120VAC Mains Ramped Builds

[Magneticitist]

Got a lot of useful information reading this website so for what it's worth here are some pics and a little info about a ramped build I thought worked out pretty good. ZakW posted a lot more info about a similar build which has gotten great results. I'll probably try to rebuild mine and jack it all up so here is the breakdown.

I saw good results from the Loneoceans RSSTC and one shown on SciTubeHD's youtube channel so I basically tried to wind some coils with similar dimensions and resonant frequency. I also tried some other staccato interrupters already out there but Gao's seemed to work the best for me. I've found it difficult to exceed 12 inch arcs on an SSTC without upping the coil size so the budget QCW mains ramped approach seems like a really good setup and who doesn't like sword sparks.

They are based on Steve Ward's SSTC 5 driver (https://www.stevehv.4hv.org/SSTC5/miniSSTCfnlsch.JPG) with a "staccato interrupter" in place of Steve's 555. I'm running FGA60N65SMD IGBT's on it and still using a 1:1 GDT but using a 15v regulator to power the gate drivers and this just makes things simpler.
Other changes are things like the DC blocking capacitor value at the driver outputs (which should probably be experimental, I think I have like a 2uF ceramic) and the addition of a 1uF DC blocking capacitor in series with the primary (a few .33uF 1200V MKP caps I had).
I had a fairly large T37 core so I used that to wind a single GDT for driving both halves of the bridge. It allowed me to fairly easily wind 5 twisted wires. I have a CT for the feedback with about 30 turns. To add PLL feedback I put a 5v driven CD4046 in between the hex inverter and the gate drivers.

Below are the two builds I've tried with the half bridge on the left and full bridge on the right. They are both using very similar coil dimensions of 36 AWG on 9cm tall by 8cm wide formers (and run about 400khz). A 32 AWG coil of slightly larger dimensions seemed to work well also. The one on the left has the staccato and logic transformer inside the box and the one on the right currently uses an external logic supply and gets the mains sync from a transformer inside my interrupter box. I plan to get a nice toroid for the full bridge and hopefully hit that 20 inches. They are both more or less identical builds but with one using the full bridge and PLL feedback.


This is is a big universal interrupter box I went ham with trying to put everything I could into it over time. The interrupter circuit is isolated from the RCA plug with an optocoupler and 9v battery which I found almost necessary without 'getting lucky' dodging interference. I did the mains sync like that because I figured I'd want to be able to run any other builds I make mains synced without having to make a new circuit each time. I'm using Gao Guangyan's circuit seen here https://www.loneoceans.com/labs/sstc3/schema_sstc3_staccato.jpg but with C4 modified for the full 60hz half wave (quieter thicker arcs due to adding and shutting off after the downward slope).


Bridge and driver board. I believe there is about 2uF worth of film caps across the bridge and I stacked what I had at the time.
There are 15v, 12v, and 5v regulators, the 12v just being for the fan. There is a janky heatsink I used which was just a couple alu plates from somewhere I put together so it has this fan on a 40C N.O. switch. At ~8ms and highest BPS it appears to pull around 5A from the wall with the current tuning. I noticed the arcs were decent enough without the PLL though.


Using the two UCC2732x gate drivers which seem to run the full bridge ok in this operation but it's possible at ~8ms on times at highest BPS they will start overheating eventually. If I run it hard for a while to the point I can feel the heatsink getting more than just warm (with fan blowing) then the output seems to drop a little probably indicating the drivers and switches don't like it. Nothing gets too warm at the lower break rates it typically runs so it all kind of works out. I get them from mouser and Ebay/Amazon or something like that will always give you fake ones so don't do it.


A pretty basic layout that hasn't punished me for it but hey I'm not recommending a slack build or anything. This is the 2nd time I made a full bridge "test layout" like that I ended up just keeping in a final build, the other being a DRSSTC which uses the same kind of bridge layout, but to be fair might be getting saved by the snubber. I usually test with an isolated DC supply first, then low voltage AC, then full mains. So far with various coil testing these IGBT's have held up so they are pretty trusty.


A few shots of some ~18 inch arcs. I have a piece of foil above set to 20 inches from the breakout point which I could not get it to strike no matter how clever my insults were. When I had it set to 18 inches it would strike it every now and then but who knows what slight variations could result given environmental changes etc. I was originally struggling to get it to hit 16 inches before just messing with the primary a little bit and randomly testing various phase angle adjustments.




