Post by: oneKone on March 26, 2018, 04:13:08 AM
110mm diameter, 440mm winding length, 0.3mm wire, 1460 turns. As for the bridge I was thinking about a full bridge of 82N120. Eric Goodchild wrote that 82N120 can run at the same frequency as the ixgn60n60. I'm thinking of using the 82n120 so I can go up to 600v bus.
Or
160 diameter, 640mm winding length, 0.3mm wire, 2130 turns.
With a fullbridge of cm300du-24.
As for the driver I'm on the fence to go with a 1.3b or an 2.7c driver, especially because I have an unpopulated 2.7c board, or if there's a point when phase shift should be added to a coil, at what point it's necessary. I'm hoping someone could maybe provide some insight with these more larger coils.
Post by: Mads Barnkob on March 26, 2018, 09:45:09 AM
I would advise you on building the larger CM300 coil, simply because it is a different beast of a inverter than the TO- package parts you have been using so far. It can take so much more abuse just from the shear size of the silicon die.
Both 1.3 and 2.x with phase lead will work great on your coil. Phase lead is used to minimize hard switching current when we are not hitting ZCS spot on, so as long as you can manage the extra temperature rise, there is nothing wrong with a little hard switching, but if you start pushing things to the limit and beyond it suddenly gets critical! If you run your CM300 at some 600-800A there should be no problems without phase lead, but if you want to push them above 1kA, you better well use it :)
You could always do the math according to the temperature calculations in my IGBT selection guide and see how much phase shift you can allow and still stay below 30 degree Celsius temperature rise per pulse (and be able to cool that off before next pulse).
Post by: oneKone on March 26, 2018, 12:45:27 PM
Post by: oneKone on April 16, 2018, 05:23:22 AM
Post by: Mads Barnkob on April 17, 2018, 03:06:07 PM
It is only a problem if you end up with a coil that only makes topload to strike ring sparks, but with a good long break out point that is properly not an issue.
Post by: oneKone on April 17, 2018, 03:31:42 PM
A large portion of my decision to change the secondary length was because i don't have enough wire, but i'm going to have to order more anyways to build a new pll sstc. So the big build is back on! realistically it's only about $130 price difference. Another thing that i'm thinking of changing is rather than going for cm300du-24 bricks i might go for the cm300du-12. part of me wants to try the Chinese bricks to see how far i can get, even though the sting of those ixgn60n60 still feels fresh!
I think this build will take a while. with bigger ticket items it's going to put put more of a strain on my project/hobby budget.
Post by: oneKone on May 08, 2018, 02:37:46 PM
I've ordered 3 used cm300dy-24 bricks (thank you Mads for the link) and i wound the secondary. In the past i've been winding secondaries by hand and this has proven to be very time consuming. This time it was different! i held the form between centres and used a rotary buffer connected to a variac for speed adjustment. the coil took about an hour and a half to wind.
I've applied 5 coats of polyurethane and will apply about 5-8 coats (with sanding) of oil based polyurethane to get a nice finish and shine.
the coil sitting next to the mini drsstc:
Post by: oneKone on May 15, 2018, 10:13:50 AM
I've received the cm300 bricks.... man they're big! I'm also just going to get a spun aluminium toroid, its kinda expensive but they look incredible. hopefully this weekend i'll get the driver assembled and tested.
Post by: Mads Barnkob on May 16, 2018, 10:16:17 AM
Big is good! Almost impossible to destroy with that amount of silicon on a huge copper heat sink.
Post by: oneKone on May 16, 2018, 03:48:06 PM
My guess a the moment is about 1.2m. I'm still unsure if I'm going to go with air or liquid cooling. With air I could find some heatsinks on eBay or get some vapour chamber type CPU coolers, with water I was just going to go with 2 x140mm aio.
I'm unsure if I should buy the toroid first or buy the bus and tank capacitors and other parts to build the base.
Post by: Mads Barnkob on May 17, 2018, 10:49:04 AM
Get the bus and tank capacitors first, there you have much more work to do and surprises to get, parts missing etc. A toroid is pretty much plug and play on top :)
Post by: oneKone on May 18, 2018, 02:21:17 PM
As for the heatsink I think I'm just going to turn to eBay. There's nothing local that I know of, I'm thinking of this one:
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Post by: Mads Barnkob on May 18, 2018, 02:56:13 PM
That is pretty expensive for a new and relatively small heat sink, is there no industry / scrap yard near you where you can find a scrapped variable frequency drive and scavenge the heat sink from that?
