Micro drsstc

[oneKone]

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.

[oneKone]

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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[oneKone]

With the death of half the fullbridge it's time to redesign the layout to be more modular!

[oneKone]

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!
 

[Mads Barnkob]

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!

[oneKone]

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........

 

[Mads Barnkob]

Shipping is not cheap, but price per brick is okay: https://www.ebay.co.uk/itm/Mitsubishi-Leistungs-Modul-High-Power-CM300DY-24H/142765464615

[oneKone]

cheers mads, i ended up buying all 3.

[Hydron]

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).

[oneKone]

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!

[oneKone]

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!   

[Mads Barnkob]

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!

[oneKone]

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...