OCD Triggering Early + Low Output

[Saattvik24]

I finally got my first DRSSTC up and running and I'm very happy that it's working, but there are still some issues.
https://youtube.com/shorts/LW7HfMb8ZDw?feature=share

The OCD is currently set to around 350A but it gets triggered when the input voltage reaches around 130VAC yet the sparks I'm getting are still very short. To check if this was an issue with my tuning or not, I removed the secondary and replaced it with a solid piece of metal as the load on top of the primary coil. The OCD still got triggered at around 130VAC input.

I scoped the current waveform using a voltage probe across the 51ohm resistor and got following waveform. The peak voltage is 23.2V which translates to 284A in the primary (I'm using 1:625 reduction CT) Because the primary current looks good I thought I had just tuned it like shit. But I had calculated the secondary resonant frequency using a function generator and an oscilloscope and it came to be 153kHz. So I adjusted the primary tap till I could see the primary current having a frequency of approximately 143kHz (Detune of 10kHz) but still I was not impressed with my arc output. And I couldn't increase the input voltage cause then the OCD LED would be constantly on.


Then I proceeded to scope the comparator inputs for the OCD. The blue waveform is the set point, currently set to approx 2.8V which translates to 343A as the limit. The yellow waveform is the other input of the comparator coming from the feedback. Both of the waveforms have more noise than usual because I had to attach jumper wires to the header J9 so I can easily probe these voltages. The waveform is just when the OCD got triggered.


I'm not sure what the issue is, one possibility is that the ferrite cores I'm using for the CT are not good, as the N30 cores I had ordered were too small, so I had to use some other cores I had laying around. But I had tested them by making a GDT with them and connecting them to the output of the UD2.7C output while using a function generator as the feedback. The output waveforms looked good so I assumed the cores were good enough to use for the CT. (The core for the final GDT is big and of N30 material so that's not the issue)

Other than that I think I've done everything properly, maybe the primary tap is a bit janky but it hey it works. I've attached images so maybe you can figure out if I've done something wrong.

[davekni]

I'm not sure what the issue is, one possibility is that the ferrite cores I'm using for the CT are not good, as the N30 cores I had ordered were too small, so I had to use some other cores I had laying around. But I had tested them by making a GDT with them and connecting them to the output of the UD2.7C output while using a function generator as the feedback. The output waveforms looked good so I assumed the cores were good enough to use for the CT.

Did you test both core types within CT?  First stage gray/black core is likely ferrite.  Second stage green cores are more suspect.  Also, UD2.7 GDT drive is reasonable low impedance, so may make somewhat reasonable waveforms even on a poor GDT core.

However, I'd guess that CT core type isn't the main issue.  Might become more of an issue when tuning phase lead.  Without JavaTC information or some other basic specifications for your coil, hard to guess at issues.  284A may not be sufficient for your coil design.