How about local HAM / radio amateurs, they usually have a good stock of heat sinks too :)
Post by: oneKone on May 19, 2018, 01:23:32 AM
Unfortunately in Perth there's not a lot around. Back in my earlier days of electronics the scrap yard would have random parts like that, these days there's almost nothing. I'll have a look at AliExpress.
This is the only suitable heatsink I have for them. They have a bit of overhang but main portion of the die is making contact.
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Post by: Mads Barnkob on May 22, 2018, 10:29:22 PM
Large enough heat sinks are however pretty expensive from new, but it did spark me to start up on a heat sink and cooling chapter for the DRSSTC design guide, as I did have some notes here and there on selecting a heat sink and some measurements from Hydron.
If it wasn't so darn expensive to ship 5 kg half around the globe, I would have sent you a heat sink from my stack :(
Post by: oneKone on May 24, 2018, 12:00:05 PM
I'm going to have to put the build on hold. i ended up cracking two teeth in my sleep, one half of one tooth was missing and the other is cracked! so now instead of buying the parts for a coil i'm going to have to save money for crowns.... such is life
Post by: oneKone on May 28, 2018, 04:52:49 AM
Assuming you could be bothered dealing with shipping a heatsink. I don't suppose you'd have a ballpark figure of what you'd want for the heatsink plus shipping?
Post by: Mads Barnkob on May 29, 2018, 07:13:27 AM
Post by: oneKone on June 16, 2018, 09:45:09 AM
I think for the mmc i'm going to use 940C20P47K-F with 3 in series and 3 in parallel, for the heatsink i'm going to go with this: https://au.rs-online.com/web/p/heatsinks/1898404/ . its a bit off putting being only 30mm fin depth but with 2 x 140mm pwm pc fans i think it will stay under control. as for the bus capacitors i think i'll be going for 2 x 4700uf 450vdc in a voltage doubler configuration.
The other day i scored 2 x cm150du-24f bricks for $30 delivered. Initial tests show them to be working perfectly, so i think for a smaller coil for my next build these will be a goto.
edit:
i was looking at these capacitors and was wondering if anyone has seen them in a drsstc before?
https://au.rs-online.com/web/p/polypropylene-film-capacitors/1235134/
Post by: Mads Barnkob on June 18, 2018, 11:13:39 AM
The heat sink will do good, noise from high air flow is not really a concern in a Tesla coil, so just give that plate plenty of air flow and the fin length will not matter, the superior cooling comes from high air flow and many fins!
DC bus capacitors sound fine, add some MKP snubbers aswell, across the IGBTs.
Neat with some smaller bricks, looking forward to drsstc4 ;)
Post by: Hydron on June 18, 2018, 12:31:42 PM
As for the snubber question, for both MMC and DC bus snubber use I have used the similar Aerovox snubber caps in a DRSSTC of a similar size (CM300s, 160mm*730mm secondary).
Mine were 2uF/1000V though, so the MMC ended up with a couple of fairly long strings to get a sensible capacitance/voltage rating. This was OK though, as I had over 50 of them available - my MMC allowed for up to 24 in series in each of 2 strings (with capacitance selected by choosing where to attach a shorting jumper on each string). This MMC works very well, and didn't seem to get warm even after a continuous 10-min run at ~1.5kW heating up a dummy load (cast iron skillet with bacon and eggs).
If you were to use the snubbers for a MMC I'd say that you'd need at least 5 in series and 2-3 strings in parallel, e.g. 6s3p for 18 caps total. Have a play with Mads' MMC calculator on his website and your expected coil parameters.
Post by: oneKone on July 03, 2018, 12:10:13 PM
In other news i've found these capacitors:
https://www.ebay.com.au/i/401383408371?chn=ps
If i'm reading that correctly that's a bargain! especially with the high ripple current described in the data sheet.
I'll hopefully be returning to this project very soon. i think i'll order the capacitors (bus) and the heatsink this friday, then the mmc capacitors in another week or so.
