High Voltage Forum

Tesla coils => Dual Resonant Solid State Tesla coils => Topic started by: oneKone on February 27, 2018, 03:19:48 AM

Title: Micro drsstc
Post by: oneKone on February 27, 2018, 03:19:48 AM
After completing a version of mads drsstc ii I've now caught the drsstc bug! So time to get building a new one.

The secondary was originally wound for a sstc but the fres seems low enough for a small to-247 half bridge setup, in which i'll try some 60n60 igbts from aliexpress.

current actual/ calculated specs;

Secondary: 76 mm od, 129 mm long, 104 mm winding length, 0.13mm wire, about 800 turns
Topload: 160mm diameter, 40mm high spun aluminium toroid. Secondary and toroid give 370khz
Primary: aiming for 7 turns of 3.2mm copper tube tapped at 4.8 turns
Primary resonance capacitor: 47nf  Cornell-Dubilier Polypropylene 3kv
Full bridge of to-247 60n60
Driver: a steve ward 1.3b variation from ebay
___________________________________________

One thing i might try is to wind a dual? 1:33:33 ct using 3 epcos n30 ferrite rings (https://au.rs-online.com/web/p/products/2120982/). something similar to loneoceans drsstc 3 ct arraignment. The last time i ordered one of these driver it took quite a long time to get here. so potentiality this project could appear to be abandoned, in reality it would be me waiting for parts to arrive. 

core to the left*




Title: Re: Micro drsstc
Post by: CCX191 on February 27, 2018, 05:17:19 AM
Looks like I have returned at the right time! Looking forward for more!

Sadly I still I can't work on my coil till June :-\ College is indeed stressful.
Title: Re: Micro drsstc
Post by: oneKone on March 07, 2018, 12:38:54 AM
Cheers @CCX191

A small update, the ct cores and resonant capacitor have come. Just waiting on the driver itself and the igbts. I don't think I'll start building until everything arrives.
Title: Re: Micro drsstc
Post by: oneKone on March 13, 2018, 02:52:00 PM
Another small update!

i have pretty much all of the components minus the driver so i'm thinking i might get started on the construction. Originally i was going to try a halfbridge of 60n60 igbts but i might try a fullbridge. The way i'm thinking of constructing it is a point to point style. I've attached a picture of what i'm thinking about going with.
Title: Re: Micro drsstc
Post by: Mads Barnkob on March 14, 2018, 10:33:10 AM
Minimalist bird nest is good for low inductance, but it can be hell to take apart when a IGBT blows up. So try to think replacement into your layout.

Two individual heat sinks will properly also make it easier for you to have access with wires for DC bus and inverter output.
Title: Re: Micro drsstc
Post by: oneKone on March 14, 2018, 02:18:45 PM
cheers for the advice about the inverter layout.  Before checking to see if there were any replies i ended up making the inverter. I guess ill see how much of a pain it will become in the future! I also received the ebay driver board. looking over it and by the markings it appears to be a ud3 variant.... i have absolutely no knowledge of the new drivers, hell i have no knowledge of the 2.7c!   




Title: Re: Micro drsstc
Post by: Hydron on March 14, 2018, 05:08:03 PM
It's not a UD3 (that's a completely different design based on a PSoC 5LP - see the "Next Gen DRSSTC" thread), but the driver is definitely of interest - if it works well it could be a useful option for a pre-built, cheap driver. Please let us know how it works - I'm not sure anyone has tried this one before!
Title: Re: Micro drsstc
Post by: oneKone on March 15, 2018, 12:38:08 AM
Thanks for clearing that up Hydron, I'm way out of my depth past the 1.3b driver. After a bit of digging I've found this thread on 4hv.

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?179388
Title: Re: Micro drsstc
Post by: oneKone on March 17, 2018, 12:54:10 PM
small update....... the driver doesn't work! i looked over all the basics, feedback ct phasing, tried changing the gdt phasing, replaced the feedback ct with a function generator and finally ran the coil/ inverter with a sstc driver, which works awesome! i honestly think the driver is just doa. I think the biggest problem with buying drivers like this is there's very little to no information on other forums or documentation. I'm going to try a bit more digging and contact the ebay seller to see if he might have any more information on it.
     
Title: Re: Micro drsstc
Post by: futurist on March 17, 2018, 02:51:53 PM
Sorry to hear that. Does it produce any output on the GDT?
Title: Re: Micro drsstc
Post by: oneKone on March 18, 2018, 02:00:59 AM
Sorry to hear that. Does it produce any output on the GDT?

i thought it did but after read your comment i checked again. The tc4423 was only outputting one side of its outputs, so after desoldering and soldering flyleads to a ucc27425 it now works! But..... it only starts oscillations at 250v input so i emailed the seller asking for a user manual. it seems the the 1:33:33 feedback ct is too large?