Here's a 16 inch strike from the half bridge catching mainly the tail end of the arc. I was pretty liberal with the size of the boards so in reality the spark to coil ratio could look much better after condensing the box down and everything looks smaller. I tuned that half bridge, got it to strike 16in, then was too excited about it to mess with it any further lol.


When it comes to the longest arcs from such a build it seems like it becomes a battle of finding a running frequency which is not too high or low, as well as trying to get it to form arc channels which don't branch on their way out as actual swords. That is to say I've seen tuning which seemed better in phase and probably had more power in the arcs but due to a tendency to branch more, a different tuning which pulled less power might yield longer discharges. I've kept fairly high coupling with these something around normal SSTC range and tried to keep the primary just out of streaking. There seems to be a certain science to 'encouraging' discharges to form just right as that voltage in the secondary starts to skyrocket. Slight changes in the breakout point length can for example make a big difference. A stuttering output with popping and clicking may indicate this energy trying to go somewhere and ending up in primary discharges you might not see in the light, where it may otherwise find its way out a longer breakout point, or one which is oriented to the side for example. I think using mosfets and an even smaller coil maybe closer to 600khz could get either the same arcs or longer. That's about all the insight I can personally offer into it so if you made it this far reading thank you for your sacrifice.

[ZakW]

Thanks for the shout out!

Awesome results! I saw your latest videos, and the 18in arcs are impressive. Best of luck hitting 20in!

Your videos have been really helpful and I find the staccato really my preferred interrupter for SSTCs. I have referenced your modified interupter a lot. The regular 555 timer interupter makes the coil so loud. Plus, synced halfwave gives longer sword arcs... seems like a win win.

I am working on modifying the interupter so it does not require a 12vac transformer, less parts to make it more simple. I will make a post soon once I can test it more. Also working on creating proper PCBs so I can rebuild my coil.

Thanks for sharing your progress and methodology, it's been very helpful. Good luck and I look forward to seeing your progress!

[Magneticitist]

No transformer would def make everything even handier. Even with it I think it's pretty nifty since one may use a transformer for powering the logic anyway so they can just reuse that one for the staccato. Overall this kind of setup does seem like a win win even for a first build but so far I haven't been able to really figure out what is most crucial to getting the longest discharges here. All I can really do is try to document exactly how I've built them and compare results with other variations.
For example I've taken some old half bridges I built and tried running them the same way with the same coils with poor results. They are old circuits I had thrown together without much care but seemed to work about average with the coils I wound for them. Similarly I tried the same coils out on an old PLL half bridge board I made which also seems to run ok on antenna feedback. Just another basic half bridge but poor results in comparison where everything runs clean but spits short arcs. On average I'd say with a half bridge build I might try staccato on, the sparks I'm looking at are going to be in the 6-8 inch region, maybe 12 inches or so if the coil is large enough.

I've gotten more comfortable with the PLL feedback though. Originally I was kind of iffy about messing with the knobs while the coil was running not wanting to blow the bridge but it seems unbothered when dialed in good enough. Seems maybe the best/easiest way to try shaping the discharges a little bit is to just run it at the max voltage then play with the phase angle. What I've noticed in some builds is there is a phase angle which detunes slightly and begins to try branching the arcs a little more the further shifted it becomes in that direction, however if only slightly adjusted the swords will retain their shape while becoming slightly longer. The VCO running also seems to just be a reliable way to ensure operation at any given time for switching into various modes.
I'd say my ideal setup would be trying to replicate the longish arcs somewhere around the 12 inch mark at 120VAC, but have it switchable between full wave/half wave/smoothed/mains synced. This would hopefully be easy enough to run reliably in all modes without a really beefy design.

What's interesting to me is when I look at the unsmoothed CW output and see those longest streamers breaking out past the "bush" I assume I'm looking at those 170VDC peaks. So if ran staccato I assume those peaks is only what I'll see. I remember on a different full bridge build the full wave rectified mains was looking pretty thick. It was about 6 inches of 'bush' with the peak streamers reaching to about a foot. This was a fairly powerful and large setup in comparison though so it was not surprising to see. I assume staccato operation of the same would result in something like the 12 inch streamers.