Edit:
The only downside I see with the capacitors I linked is the diameter. I can mount the capacitors on-top of the igbts to get the lowest possible inductance but it's more than I would like, in saying that I've seen voltage multipliers on drsstc inverters that also look high inductance that use bigger snubbers...
Post by: Mads Barnkob on July 04, 2018, 10:16:42 AM
You can actually quite precise judge a electrolytic capacitor on its physical dimensions if its made for high ripple current. The large terminals is a dead give away, but also a large diameter and short length is a clear indicator of that. Long capacitors are not good for large ripple currents as they would heat up much more near the terminals than at the bottom.
Just use some good big copper bus bars to mount them on the side of the IGBTs with a 90 degree bend or something like that. Remember that electrolytic capacitors should not be mounted upside down due to the vent hole, and you mount it on the side, see if you can possible have the vent plug/hole as much upwards as possible.
Post by: Hydron on July 04, 2018, 12:00:30 PM
As for mounting, I'd check the manufacturer recommendations - my RIFA (Kemet) caps are ok in any orientation but the manufacturer warns that if they vent then the mess will be worse if they are not facing upwards. Was not an option for me so mine are mounted downwards, and I'll just have to deal with it if they vent.
Post by: oneKone on July 05, 2018, 01:28:31 AM
I am planning to mount them vertically. I was originally going to try aluminium for my bus bars but I think I'll start looking for copper plate.
@Hydron. You're correct. Originally I was just going to run rectified mains but I thought while I'm building it I might as well go with a voltage doubler config.
Post by: Usernametaken on July 12, 2018, 10:14:41 AM
Post by: oneKone on July 14, 2018, 04:00:09 AM
i've found a couple of sellers on ebay that sell copper sheet/plate. if you search for lets say "5mm t2 copper sheet" you'll get a few hits. I'll more than likely order from ebay, just waiting on getting the capacitors first.
Post by: oneKone on July 21, 2018, 10:44:21 AM
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Post by: futurist on July 21, 2018, 05:51:07 PM
Post by: Mads Barnkob on July 22, 2018, 08:31:11 PM
Nice little stubby electrolytics by the way, for sure made for high ripple current! ...or low clearance designs :)
Post by: oneKone on July 23, 2018, 01:38:59 PM
@mads, my thinking exactly! i'm hoping the 5mm plate will stop them from moving around, if not i'll machine up some acetal standoffs.
Post by: Nijin on August 03, 2018, 10:59:08 AM
Post by: oneKone on August 07, 2018, 12:58:50 AM
Post by: oneKone on September 05, 2018, 05:44:25 AM
Ok so it's time to get back into this project! I'm going to order the MCC and snubber capacitors tomorrow night (finally). I'm going to try 3 parallel X 3 series to give 0.33uf @ 9kv.
For the toroid I've found this:
http://4hv.org/e107_plugins/forum/forum_viewtopic.php?177424.0
The concept seems easy enough to pull off, so I'm going to buy a small length of copper tube and pipe and see if I can make a few sections.
Hopefully this weekend is productive!
Post by: Mads Barnkob on September 05, 2018, 10:08:06 AM
Regarding the ringed toroid, Uspring lately made a comment about having trouble when using too think tubing, so have this in mind :) https://highvoltageforum.net/index.php?topic=457.msg2801;topicseen#new
Post by: oneKone on September 05, 2018, 12:31:49 PM
0.33 uF at 9 kV is a good compromise for a coil your size.
Regarding the ringed toroid, Uspring lately made a comment about having trouble when using too think tubing, so have this in mind :) https://highvoltageforum.net/index.php?topic=457.msg2801;topicseen#new
cheers mads,
i thought with the mmc it should be a good starting point, if i need i can always order more capacitors. Also a massive thank you for the link! in the back of my mind i knew i had seen a post on this forum, but for the life of me i could not remember. Maybe it would be worth a shot making a smaller toroid for my first drsstc and see if that gets any bad tendencies, and also how to fix them. I wonder if heavy coats of polyurethane could help?
Post by: oneKone on September 12, 2018, 12:21:48 PM
after a long ass time on the shelf i have finally populated the through hole ud2.7c designed by profdc9 -if your still lurking a massive thank you for releasing the files. I've also received the snubber and mmc capacitors. As for the heatsink for the bricks i ended up going individual heatsinks as it was half the price..
