My (First) Mini DRSSTC

[Manz]

Hi, I'm Andrea, 19 yo from Italy.

After building a small sgtc with scrap parts in middle school I've always wanted to make a drsstc and I found all the threads on this forum very helpful so I really hope the information in this post will help someone in the future.

So here are some details about my coil:
-Secondary coil: 10*38cm, about 1900turns of 0.2mm wire for a resonant frequency of around 120kHz with topload (10*35cm aluminum duct)
-Primary: 7 turns of 3.5mm copper tube around 4.5meters long
-MMC 6kV 88nf  4p 22nf 6kV MKP capacitors
-Inverter fullbridge of fgh60n60smd, 2000uf 450V bus capacitor using 2 electrolytic cap in parallel. Everything on a diy pcb made with a dremel hoping for low inductance and a compact design (a nightmare if something breaks but it never happened until now)

As I wanted to learn as much as possible I decided to design the driver by myself.
It uses 2 flip flops for ZCS so it can shutdown during rising and falling edge. This way I have more control over the ontime (better for midi) and the OCD kicks in faster (it's not necessary but I just thought it's cool so I added it)
It has a rudimental UVLO and uses 2 UCC3732x to drive the bridge.
To avoid using the variac a relay charges up the bus cap via a 10W resistor and when the coil is disconnected from mains it's discharged via another resistor for safety reasons.

the coil is overhall 70cm tall and capable of 1 meter long sparks but I usually set the OCD to 300A and get around 70-80cm air streamers with 50uS on-time.


The coil performing at the Trieste Maker Faire easily striking the groundwire 70cm away


I don't have any good scope shot to show you as I don't have an oscilloscope but I was able to test everything using my school's scope and differential probe. (it's been a long time since I took those pics so I don't remembere the details, I'm sorry)
Inverter output
Primary current


And one shot of the primary current going up to around 200A



The MMC failed just as I was writing this post but it's not a big deal as I already have spare capacitors.
(failure probably caused by the unshielded driver and bad grounding which caused an overcurrent event on the primary)
I'm already working on a skm100 fullbridge to upgrade the coil when my to247 inverter will fail.


In the end this build was a great succes for a first coil and I just had the first failure now, after a bit more than 6 months of almost daily use. I'm proud of this coil and I can't really thank Felix B. enough for all the help he gave me and Mads Barnkob for the DRSSTC design guide that also helped a lot.



If you are interested in some videos of the coil in action you can find them on my yt channel

[Mads Barnkob]

Andrea, that is a great build for your first DRSSTC and what a challenge to step it up with making your own driver!

The size of the coil certainly deserves a better MMC and larger bridge, you will not regret these upgrades. Just watch not melting something else, like the secondary coil or primary wirings

Great video, subscribed to your channel, hope to see more.

[dru]

Hi Andrea, very well built coil! You mentioned making your own pcbs, and I was wondering if you have any tips. Right now for making mine I use a laser printer to print the traces on transfer paper, then heat press that onto copper clad, then etch. The traces usually come out clean, but I've found when tinning them the heat can sometimes cause the traces to peel off. I'm not sure if I'm maybe using too high heat, or leaving the board in the etchant too long. Have you encountered this problem?

[Manz]

Thanks for your kind words everyone

I made a pcb with a dremel for the fullbridge as it is pretty easy and there is plenty of margin for errors, I couldn't do it the same way for the driver as more precision is required, I thought about etching the pcb by myself but in the end it was probably cheaper and less time consuming to just order it, so that's what I did.
I think I'll try to etch my own PCBs in the future as it seems quite fun

[RoamingD]

Hello, congratulations on your build  , would you care to share the interrupter that you used ? and maybe an schematic/explanation if you have time 

[Manz]

Thanks.
I'm sorry but the interrupter is designed by Felix B. and he's not willing to share it at the moment so I wont do it.

[Manz]

Hello everyone, a little uptade.
I'm currently upgrading the coil to run it on a fullbridge of skm100 (you can see a picture of it in my first post) using a ud2.9 in pulseskip mode.
As I have no experience with pulseskipping I'm wondering what kind of onTime and primary current do I need to notice any change compared to standard drsstc mode. And if my bus cpacitor is too small (450V 4700uf).
I guess theres no definitive answer and I will have to run the coil by myself but if anyone with some experience has anything to say I'll appreciate it

[Manz]

Hello everyone,

I just wanted to let yall know I upgraded the coil as per last post so it now runs on a skm100 fullbridge, 4700uF bus cap and a nice 10p4s mmc for a total of 97.5nF 8kV.

I decided to set the OCD to 300A and run it in pulseskip mode up to 500us. Usually 100-200uS in MIDI mode.
it performed without issues for over a year now and I'm really happy with it as it is basically a tabletop, easy to transport coil but can generate sparks well over a meter in length.

I really wanted to make a good thread out of this one but documenting everything while building it, learning stuff, changing ideas and plans is really hard and time consuming.
Maybe someday I will release my old driver capable of shutting off at both positive and negative edge as I think it is quite cool.
I hope at least I've managed to inspire someone to start building and experimenting with Tesla coils, just as everyone on this forum has inspired me back in the days.

A couple of pics of the coil (plus a sneak peek at my ramped SSTC)








PS
I was able to get my hands on a midistick, I can't wait to try some good music and effects

I hope you guys enjoyed reading about this build and I wish you all good luck!

best regards,

Andrea