Kaizer DRSSTC IV - Poor mans QCW

[Mads Barnkob]

I'm sorry to hear about the demise of the project.

I tried tuning the coil at 120 kHz and 130 kHz, way above the estimated loaded secondary Fres of 88 kHz. When I ran the coil and zoomed in on the current waveform, it was oscillating at 175 kHz, I am not even sure what is going on anymore

Given enough coupling that is what you'd expect. The problem with running at the upper pole is, that arc loading will move the secondary res frequency away from the operating frequency thus increasing primary current, which will lengthen the arc. That is a positive feedback situation. Running at the lower pole the feedback will be negative, stabilising the primary current.
I don't think the variacs inductance plays a role as long as you have a large enough cap on the DC bus. Large enough means, that the voltage drop on the DC bus cap due to the primary current (i.e. using primary current frequency and amplitude) is much less than the bus voltage.

I am only calling quit on it because of the induced voltage spikes in the mains supply, I was warned about this before moving into testing it, but if you look at the video and see that blue, inverter voltage output has spikes up to around 750V, it is not pretty on the output, I do however not have any measurements from the variac output, but as the voltage meter broke in it, I guess it was bad enough

I only had 10 uF of DC bus capacitance, in form of a snubber.

I guess this my first adventures into running a coil at the upper pole, which is normally much closer to the lower pole in a regular DRSSTC, but as you can see, tuning this primary over a span of 60 kHz doesn't really change that much

A future for this could be a new 300+ kHz secondary coil, less primary turns and so on

[Dylan Burger]

I am glad you got the issue of oscillation failure worked out. That is a nice output

I am guessing there would be no efficient way to snub the spikes induced to your mains supply ? 750v is nasty.