I think i'll keep the current pace of this project, for me when i start going to fast in a project/hobby it starts to feel like work or a chore, so i want to keep it fun for myself. Hopefully all this mini updates don't seem too fragmented!
anyways picture time!!!!
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Post by: profdc9 on September 16, 2018, 04:34:36 AM
BTW I put the DRSSTC PCB pack up on github
https://github.com/profdc9/DRSSTC-PCB-Pack
Enjoy,
Dan
Post by: Mads Barnkob on September 17, 2018, 11:17:23 AM
Do not feel bad about slow progress, I spent 4 years to complete my large DRSSTC. Right now I really feel the time disappearing with a house to restore and 2 kids. Just hang inthere!
Post by: oneKone on September 19, 2018, 02:28:27 AM
Cheers for the encouragement mads. You've got the nail on the head! Thankfully buying the main components is over! Just remembering all the smaller components now! I can semi relate with your current circumstances, for me it's repainting and reflooring my house... And I also decided to paint one of my car's in my garage..... Something now I wish I hadn't started! Tbh I still find it amazing you find the time to be a family man, Goto work, renovate a house, run a forum and post YouTube videos...
Post by: oneKone on February 28, 2019, 11:21:25 AM
in the time since i last posted i haven't achieved much. the bridge and the mmc are pretty much completed with some minor tweaks needed.
For the bridge i ended up using 8mm aluminium plate for the bus bars which has an added bonus of making the assembly more rigid, although i don't know if its a wise decision to be relying on the terminals of the bricks to take the load of the capacitors? As for the mmc it was pretty simple. 3mm x 15mm coper flat bar was used along with m6 cap heads to keep everything in place.
Post by: oneKone on April 10, 2019, 01:45:25 AM
Basically I had a 450x450x350mm "cube" for the base of the coil, to me that's pretty unappealing. One look I do like are round bases both a helical primary. Apart from Mads drsstc 1 I haven't really seen bigger drsstc with helical primaries at all, unless having a pancake primary was more of the norm 5-10 years ago?
So my question is, are there any drawbacks from having a helical primary at this size I can't think of?
Post by: Mads Barnkob on April 10, 2019, 09:13:24 AM
For about a month now I've been put off on this project, I really couldn't be bothered making any progress and I couldn't figure out why..... Then it hit me! I hate the look of it 😢
Basically I had a 450x450x350mm "cube" for the base of the coil, to me that's pretty unappealing. One look I do like are round bases both a helical primary. Apart from Mads drsstc 1 I haven't really seen bigger drsstc with helical primaries at all, unless having a pancake primary was more of the norm 5-10 years ago?
So my question is, are there any drawbacks from having a helical primary at this size I can't think of?
Good old Dr. Spark, which seems to have closed down his website, primarily built helical primary coils and they performed great!
Now I built a helical coil on my first DRSSTC for several reasons:
- To make the coil take up less space, smaller diameter
- I thought it was easier to make primary coil holders for this type compared to spiral
- Tapping was easier with cable just going up the side
I will avoid helical coils in the future for the following reasons:
- It has a high coupling that is harder to adjust/control
- It is much closer to the topload, so there is more strikes to ground rail
- It was a pain to wind the coil through the 4 sheets with too small holes, it took me hours to move it centimeters at a time as it kept locking itself in place
- There is no performance gain over spiral, for a DRSSTC
I would however still make round platforms with spiral primary coils, as I think they look great, but when you get up in size you really need a bigger base to stabilize the thing with wheels out in the corners of a box.
You could also go inbetween spiral and helical and make a upsidedown U shape primary if you want it to have a smaller diameter overall.
Looking forward to see what you decide on :)
Post by: oneKone on April 10, 2019, 09:49:46 AM
Post by: Mads Barnkob on April 10, 2019, 12:21:20 PM
Cheers for the guidance Mads. Is having a upsidedown U primary the same calculation as a flat pancake? I had a quick look at your drsstc that uses one, looks extremely nice.
I think I just went with a median value based on spiral coil and coupling as if it was a helical, but as you can see from the article on my website, I did a lot of measurements instead, as I could not calculate its specifications.
