Flanging sound coming from DRSSTC

[Coileone]

Good Afternoon,

I'll try my best to describe this as accurate as possible.

When I turn up my pw to around 500-800 us @ 50 bps, I begin to hear a flanging sound. The sound starts out with a higher pitch flanging sound and progresses to a lower pitch as I turn up the pw further. At around 700-1ms, the sound is gone and doesn't return if I continue to increase the pw further.

The same thing happens with 150bps, but the sound starts earlier.. at a lower pw.. not sure exactly but id say between 100-400us? It also has the same behavior as above.

The sound is NOT coming from the streamers.

My output has the longest arcs right before the flanging sound starts. The output still increases as I turn up the pw, but mainly thicker streamers, not length.

Does anyone have a similar experience as this? It doesn't seem to be an issue, but it could be. Idk.. I would just love to understand why its doing it.

Not sure if this will help, but here are the specs:

6 x 28 secondary 27awg 1550turns ish
6 x 28 Toroid
95khz ish res freq
3/8" Flat Copper Primary tapped around 6.5 turns
6s/13p 325nf 12kv MMC (78 CDE .15uf @ 2kv)
(2) CM400-12 Full Bridge
(2) 4700uf parallel = 9400uf @ 450v bus caps
208v In - 290vdc bus
UD 2.7C w/ OCD @ 1000amps
EVR Interrupter 1.0

Thank you for taking the time to read this. Hope all is well!

Kyle

[klugesmith]

Can you post an audio recording of the "flanging sound" of which you speak?

[davekni]

Scoping current waveforms before and after onset of "flanging sound" might also help.  Even better would be both current and H-Bridge output (or UD2.7 output to GDT if you don't have isolated or differential probes).

[Coileone]

Can you post an audio recording of the "flanging sound" of which you speak?

Sure! It starts around 4-5 seconds into it.

https://youtube.com/shorts/hJkYXoYHmwE?feature=share

[Coileone]

Scoping current waveforms before and after onset of "flanging sound" might also help.  Even better would be both current and H-Bridge output (or UD2.7 output to GDT if you don't have isolated or differential probes).

Ok. I will try that. Thank you for your feedback. 

[Mads Barnkob]

I think that is just a artifact of matching on-time / breakrate that produces some overtone or harmony like situation.

You are running very long on-time and when you say its there at 50 Hz and 150 Hz, you are at the fundamental and harmonic frequencies of the mains supply frequency? It could be that you are discharging right where your DCbus is being charged, if DCbus capacitance is too low, you could get some harmonic induced ramping going on.

[davekni]

Sure! It starts around 4-5 seconds into it.

Agree with Mads.  I don't see or hear anything indicating a problem.  Might be a transition where the base of the previous arc is hot and ionized enough to make the next enable pulse start immediately with significant arc length.  If bridge voltage and current are still properly phased (ideally bridge output voltage switching slightly before current zero-crossing), it should be fine.

[Coileone]

Sure! It starts around 4-5 seconds into it.

Agree with Mads.  I don't see or hear anything indicating a problem.  Might be a transition where the base of the previous arc is hot and ionized enough to make the next enable pulse start immediately with significant arc length.  If bridge voltage and current are still properly phased (ideally bridge output voltage switching slightly before current zero-crossing), it should be fine.

Oh, I don’t feel there’s any issue. My post was to learn and understand more about the coil and why certain things do what they do etc. Thank you

[Coileone]

I think that is just a artifact of matching on-time / breakrate that produces some overtone or harmony like situation.

You are running very long on-time and when you say its there at 50 Hz and 150 Hz, you are at the fundamental and harmonic frequencies of the mains supply frequency? It could be that you are discharging right where your DCbus is being charged, if DCbus capacitance is too low, you could get some harmonic induced ramping going on.

It’s there between those freq. That’s the lowest and highest bps settings on my interrupter. My bus capacitance is 9400uf so I kind of assumed that was plenty unless I’m mistaken?

I will agree it does sound like something harmonic related.

Not sure if this is relevant but the sound begins when my bus voltage drops to 265-270v