frustrating, but part of learning. I've made plenty of such mistakes over the decades.
The scope plot shows 5V/division. Is that really 50V/div using a 10x probe? Are you scoping from one H-Bridge output to the other? If so, grounding one side of the H-Bridge through the scope is not good practice even if the H-Bridge power supply is isolated. There is often enough capacitance from supply to ground to cause problems. Connect the scope ground to VBus- (negative H-Bridge power input), then scope one or the other H-Bridge output. (Of course, do not connect the scope ground to VBus- if VBus- is not either isolated or grounded through the power supply.)
Hope repairs go well!
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I scoped from Bus- to one output but got waveform looking like a sine wave. Switching to the other output I got waveform attached in my last post. I will have to get a adjustable inductor soon.
After replacing passive components it seams that comparator died.
But for now I have more important things to do.
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Is this good? I dont have a adjustable inductor so this is the best i did:
First with no inductor:
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With inductor
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Max sample rate of my usb oscilloscope is 48MSa/s.
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What circuit node are you probing? If this is one of the H-Bridge outputs, it shouldn't be going below ground. Both H-Bridge outputs should switch from ground (VBus-) to VBus+. Is there offset in your scope? If you probe VBus- and then VBus+, do you see the correct DC voltages with your scope? It should display a flat line at 0V for VBus- (with scope probe grounded to VBus-). It should display a flat line at 15V or whatever voltage you are feeding to VBus+ when probing that.
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Seems like i forgot to put probe ground to Bus-. But i cant test anymore tonight so i will do it properly tomarrow. And another thing is that i get arcing to primary. Seems like i will have to make a pancake primary. Still testing at 120v and not putting it mains (220vac) rectified.
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Of course, don't connect scope probe go VBus- when mains-powered!
Were you running 15V for the scope test? The scope is showing about 15V waveform. The second (with-inductor) waveform looks clean towards the later (right) side. Perhaps current is ramping up across that capture. It is handy to capture current on the second scope channel if that is possible. Either probe across the 51ohm feedback input resistor or add another current transformer for scoping. If scoping the 51ohm feedback resistor, scope just the resistor even when an inductor is added in series. That way the scope trace matches current phase, not the lead-compensated version.
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Long time no update :D I have done some tests and this is a photo of a breakout on 120vdc. It is 10-15cm long. It works on 120w and everything is cold to the touch(except primary that gets a little warm)
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Nice picture! And congratulations on your progress.
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I tested it on 300 vdc and my not really good secondary design finally met it's limits But not all is lost. I got a topload higher and it is pretty badly done but now. Have no flashovers.
And then I asked what song to play on it and I now needed to test it on higher notes.
Sorry for grammar and misspelled words I am in a hurry
Edit: Links are fixed now
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Great results :) There is however no sound on your first two videos?
The problems with flash-over in the first video is "racing sparks" due to too high coupling between primary and secondary coil.
It is interesting that it did help to raise the topload, the field lines from the topload could be too close and fight the voltage distribution on the secondary coil? DaveKni? Uspring?
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I can only speculate on details. Here are my thoughts:
Noticed that both racing sparks occurred just after a ground arc rose and stretched enough to break. Perhaps that breaking-arc situation is causing momentarily-higher primary current or less-even electric field distribution up the secondary.
Two possibilities to why raising top-load helped: First, the initial top-load position is roughly at the top of the secondary, making a shorted turn. Raising the top-load will increase secondary inductance and lower coupling a bit. Second, it may be a bit out-of-tune after the change. Seems like performance was reduced a bit with the raised top-load.
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There is however no sound on your first two videos?
Video was taken using a "slow motion" mode on my phone( only 4x slower) so there is no audio.
To me it seems to start from the topload as is seen from another angle.
I can say that performance was reduced a little after raising the topload.
Should I wind a new secondary taller then this one but with ticker wire to try to keep resonant frequency the same.
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Thank you for the new viewing angle! That looks more like an issue with top-load smoothness rather than "racing sparks". Raising the top load will help with that. Or, you could keep the top-load at its lower position and make it smoother. Add another ring or two to improve the toroid approximation (more closely-spaced rings). Make sure all ring mounting is all internal with no protrusions, at least no protrusions on the bottom side.
Also, a second grounded strike ring at the bottom, larger diameter at the same height, will reduce peak field, reducing the chance of an arc starting at the ground strike rings.
I expect secondary frequency is slightly lower with the raised top-load. At its higher position it blocks less magnetic field from the secondary. No need to rewind the secondary. Instead lower primary frequency a bit to match. Add another turn (or fraction of a turn) to the primary winding or increase MMC capacitance a little.
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So after some testing I noticed that it was sparking inside a tube I used to get topload higher. After replacing tube with another cylinder it was sparking from end of the secondary to the ground around primary. To me it was odd that placing a single turn of electrical tape stopped sparking. Performance has improved. I don't have a video to show. I will order some wire for a new secondary as this one has one place I needed to solder after a accidental drop. I will make it taller and try keep resonant frequency the same according to javatc. Wire should arrive by mid April in worst case.
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Electrical tape cannot block the entire Tesla coil field, but it can redistribute local fields enough to prevent arc initiation there. Corona at the high-field point under the tape is likely to eventually degrade tape, with arcs eventually forming there again.
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Wire came from UK and i made a new secundary. Now topload looks too small. But no more flash overs and with new primary it has a lot better arcs. This is me next to it. And i will add a video after i record it.
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Good job! I can't believe you did this all by yourself :D
Svaka čast da si sa 14 godina uspio dovršiti tako kompliciran projekt, za bilokakvu pomoć stojimo na raspolaganju :)
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Well i made it with my twin brother and it is 15 years old (my birthday was 15th april).
Not a valid youtube URL
Youtube shorts dont seem to work with this so here is a link directly:
https://youtube.com/shorts/iLdY4g5vxb4?feature=share
It isnt the best but i am happy with it. This is a half way in between C3 and C4 note in midi editor.
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Update time!
I have to make a new topload. When a arc hits ground i placed there my usb to midi converter crashes and stops giving new notes. A better video will be uploaded tomarrow.
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So i come with a problem. After a flashover to primary performance is bad. Current stops rising as it can be seen:
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I don't know what is happening so I am asking for help from people more experienced than me.
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It would be much easier to answer with information. Scope traces have no vertical scale listed, nor which signals are being probed. (I'm going to guess that the cyan trace is one H-Bridge output and yellow is primary current. No idea on scaling.) Also, no info on setup. Bridge supply voltage? Secondary in place or not? Other load instead of secondary?
Guessing on everything, my thought would be a shorted turn on the secondary where the strike hit.
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I am sorry for not providing information and also for asking this question before trying to replace igbts. I only ever got igbts to fail by short circuiting so i thought they were still alive. Now it works.
Thanks for your time. Next time i will prepare the question better and i will provide all the information.
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Don't worry. You are learning a lesson that will help with college (and even hi-school) science classes. Students frequently give answers without units, and that reduces grades. You have a head-start on your future science and engineering studies: Include units with measurements and calculated values. And, lab reports should include a description of the experimental conditions, such as the grams of reactants used in a chemistry experiment.