So when looking at a coil that is only around 4 inches tall or shorter, it's a little confusing to see output that reaches the same length or longer. It gives me the impression then that if you have 12in+ staccato arcs then from full or half wave rectified mains it should look like a big bush with streamers reaching out to 12 inches. My recent ramped setups will be overdriven in CW, but work well interrupted. Some older builds seem to work well in CW, but not so well interrupted compared to the recent ones.

At this point it doesn't seem like the PLL feedback is necessary since both of us got away without it in a build. You used mosfets and I used IGBT's so there's nothing special there. Your build likely has slight variations to mine and still seems to work about the same.. so what really are the most important factors to keep in mind?
I wish I could better try to rationalize what it would be so next time I build one I'm not just trying to copy what I did before exactly while hoping for the best.

[ZakW]

No transformer would def make everything even handier. Even with it I think it's pretty nifty since one may use a transformer for powering the logic anyway so they can just reuse that one for the staccato.

I tried using the 12VAC transformer initially to power the driver but it was unable to output enough current so I had to switch to a sperate supply. I dont have any other small AC transformers on hand and I did not want to try and source one for every build so I figured it would be nice not to need it. Plus not including it cuts down on the overall size so the final build can be more compact.

What's interesting to me is when I look at the unsmoothed CW output and see those longest streamers breaking out past the "bush" I assume I'm looking at those 170VDC peaks. So if ran staccato I assume those peaks is only what I'll see. I remember on a different full bridge build the full wave rectified mains was looking pretty thick. It was about 6 inches of 'bush' with the peak streamers reaching to about a foot. This was a fairly powerful and large setup in comparison though so it was not surprising to see. I assume staccato operation of the same would result in something like the 12 inch streamers.

So when looking at a coil that is only around 4 inches tall or shorter, it's a little confusing to see output that reaches the same length or longer. It gives me the impression then that if you have 12in+ staccato arcs then from full or half wave rectified mains it should look like a big bush with streamers reaching out to 12 inches. My recent ramped setups will be overdriven in CW, but work well interrupted. Some older builds seem to work well in CW, but not so well interrupted compared to the recent ones.

I could be wrong but my understanding for why the mains synced arcs are longer is because of how the voltage is applied to the primary. Since the voltage is ramped the initial arc starts, then grows from a single point which gets longer and thinner as it nears the top of the cycle. As for CW or full wave rectified DC, the voltage is just dumped into the primary in a short interval and immediately causes a tremendous potential to build on the secondary breakout causing a flood of arcs in all directions.

I have also heard that there is an optimal frequency range for achieving sword arcs. I dont recall the range off hand right now but I wonder if that has impacted your results when testing different bridges with different coils?

At this point it doesn't seem like the PLL feedback is necessary since both of us got away without it in a build. You used mosfets and I used IGBT's so there's nothing special there. Your build likely has slight variations to mine and still seems to work about the same.. so what really are the most important factors to keep in mind?
I wish I could better try to rationalize what it would be so next time I build one I'm not just trying to copy what I did before exactly while hoping for the best.

I read your comment on your latest video about not having good results with 460's FETs. That is pretty much all I use and have had good results, not sure what might cause that.

I kept having issues with my feedback, likely due to interference and component values. With the half bridge I was able to hit 16in arcs from a 6in secondary. The acrylic had cracked a bit so I had to cut the coil down a couple inches. It is now around 4.5in, I am looking forward to seeing how it performs.

As far as my tuning process goes, here are a few things I check and adjust to get the longest arcs: I plan on documenting this in a large post down the road in hopes that it helps others.

**these are just my observations, not facts**

- Top load height from the top of the secondary. I mount the top load to the coil using a 2in long bolt so I am able to thread it up or down to adjust the height. When it is at the lowest (closest to the top of the secondary) I get noticeably smaller arcs, by several inches. As I start to raise it the arcs get longer, until a point. Sometimes I have had to extend the breakout point a little bit with a bit of wire when the top load is raised too high.