I guess you have to use something like FEMM in order to get a correct simulation as spiral/helical calculators and javatc does not support that primary form.
Post by: oneKone on May 01, 2019, 12:51:07 PM
i made small progress by cutting out the new base for the coil, i like it so much more than the square frame i put together! for the primary i've drawn up a basic shape in aspire and have given roughly 10mm spacing. at this point i'm trying to decide if i should have my mmc at 330nf or 165nf. It's been a while since i've had to recall but the lower capacitance means higher number of primary turns which would result in a lower achievable apk? i will have to re-read a few threads again to get my understanding back!
this is what the coil looks like now and the proposed primary, which is 50mm high and 100mm long. on the weekend i'll make a better effort to get some more in depth progress photos.
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Post by: Mads Barnkob on May 01, 2019, 10:12:25 PM
I guess you can get away with just estimating that as a flat primary in JavaTC and it will not be too far off.
The higher MMC capacitance, the lower system impedance to a given resonant frequency. So yes that means higher peak currents, shorter on-time due to faster current ramp up etc. But it also gets more expensive to build due to increased cost on parts that can withstand the higher voltage/current. Higher impedance is cheaper to build but comes at the expense of greater switching losses due to longer on-time needed to produce long sparks.
Post by: oneKone on July 08, 2019, 03:57:17 PM
in my last update i made a mdf base and went with plywood primary supports. At the time i knew the supports weren't the best idea and i still wasn't happy with the base... it was time i changed the base again! which also brings me to distraction number one, a new cnc router! to me its a tool that i needed for many of my hobbies and will serve a great deal in coiling.
i wish i took photos during the design, cad and cutting but i didn't think ahead... i redesigned the base to be hex and made it out of plywood, i also made the primary supports out of polyethylene. I think once the base has been given a light stain the white from the mmc and primary supports as well as the primary and secondary should be appealing to the eye, not the most critical part of a drsstc but a part none the less. during the week i should have the coil wired up to begin testing, which is extremely overdue.
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Post by: oneKone on July 12, 2019, 01:23:58 AM
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Post by: Mads Barnkob on July 12, 2019, 09:56:38 AM
You should place your CTs at either output from the bridge, never between the primary coil and MMC, as you have a high voltage ringing between L and C.
Small progress is better than no progress! I am currently in a period of no progress, mostly due to starting on a new job and that takes all my mental capacity :)
Post by: oneKone on July 13, 2019, 03:48:54 PM
I think I have little time! I couldn't imagine your workload!
I got some light testing in tonight. One thing that I can't remember is switching times.. I'm going to have to ready your write-up again mads. Basically I'm getting turn on/off times of 1uS (1000ns?), Once I get better educated on switching times I can see if/what I'll have to change with the gdt. I'm also getting 5v overshoot, to me.this seems acceptable, but again it's something I'll have to read up on.
Another factor is that these tests were done without a topload so it will be interesting to see.if the lower frequency helps with the switching times.
Picture of gate waveforms for reference:
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Post by: Mads Barnkob on July 14, 2019, 02:06:26 PM
Post by: oneKone on July 21, 2019, 03:25:02 PM
I've had some time this weekend to work on the coil. I rewound the inductor as it was off the mark for what I needed, I also made the (but not finished) the topload.... As well as first light! At the moment i haven't made any measurements besides setting the phase lead.
While running up.the coil to about 1/2the input voltage it struck my router and killed a stepper drive, so all tests will now be done outside.. pictures!
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Post by: Mads Barnkob on July 27, 2019, 08:35:33 PM
A real shame about killing a stepper driver on your CNC router, get some metallic net/chicken fence and throw over it, grounded and it should be safe :)
Your topload looks really cool, Russian design inspired I see, but the pieces of pipe covering 180 degrees seems to be too little when you have a sharp edge on the "outside" of the virtual toroid, so you have a break out elsewhere than from your breakout point. You properly need another 20-30 degree inwards in each end, so you need 240 degree pieces of pipe.
Post by: oneKone on July 28, 2019, 03:16:38 PM
Congratulations on first light!
A real shame about killing a stepper driver on your CNC router, get some metallic net/chicken fence and throw over it, grounded and it should be safe :)
Your topload looks really cool, Russian design inspired I see, but the pieces of pipe covering 180 degrees seems to be too little when you have a sharp edge on the "outside" of the virtual toroid, so you have a break out elsewhere than from your breakout point. You properly need another 20-30 degree inwards in each end, so you need 240 degree pieces of pipe.