All that aside i did manage about 300mm streamers to free air! it wont play midi but i'm hoping after i can get some documentation i can get it working properly.

Title: Re: Micro drsstc
Post by: futurist on March 18, 2018, 11:22:53 AM
it seems the the 1:33:33 feedback ct is too large?

Probably yes, what is your primary current? Steve wrote somewhere that his driver works best with about 1 A of feedback current
Title: Re: Micro drsstc
Post by: oneKone on March 18, 2018, 12:53:30 PM
It's running about 200a primary current.

edit:
even with a 1:200 ct for the feedback the operation hasn't changed. i have also ran it without a feedback ct and it performs the same so it obviously has another part damaged on the board.
Title: Re: Micro drsstc
Post by: futurist on March 18, 2018, 02:28:22 PM
You can try with 1:15:15 CT which gives 1:225 ratio
I tested that CT for feedback in my 40N60 DRSSTC inverter and it works fine, even with 30 V on the bus
Title: Re: Micro drsstc
Post by: oneKone on April 09, 2018, 05:58:29 AM
I just received the new driver, so now the project can get back on track!  I've been thinking for the frame I might use 15mm PVC pipe and fittings. I think this way could be perfect for a small coil, light and modular.

The driver is the ud1.3b through hole equivalent and it included a small transformer, although I bought an 18v SMPS for the driver.

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Title: Re: Micro drsstc
Post by: oneKone on April 09, 2018, 12:09:00 PM
So I basically pushed over other small projects on my desk and quickly had the coil running. All I can say is that I'm excited to get this finished and tuned now! Rough calculations put the streamers to about 370mm. I have a 14 second video on coilsmiths (Facebook's page)
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Title: Re: Micro drsstc
Post by: Nijin on April 09, 2018, 10:05:50 PM
Good job !

I plan to make a similar small drsstc. What is your coupling coefficient k ?

Title: Re: Micro drsstc
Post by: oneKone on April 10, 2018, 02:10:30 AM
Good job !

I plan to make a similar small drsstc. What is your coupling coefficient k ?

 Cheers.

To be honest I've never calculated the coupling coefficient. i calculated it in javeTC (which I've never used either!) which calculated it to be 0.45, the recommended was 0.13.
Title: Re: Micro drsstc
Post by: oneKone on April 10, 2018, 11:35:10 AM
I've almost finished building the coil.... Packing everything into a small form factor is hard! One thing I've realised during testing is that I'll need active cooling, without it the heatsink gets pretty warm after about 15 seconds of playing a midi track.

In one run (assuming I scaled it correctly) I had almost 450mm streamers to free air! The tight coupling has been a bit of a pain but i think I can get it under control.


Title: Re: Micro drsstc
Post by: Mads Barnkob on April 10, 2018, 10:01:27 PM
That looks awesome oneKone!

That is one powerful little coil you got yourself built there and with 0.45 coupling don't you have problems with racing sparks or flashovers? If not, you must have hit a good tuning point where you transfer all your energy :)

Do you have youtube to you can just put video link in post to embed the video?
Title: Re: Micro drsstc
Post by: oneKone on April 11, 2018, 02:38:56 AM
Cheers mads.

Racing sparks are a bit of a problem, I've tried spacing the secondary 15mm up from its original position. This seems to have fixed the problem, so my coupling would be less now but I'm not sure by how much. I have one last part to make for the coil so hopefully I'll get a video up tonight.

Title: Re: Micro drsstc
Post by: oneKone on April 11, 2018, 03:35:23 PM
The coil has had its first successful full midi run! The song was about 40 seconds long. The fan I put on the heatsink might need to be upgraded, it keeps it cool enough for one track but there's always room for improvement.

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Title: Re: Micro drsstc
Post by: oneKone on April 21, 2018, 03:21:54 PM
With the death of half the fullbridge it's time to redesign the layout to be more modular!
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Title: Re: Micro drsstc
Post by: oneKone on April 23, 2018, 12:55:43 AM
i think this may be the last update on the micro drsstc, unless i make a new base/frame for it.

Half of the Fullbridge died from the ocd limit being set too high, setting the ocd with a theoretical limit is obviously not the way to go but with free air streamers it was fine on this small coil. I've now set the ocd at about 210A (measured with an oscilloscope).

this was the run that killed it, nothing spectacular just a silent death!
 
Title: Re: Micro drsstc
Post by: Mads Barnkob on April 23, 2018, 09:25:05 PM
RIP micro DRSSTC!

You got some good results while it lived, but it also serves to show that when things are pushed too hard they are short-lived :)

You just need something with a larger mass to absorb the impulse temperature rises, get bricked!
Title: Re: Micro drsstc
Post by: oneKone on April 24, 2018, 09:59:13 AM
RIP micro DRSSTC!