- primary coupling, height, turn spacing, and number of turns:
     - primary coupling: I always start by directly wrapping the primary on the secondary with a few sheets of plastic or kapton tape for added insulation. If I get racing sparks or corona discharge I will use a spacer to reduce coupling. Seems to impact consistency the most. If coupling is too high the coil can skip beats.
     - height: this has a big impact on arc length. At lower voltages I will use my hand to raise the primary up and down. Starting low and going up you will find the spot that gives the best results. Passing that point leads to reduced arc length.
     - turn spacing: This combined with turn height helps a lot too. Recently, I have noticed that my last two build have always had longer arcs with spaced primary turns. Spacing the turns increases coupling while keeping a safer distance from the secondary. Spacing the primary turns and adjusting the height has helped me squeeze out as much performance as I can get.
     - # of turns: fewer turns gives me longer arcs to a point, it also causing excess heating due to higher currents. I like to be able to run my coils for long runs so it is usually a trade off for run time vs heating. In the beginning I wind a multi tapped primary and just go 1 less turn at a time until I find the best results. Once that is locked in I play with height and spacing. Too many turns reduces arc length.

Hopefully all of that was not just a repeat of things you have already tried.


In the picture of your half bridge and full bridge, have you tried swapping the top load to see if that makes a difference on the full bridge? I wondered if the thicker non-toroidal top load is robbing you of longer arcs?

[Magneticitist]

I've been grabbing Jamesco transformers since it seems difficult to source cheaper alternatives but on most all my coils I use a 15v gate drive in which case even with the full bridge I've seen only minimal current draw. I like to use a DC supply for testing and in most cases feeding a 15v 1.5A regulator with 20VDC or so I'm looking at around 100-200mA tops being pulled. This all depends on what kind of operation I'm running and if trying to run a full bridge CW I might want to beef up the gate drive. I've never done it because the two UCC drivers seem to chug along fine so far.

As for say unsmoothed half wave CW I just see the arcs as being the full ramping of the half wave upward and downward slopes with no breaks in between aside from the natural line frequency. Since staccato would just be trying to initiate a ramp at a lower break rate than 60hz I just picture it as being able to spit cleaner and possibly longer arcs. So that is to say 99% of the time I can look at the max output unsmoothed CW and see where the peaks reach out to, and assume I'll see those same peaks or maybe longer running staccato. In that regard it seems odd imagining a 4 inch coil spitting something like 12+ streamers in unsmoothed CW mode assuming it could handle it.

When it comes to 460's I wouldn't say I've had bad performance with them but I'd just prefer something more modern when possible. For example in the PLL circuit I recently got running better the 460's in there are working well and do not run warm or anything. I can't say however if they are part of the reason why I couldn't get great ramped performance from the coil they are running. The body diodes are slow to recover I believe and when you start running high power the dissipation is up there, but they do indeed get the job done as many coilers have shown. I see the 60N65's as better modern replacements when I plan on having a 500v+ ceiling and they are about the same price.

I can't say there is really an optimal frequency range for the ramps but it seems that you can notice the arcs start to become crooked and branchy once you start getting below about 300-350khz. At least 400khz or so is recommended for the straightest ones. I thought they were pleasing enough at around 230khz and still like to shoot straight upward but do indeed lose that true sword shape.

I agree that slight adjustments in the primary is a huge factor and something I seem to play a lot with on most coils. I probably wind about 10-20 different test primaries for a build after realizing such slight changes can make big differences. A single turn made a huge difference on my half bridge. So far the only commonality I seem to see is that a sweet spot is usually right on the edge of racing streaks. Often times I've brought it to that edge then just added more insulation to get rid of the streaks.
This is not something that would seem ideal if tuning for 120VAC then deciding to up to 240 as it will likely arc over.

[ZakW]

Hey Magneticitist,

You manage to make any more progress on your ramped builds? I designed a driver and mains power supply PCB that I finally got in the mail a couple weeks ago so I have been messing around with several different secondary coils. So far I cant seem to break 16.5inches at 120v.

I plan on making a more detailed post later with my complete schematic but here are a few pictures.

Here are the boards: The larger one is the driver that contains the 556, UCC27425, and HC14. The smaller board "power supply" is essentially a fuse and a single diode for halfwave rectification to power the h-bridge. The other half is the optocoupler that senses the zero crossing of the AC signal and feeds that to the interrupter.



Here is the output of the optocoupler that is then fed into the 556.