Cheers, and yeah.. I've learnt my lesson with bigger coils now!
As for the topload I'm hoping I can cut out another radius and just bend it by hand with the t-pieces soldered on. I know it was another group that first put the topload out there, but it was Finn hammer that inspired me to do it.
In other news I ran the coil successfully tonight! Managed 1.6m streamers even with the topload situation. MMC was cool to the touch. The bridge was ever so slightly warm so I might just add active cooling just to be safe.
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Post by: oneKone on August 06, 2019, 05:11:10 AM
I got a 20a capable outlet installed for possible future builds, but this also means I can easily run a a higher current limit. I've now verified the bridge with 900a @ 100us on time. One major thing I must fix is the toroid. I'm going to cut out a concave radius and try to push each segment in to try and form a new radius, if that fails I'll have to unsolder the joins. Hopefully this weekend I'll get some decent pictures of my setup and some arcs.... I'm truly Hoping for near 2m
Post by: fnordest on August 06, 2019, 10:56:30 AM
Post by: oneKone on August 14, 2019, 04:39:11 AM
Wow! Really nice, those sparks look amazing and the hexagonal base suites your coil very well :D
Cheers,
I'm pretty happy I went with a hexagonal base, definitely something I'll be using on future coils.
Another small update;
The ixys 40A 1200v bridge rectifier is dead! I ran the coil Hoping to get a few pictures and a video for the forum but unfortunately that couldn't happen. I'm not sure as to why it failed as the heatsink it's mounted to was barely luke warm (same heatsink as igbts). I've ordered a 150a 1600v bridge rectifier to replace it. When the fuse first blew I thought it was the bridge itself so I'm taking this as a win!
Post by: Mads Barnkob on August 16, 2019, 10:34:46 PM
You mentioned that your IGBTs heat sink got slightly warm on the first light run, how about your primary coil?
Post by: oneKone on August 19, 2019, 03:29:24 AM
As for the igbt heatsink getting warm, it's simply not good enough of me saying "slightly warm" or "barely luke warm". I'll get a probe on both next time I run it.
Post by: Netzpfuscher on August 19, 2019, 07:37:07 AM
The cooler you start your burst the more headroom you have to the max junction temperature.
That's the reason why my new coil has a big heat sink and a strong cooling fan.
Post by: Hydron on August 19, 2019, 10:44:35 AM
As for the OP's bridge rectifier going pop, was it due to the streamer hit to the primary?
Commonly accepted practice is to tie one side of the DC bus to earth via a moderate value capacitor (e.g. 100nf), so that any current from a streamer strike has a low-impedance path to earth from the primary. The theory is that if this low-Z path is not present then you may run the risk of internal breakdown of the IGBTs or diode bridge to the earthed heatsink they are mounted to. Not sure how tested it is other than Steve Ward removing his strike ring and encouraging arcs to hit the primary of one of his coils (without any damage), but it does make sense as a theory!
Post by: Netzpfuscher on August 19, 2019, 02:27:06 PM
The capacitor solution is a problem with RCDs, the high frequency ripple on the bus drives a current through the capacitor and this trips the RCD. I suggest to use two strings of TVS diodes from the inverter output to earth. (6x 100V 1,5kW)
Post by: oneKone on August 21, 2019, 03:59:47 AM
@Hydron the primary strike wasn't what killed the rectifier but I think it could have weakened/damaged it somehow, the failed when a greater input current was used.
Post by: Mads Barnkob on August 22, 2019, 09:32:24 PM
Post by: oneKone on August 29, 2019, 12:54:28 AM
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Post by: Mads Barnkob on August 30, 2019, 09:30:23 AM
Your coupling is too high or it is badly tuned when you get racing sparks, it can also be a insufficient grounding of the secondary coil.
I am actually not sure if varnishing the topload is a good idea, will it disrupt the electron charge and the toploads ability to have a surface capacitance, anyone can answer this?
Post by: Uspring on September 02, 2019, 12:09:49 PM
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I am actually not sure if varnishing the topload is a good idea, will it disrupt the electron charge and the toploads ability to have a surface capacitance, anyone can answer this?