You got some good results while it lived, but it also serves to show that when things are pushed too hard they are short-lived :)

You just need something with a larger mass to absorb the impulse temperature rises, get bricked!

sorry, i'm an idiot! 

The coil lives happily now with a new current limit set, although i haven't tested it with multiple ground strikes. i know in the future it will die again because i do hammer it quite a bit! but igbts are cheap from aliexpress. i'm keen to get my hands on a pair of cm300du-24 bricks! The new coil start is very close........

 
Title: Re: Micro drsstc
Post by: Mads Barnkob on April 24, 2018, 12:34:11 PM
Shipping is not cheap, but price per brick is okay: https://www.ebay.co.uk/itm/Mitsubishi-Leistungs-Modul-High-Power-CM300DY-24H/142765464615
Title: Re: Micro drsstc
Post by: oneKone on April 24, 2018, 02:42:09 PM
cheers mads, i ended up buying all 3.
Title: Re: Micro drsstc
Post by: Hydron on April 24, 2018, 04:36:38 PM
Good buy assuming they are as described! Seemed to be the same cost to ship down under as to non-german Europe, which makes it far less painful if you're buying from that far away.

I am using the exact same modules in my 160mm coil at ~750A/70-80kHz, and I suspect I could push them significantly further (but already got >2m streamers at that current).
Title: Re: Micro drsstc
Post by: oneKone on April 25, 2018, 02:58:51 PM
i'm also hoping they work and get a decent running life. i ended getting 4 euro off each brick! as for shipping..... we aussies are a custom to paying a lot! in my opinion one of our main postal services (auspost) are the biggest joke going, but i could go on all night about them!

i'll have to re-read your drsstc thread, i would love to get around 2m streamers but i may be limited..... unless i do full power runs at the front of my house!
Title: Re: Micro drsstc
Post by: oneKone on July 14, 2018, 04:18:17 AM
so this is going to be a thread that might continue for a bit longer!

The coil has had mixed success/failure with blowing igbts. So i thought i'd dive into it and find the problem! the first thing i tried was rewinding the gdt. While the first one worked i never really scoped it in the config it was in because i knew it could work with these frequencies, or so i thought. The waveform was beyond a joke! so i rewound it with 13 turns of Ethernet wire (sheath removed) this gave a way better result, but still with slight peaks although i'm not too worried (sorry no pictures yet)

The second half of my problem was finding decent chinese 60n60. For a while i tried all different vendors until i found a ebay seller that had IXYS IXGN60n60C2 devices. I guess the only downside is that these do not have integrated tvs diodes, so for this i am just using mur1560 (i actually wonder how much i am punishing these) . With these two changes i started getting racing sparks at 30us on time. To me this was a clear indication that the previous gdt and switching devices weren't up to the task. Along with the racing sparks i also blew another 2 sets off fullbridges from the arcs hitting the primary and blowing a hole through the igbt to the heatsink.

After still not having the greatest luck i switched it to a halfbridge and it's been loving life! the igbts stay cool and tests so far look promising. The free air discharges have reduced from about 450mm to 270mm and the peak current (with free air midi) looks to be in the 120A range. I'm happy with 270mm because thats still 2.7 X secondary length but i'm also determined to get longer arcs again! I think the next plan of attack is to make a spiral primary and try a fullbridge setup again.

Another thing that i could also achieve is twin coils! I started winding another secondary for someone that didn't want it in the end so i'm wondering if i shouldn't just build the exact same as the first and look into a 2 channel midi interrupter. Then hopefully this project will come to an end!   

Wow so yeah, that was a lot!  looking forward to feedback as to what path i should go down as i'm pretty indecisive!   
Title: Re: Micro drsstc
Post by: Mads Barnkob on July 16, 2018, 08:19:13 PM
It sounds like you also had a too high coupling issue if you had racing sparks at such low on-times.

I think the MUR1560 is doing well for the job, only issue could be that its not exactly sharing the same thermal mass as the IGBT.

You should try to fine tune it for higher peak currents at same or shorter on-time, or simply longer on-time to grow the sparks.

I vote for a twin coil and dual midi!
Title: Re: Micro drsstc
Post by: oneKone on July 23, 2018, 01:41:55 PM
man...... getting a reliable source of consistent igbts is hard! i ordered one batch that worked flawlessly... but this batch i've had 2 sets of fullbridges die within minutes of operation. I've tried to keep a low inductance throughout the design so i wouldn't have to use snubbers.... i'm not sure if this is now for some reason biting me in the ass...

Edit:
I've ordered new TVs diodes incase one of them is damaged, I'm also going to get new gate resistors then scope the output and maybe even the bus voltage to see if there's any ringing.  The strange thing is that with a halfbridge setup it works flawlessly so it must be a tvs problem...