Here is the output of the 556. I can adjust a trimmer resistor to get it exactly at zero crossing






Lastly, here is a picture of a scope probe hanging near the coil.



Nice ramped shape.

When you hang a scope probe like I did above, is that the voltage or the current being represented on the scope? You mentioned in your video that the initial yellow stripe (in line with the vertical trigger) before the start of the ramp was 'hard switching'. Can you explain a bit more about that and what causes it?

Here is a picture of my 4in coil hitting 14inches. I managed to hit 16 tonight but didnt take a picture.



I am really happy with 16in from a 4in secondary, since that is 4x the length. That is not bad from just 120v!

So far the only commonality I seem to see is that a sweet spot is usually right on the edge of racing streaks. Often times I've brought it to that edge then just added more insulation to get rid of the streaks.

I have noticed this exact thing as well. Getting it on the verge of arcing to the coil gives the best results. I also noticed that spacing the primary turns out at different heights on the coil can cause the output to branch more where as warping the primary without a spaces can make straighter arcs... too many variables.

Thanks!

[Magneticitist]

Hey Zak I just happened to be free this morning browsing around and saw your post. Those are some nice boards you have there and probably the best way to do it with the dual gate driver and your ZCD circuit. I've had one of my setups sitting on a 'test table' for a while and haven't ran it but was planning on getting back into it now that I'm back in town with some free time. I remember getting the full bridge to spit 18 in arcs with a specific tuning but honestly after playing with it again some time later the arcs seemed to decrease in length again. I'm not sure if this was the result of just me messing with the potentiometers or what. At the time I tried to remember the way I tuned the phase angle by how hard it was switching at the lower voltages. That's what I meant by it was hard switching in the beginning, normally with how I see them running they will pull some decent amps at the lower voltage and I can feel some hard knocking in the variac, but when reaching full line voltage that knocking goes away and that current draw sort of 'levels out'. That is to say it just seems like the phase shift going on is causing it to lose some throughput. I noticed that by tuning it so at the lower voltages that hard 'knocking' was softened out a bit I had basically detuned the coil to have it get closer in tune at the higher voltages. I noticed that initial spike in the waveform would shrink slightly, and just about the point where I would feel the knocking go away was a sweet spot and any further detuning would start making the waveform funky. But yea I'm just looking at the voltage waveform to free air with my hanging probe. I've measured the DC blocking cap before but found free air voltage to be a good enough indicator.

So when I run no PLL and use the HC14 by itself I usually see this kind of operation where it seems to be switching fairly hard at low voltage. I crank the variac knob to 120VAC and all that goes away, but at the same time I feel like I've shifted the phase relation a bit at max voltage. So recently when tuning the PLL I tried to adjust it to account for this by making it so it has the best output at the max voltage and a fairly weak output at the lower voltages.

It's a little similar to tuning a DRSSTC for streamer length to some degree I think. I move my hand closer to the coil I see the output increase so it seems more accommodating to long streamers. Or it could be tuned the other way around where it has the best apparent output until I bring my hand close. I've found I needed to finely tune this in order to run a CW setup max voltage like that from the wall to keep it from pushing over 10-15A.

I still have some more coils to finish winding for the all ramped setups but I got the impression about 16 inches or so was going to be the consistent max I could reach at 120 but this has been the case for both the half and full bridges. Getting the full bridge to hit 18 again just seems like a pain. I was supposed to drive that with 240 so I still need to see how that goes.. was going to try some 60VAC transformer I had in reverse just for kicks. If something like that works for longer streamers I think it would be pretty awesome to still have everything in one 120VAC plug.

[ZakW]

Hey, glad you saw the reply!

Those are some nice boards you have there and probably the best way to do it with the dual gate driver and your ZCD circuit.

Thanks! They are only the second PCBs I have had made. I made a couple mistakes (solder mask and component values) but they are working great so far. I am really pleased with the optocoupler performance, it has been really consistent. Forgot to show the h-bridge too! I might consolidate the h-bridge onto a single PCB with the driver and power supply in the next iteration. It is nice having it separate for now.
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So when I run no PLL and use the HC14 by itself I usually see this kind of operation where it seems to be switching fairly hard at low voltage. I crank the variac knob to 120VAC and all that goes away, but at the same time I feel like I've shifted the phase relation a bit at max voltage. So recently when tuning the PLL I tried to adjust it to account for this by making it so it has the best output at the max voltage and a fairly weak output at the lower voltages.