The varnish will have two properties. It will be a dielelectric and an insulator. As a dielelectric it will be polarised, causing an electric field opposite to that of the top load. Since it is a volume effect and the varnish probably thin, there will be a negligible increase of top load capacitance.
As an insulator, the varnish won't stop the appearance of an electric field around a charged up top load. Near points of high curvature, ionisation of the air will occur. If the top load is say, at a high positive voltage, the free electrons created will be attracted to and stick to the varnish and generate an electric field opposite to that of the top load. Eventually, this will stifle the ionisation.
But once the top load voltage reverses, the stuck electrons will increase the field and ionisation will start again. This time positive ions will stick to the varnish. So you will have some ionisation on each cycle.
Another way to see this is, that the varnish will act as an insulator of a capacitor, insulating the top load from a more or less conducting volume of air around it. And a capacitor is an AC conductor. The appearance of racing sparks along secondaries and primary secondary flash overs illustrate, that high frequency voltages don't really care about insulators. But they do help somewhat.
The long breakout rod you use is certainly a good idea. The breakout from there reduces the top load voltages. But the best option is to avoid sharp edges.
Post by: oneKone on September 03, 2019, 07:27:17 AM
As it stands time is running out in this coil for the year, as summer approaches the days get longer so I won't be able to run the coil 😓
Post by: oneKone on October 06, 2019, 04:31:55 PM
After trying for a while to get the spiral toroid working i finally listened to @Acid Byte. A quck trip to the hardware store and a few cuts on the cnc router later i had a new toroid! the diameter is 700mm with a height of 150mm. I also started to get working on the active cooling, it's simply a 3d printed box to house two hp server psu fans. I'm hoping to get some real runs in and fine tune the setup this upcoming friday... until then some pictures!
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Post by: Mads Barnkob on October 07, 2019, 12:37:44 PM
You properly had to de-tune the primary some more? Noticeable enough to have higher peak current and thus getting longer sparks from a lower impedance system?
Post by: oneKone on October 08, 2019, 12:56:35 AM
Yes the tuning changed quite a bit, I think something like 18khz or more. I still have fine tuning to go. To be honest I'm not sure what it would normally pull before as I had the OCD set to 900a.
One thing I've been thinking about making is essentially a vu metre for current, have the leds in 100a steps 🤔
Post by: Mads Barnkob on October 08, 2019, 12:22:54 PM
Cheers,
Yes the tuning changed quite a bit, I think something like 18khz or more. I still have fine tuning to go. To be honest I'm not sure what it would normally pull before as I had the OCD set to 900a.
One thing I've been thinking about making is essentially a vu metre for current, have the leds in 100a steps 🤔
I actually made such in 2011 and never finished the project :o It was based around a cheap DMM IC called ICL7017 and a VU meter IC, guess microcontrollers like Arduino surpassed that project by now. But it was meant to just be a homemade CT and a 0-2000A display + VU meter.
Post by: oneKone on October 23, 2019, 09:09:26 AM
Cheers,
Yes the tuning changed quite a bit, I think something like 18khz or more. I still have fine tuning to go. To be honest I'm not sure what it would normally pull before as I had the OCD set to 900a.
One thing I've been thinking about making is essentially a vu metre for current, have the leds in 100a steps 🤔
I actually made such in 2011 and never finished the project :o It was based around a cheap DMM IC called ICL7017 and a VU meter IC, guess microcontrollers like Arduino surpassed that project by now. But it was meant to just be a homemade CT and a 0-2000A display + VU meter.
If I ever get around to it I'll post it up, to me it's an easy way to see what's going on..
I think this might be the last update on this coil 🤷♂️.
Final OCD is set to 900a, pulling 15a arms from a 230v outlet @ 100us. I'm getting over 2m streamers at 100us, I'm tempted to push it but I'm also happy with the results. I'm also happy as this is the first drsstc build that I've done with an almost 100% success rate, with the bridge rectifier being the only part to fail!
All in all I'm happy and am keen to get onto my next builds. So far my upcoming builds will be a small 180khz skm100 fullbridge coil, and some gu50 tube projects! Ad well as the big dr project...... That's a lot on the horizon!!
Some pics:
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