SSTC interruptor not working

[juuzpo]

Hello, i have built medium sized teslacoil (550mm tall, 110mm in diameter), and im using this schematic for the driver: https://www.stevehv.4hv.org/SSTC5.htm
I been running it with 30VAC instead of 230VAC so i don't burn the mosfets, and it produces about 5cm arcs.

The problem is that interruptor seems to do nothing. Even if i tie the ENBL pin of both gate drivers (UCC372x) it still produces arcs. Has anyone else encountered this problem?

[Mads Barnkob]

Do you have any unused IC input pins? You should tie all these unused inputs to ground, else you risk cross-talk inside the IC from EMI.

I assume you already double-checked your traces for errors etc.

[juuzpo]

Ok, update to the problem.

I got the interruptor working(ish) by having a really short antenna, however it worked very poorly; switching between interrupted and cw.

Then i made a oscillator with frequency range of ~200khz to 400 khz and connected it to antenna input. By tuning the oscillator right, the interruptor and coil worked OK. Sound was coming through, as my interruptor goes from ~100hz to 500hz.

This was all still with 30VAC. Then i decided to use it with 230VAC. First i plugged in just the bridge circuitry, it was stable. Then the control circuitry and after a second, the fuse went off (10A). The mosfets died (didnt explode though) G, D, S all shorted together. The interruptor was running with minimal duty: ~2%.

Was it the inrush current that killed them? Should i have some kind of power conditioning?

[Fumeaux]

I don't think that it was inrushcurrent. Did you calculate how much reactance your primarycurcuit has? And therefore how much current should flow?

If it worked with 30V before, my guess is that your primary reactance is too low.

Btw: The dutycycle doesn't really matter in terms of limiting current, just the heat generation.

[juuzpo]

Changed my primary from 4 turns to 8 turns and made the diameter larger, now the interruptor doesn't work anymore...

And the coil works otherwise strange too, it produces sparks with primary connected either polarity, or GDT primary connected either polarity.

[Laci]

The problem is that interruptor seems to do nothing. Even if i tie the ENBL pin of both gate drivers (UCC372x) it still produces arcs. Has anyone else encountered this problem?

If both enable pins are tied to ground, there should be no gate driving, so no arcs. The interrupter should always work accurately, unless if you have noise problems.
Have you grounded the unused inputs of the 74HC14, as Mads suggested?

Please upload some pictures about the driver, inverter, coil, etc.

[juuzpo]

The unused input pins are tied to GND. I'll post pictures of the coil and interrupter later.

The ferrite is manganese-zinc.



(Don't mind the soldering on the capacitor, it is just temporary solution  .)

[Laci]

Neat setup. 
I'm worried about your ferrite core. It should be a high permeability core. If you have an oscilloscope you can check the gate signals at low voltage while operating(be careful with the ground leads of the scope) or connect a function generator with your running frequency to the antenna input without voltage on the bridge.

If you have noise problems, maybe grounding the heatsink could help too.

[juuzpo]

Neat setup. 
I'm worried about your ferrite core. It should be a high permeability core. If you have an oscilloscope you can check the gate signals at low voltage while operating(be careful with the ground leads of the scope) or connect a function generator with your running frequency to the antenna input without voltage on the bridge.

If you have noise problems, maybe grounding the heatsink could help too.

Thanks, i have another core that is nickel-zinc. Maybe i'll try that.

I have this whole circuit in aluminum box that is connected to RF-ground (100cm x 30cm steel mesh). I have also shielded cable from the 12V supply and interrupter/oscillator, though i'm not sure which ground i should connect the shield to.

[juuzpo]

 Here's the secondary:

[SAMGO]

Hi,
Maybe you can try to put the enable pin of both ic to gnd and with an oscilloscope or if you didn't have one with a multimeter watch that it's really 0 to max 1.7V  like is written on datasheet. Put the measuring tool direclty on the pin so that you are shure of the measure. You can also try to make the same thing with the tesla ON and OFF and search for difference between measurement.