Here is a picture of the output of the UCC. You can see it is on for a period in the beginning and then off, then on again. I am not sure what is causing that short initial on time - which I assume is that small spike in the secondary voltage waveform above (yellow). I added an additional bypass cap of .47uf which seemed to lessen some high frequency switching of around 2.3mHz, but that gap remains. 

It's a little similar to tuning a DRSSTC for streamer length to some degree I think. I move my hand closer to the coil I see the output increase so it seems more accommodating to long streamers. Or it could be tuned the other way around where it has the best apparent output until I bring my hand close.

I experience this as well. Usually only when the primary is too low on the secondary. Once I move it up or add spacing to the turns I get that nice quiet arc thud sound.

I still have some more coils to finish winding for the all ramped setups but I got the impression about 16 inches or so was going to be the consistent max I could reach at 120 but this has been the case for both the half and full bridges. Getting the full bridge to hit 18 again just seems like a pain.

I am getting 16in with a 4in coil with 38awg and 16.5in with a 5in coil with 32awg.

Both work best with very small toploads, like just a small disc. That keeps the Fres around 420-400kHz and helps the arcs to go straight. Larger toploads make the arcs branch out only with a few being straight.

Your coils seem to have large toploads. Is 400kHz your loaded Fres?

I was supposed to drive that with 240 so I still need to see how that goes.. was going to try some 60VAC transformer I had in reverse just for kicks. If something like that works for longer streamers I think it would be pretty awesome to still have everything in one 120VAC plug.

I would likely have the same issues at higher voltages, especially 240v. I was simulating and kicking around the idea of a half wave voltage doubler. Something like this http://www.electricalbasicprojects.com/wp-content/uploads/2017/11/Voltage_Multiplier_Circuit.jpg

Even if it was not fully doubling the mains voltage, getting a bigger ramp would still be great and it only takes a few components. I have yet to really look into it more though. Do you think that could work?

[Magneticitist]

I had assumed that initial little spike was the capacitors discharging though I'm not sure on that. Maybe the caps are cycling a small feedback loop started by the rising edge of the interrupter and the cap discharges and kills the loop before the actual line voltage starts to rise enough to get it going again. I suppose a doubler could work but I don't think the ramp will be preserved well enough and the sparks would get branchy. I've gotten some decent little ramped swords off straight DC setups though so it's hard to say. Playing around earlier I was able to adjust a phase angle to where I got some nice branchy arcs that seemed more SSTC-like or even small DRSSTC-like with high on times and just tuning the knob again brought the swords back. I'm using 36awg again and the coil runs about 400khz yea. I need a nice little toroid but a properly sized one did make a difference. In my first half bridge setup I had a bootleg cylinder topload and by tuning the primary a little and adding a nice toroid which was a little smaller instead that was what improved the output to 16 inches. I have that same bootleg cylinder topload on my fullbridge so I need to replace it with a toroid like the other one.

[davekni]

Forgot to show the h-bridge too! I might consolidate the h-bridge onto a single PCB with the driver and power supply in the next iteration. It is nice having it separate for now.

Great low-parasitic-inductance half-bridge construction!  I've added a link to it in my tutorial thread, presuming you don't mind.

Even if it was not fully doubling the mains voltage, getting a bigger ramp would still be great and it only takes a few components. I have yet to really look into it more though. Do you think that could work?

I suppose a doubler could work but I don't think the ramp will be preserved well enough and the sparks would get branchy.

Ramp shape would certainly change.  Voltage would be theoretically 170*(1 + sin(t)) for t from -90 degrees to +90 degrees rather than just 170*sin(t) from 0 to 90 degrees.  Doubler start will be slower (slope of 0 initially) compared to normal half-wave-rectified.  Total ramp time is twice as long, which might be too much time to avoid branch starts.  Sounds like a great experiment!

[ZakW]

I had assumed that initial little spike was the capacitors discharging though I'm not sure on that. Maybe the caps are cycling a small feedback loop started by the rising edge of the interrupter and the cap discharges and kills the loop before the actual line voltage starts to rise enough to get it going again

If that is the case, that doesn't sound like it is causing any issues then.

I suppose a doubler could work but I don't think the ramp will be preserved well enough and the sparks would get branchy. I've gotten some decent little ramped swords off straight DC setups though so it's hard to say.

Ramp shape would certainly change.  Voltage would be theoretically 170*(1 + sin(t)) for t from -90 degrees to +90 degrees rather than just 170*sin(t) from 0 to 90 degrees.  Doubler start will be slower (slope of 0 initially) compared to normal half-wave-rectified.  Total ramp time is twice as long, which might be too much time to avoid branch starts.  Sounds like a great experiment!

I will give it a try and see what happens!

Great low-parasitic-inductance half-bridge construction!  I've added a link to it in my tutorial thread, presuming you don't mind.

Hey Dave, thanks! I don't mind at all. I try and take a lot of pictures of my build progress on my projects so I have more photos of the layout at different stages if that would be helpful. For this version I decided to use a one side copper clad board and add copper tape to the other side. That way it is more heat resistant when soldering and has added stiffness. The copper tape as you know is easier to cut and shape vs the copper side of the PCB. I figured to copper tape side could always be replaced if the solder joints start to peel up from replacing MOSFETs.

[davekni]

Hey Dave, thanks! I don't mind at all. I try and take a lot of pictures of my build progress on my projects so I have more photos of the layout at different stages if that would be helpful. For this version I decided to use a one side copper clad board and add copper tape to the other side. That way it is more heat resistant when soldering and has added stiffness. The copper tape as you know is easier to cut and shape vs the copper side of the PCB. I figured to copper tape side could always be replaced if the solder joints start to peel up from replacing MOSFETs.

Thank you for the clarification about one-sided copper clad.  I've had a harder time finding one-sided than the more common two-sided.  So I've always either used copper clad for both sides or neither (copper tape on both sides).

I think the two pictures you already shared are sufficient.  Looks surprisingly similar to my tutorial build, except that yous looks more precisely cut.  Thank you for allowing a link here from my thread.

[ZakW]

I think the two pictures you already shared are sufficient.  Looks surprisingly similar to my tutorial build, except that yous looks more precisely cut.  Thank you for allowing a link here from my thread

Of course, thanks for creating the tutorial and sharing it with everyone!


In the name of science and natural born curiosity I wound a 45awg secondary. Which is a record for me. I am not sure if I have seen a coil with that thin of a gauge.

It was originally 3 inches long on a 1.8in pvc pipe but a flash over broke a winding. After cutting off what was above the break and wrapping it in several layers of kapton tape I was left with a 1.75in secondary. ~550 turns per inch with 45awg.


I was able to get a 13in arc! Which is 7.4x the length of the seconday winding. 12.5in was a lot more consistent.

Here is the 13in arc. Ignore the scale in the background. I measured from the tip of the breakout to the number 10 marking where my hand was. Camera angle makes it look a bit off.



Here is when it broke. 32awg wire for reference.


With only a washer for the top load it was running around 417kHz loaded.

I uploaded this from mobile and had some issues. Not sure why the photos are sideways

[Uspring]

Very cool little coil  A wonderful example of miniaturisation. I hadn't thought it possible to wind a coil with such a spider web wire.

[ZakW]

Very cool little coil  A wonderful example of miniaturisation. I hadn't thought it possible to wind a coil with such a spider web wire.

Thanks, Uspring! I did not think it was either but I managed just fine using my typical method of using a cordless drill to turn the coil. It just took a bit longer. The slightest tension would snap the wire.

I am surprised by the performance given the high resistance of the secondary. The coil felt warm after ~10min of testing. Javatc also approximated the Q around 26 with the reactance at resonance being well above the magic 50komh mark. I think it was somewhere around 98kohm.

@Magneticitist

Do you already have your new secondary form picked out? I am curious with what size you are going for. So far I have tried a lot of different diameters with different wire gauges. From an arc length to secondary size the 45 awg coil takes the cake. My biggest secondary at 3.75in diameter by 5in tall with 32 awg produced the longest arcs at 16.5in.

It seems like I got the straightest arcs with the small coil when the loaded Fres was ~415kHz. Getting into ~350-380kHz range with an added topload caused the arcs to fork most of the time.

Also going well beyond 420kHz mark caused lots of branching and downward curving arcs. I made a 4in coil that was in the 750kHz range when loaded and the arcs were not straight at all.

[Magneticitist]

I've already wound a coil closer to 700khz for testing but planned on just winding a near identical coil to my first one. It's going to be about 3in x 3.5in using 36 AWG but I've been sort of slacking thinking about finding a perfect pairing of PVC pipes for insulation. For me 36 is about the smallest I can deal with winding and it seems to hold up well enough at high power. There's no way I could wind 45 so that's feat to say the least. The fact that you did it using a drill is actually really impressive lol. I go smaller than 40 I snap the wire every time and I have to do it by hand. I've got maybe one or two tiny coils using it but that baby hair thin wire can indeed throw some nice arcs.
I want to eventually do it the other way around and try coils with higher Q factor since swapping a 36 awg coil with a 32 awg coil of nearly the same dimensions got similar output. Maybe something like 32awg but with less than 400 turns. Over a foot with 45 and it being over 7x longer than the secondary is really close to expected QCW operation though so that's pretty awesome. If it can be condensed down that tiny it seems the best way to go. I think I'd have to search for prewound coils to buy for that though. With that small of a coil, no transformer, and some neat boards it seems like the whole thing could end up looking super tiny.

[ZakW]

It's going to be about 3in x 3.5in using 36 AWG but I've been sort of slacking thinking about finding a perfect pairing of PVC pipes for insulation

That sounds like a good coil size - compact yet high turn count. I had the same issue with finding a spacer for my primary coil. If I found one but it was not spaced out enough it just caused arcs to the secondary. I had the idea to use some sort of hard plastic roll. Thankfully I had a roll of 'wire shelf liner' it is a hard plastic that looks and feels like HDPE or something similar.

I cut a chunk off on my table saw and can easily adjust the inner diameter with a slight turn. Just by making a slight change can cause the form to grow or shrink by a lot. That has allowed me to dial in the distance and back off a little when it starts arcing over.

Here is the form on a few coils.

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I also save a lot of wire by making it slightly longer than I need, that way I can just undue a few twists to allow for more slack so the form can expand then I am ready to test again. It makes adjustments really quick and easy.

There's no way I could wind 45 so that's feat to say the least. The fact that you did it using a drill is actually really impressive lol. I go smaller than 40 I snap the wire every time and I have to do it by hand. I've got maybe one or two tiny coils using it but that baby hair thin wire can indeed throw some nice arcs.

Haha thanks, the first try I got like 4 turns in and it just snapped. I realized I had to basically let it slide between my fingers just enough to guide it. Half the time I could not even see the dang thing. I ordered some 41awg wire so I dont have to go through that again.

The coil above is the 3.75in diameter with a 5in secondary using 32awg.
Per JavaTC:
Fres - 510kHz
Secondary Q - 149
Reactance at resonance - 52kohm

with that I seemed to max out at 16.5, which is the longest I have gotten but from a specification standpoint it is on the other end of the spectrum compared to the 45awg coil. Yet performance is comparable.

[alan sailer]

The idea of using a roll of thinner plastic to make an artificial coil form is really good. I have spent far too much money buying Lexan tubing for various coils.

It would have never occurred to me.

Thanks.

[Magneticitist]

Yea the plastic roll is a solid idea I might have to try that. I've been using something I had a roll of someone gave me a while ago and it's some kind of rubbery trim but it's pretty thick so I don't have a lot of variation in the spacing. I also just ran out of it. I bet that shelf liner stuff might also be good for insulating diy foil caps.
And I agree that these tubes even the acrylic or pvc pipes are just too expensive and I can't just go to the hardware store and get any specific size of some cheap stuff I want so trusty brand of plastic roll I can cut down and form to size sounds real practical. It's funny how hard it seems to beat the streaking sometimes because apparently there is all this expensive stuff you can buy that is supposed to resist extremely high voltages but it's like it only really does it if you're super liberal with it, almost to the point where a cheap substitute is going to noticeably get the job done about the same. I remember I spent the money on some super high voltage insulating tape and went nuts wrapping a secondary with it thinking it would be some super layer of protection, but I saw no difference between it and just using electrical tape.