Le Koo Cee Dubloo

[Uspring]

@Teravolt:
The frequency, the DRSSTC runs on, is determined by the zero current switching condition on the primary tank. The frequencies at which this happens never really match the secondary resonance frequency. If you're outside the resonance, it is often better not to have a too large Q.

@Hydron:
From the diagram you show, it looks like the lower pole is at 225kHz and the upper pole at 360kHz. The Z peak at 245kHz corresponds AFAIK to the secondary resonance. I'm wondering about your statement of secondary res being around 300kHz. It looks like primary fres could be about 300kHz as you state.

Upper pole operation is no surprise under this condition, since during the initial phase of primary rampup there is little current in the secondary, which could affect the primary. So it will start at the primary res frequency. When secondary current picks up, the coupling takes effect and the operating frequency moves up to the upper pole. I believe, that startup at the primary fres is generally the case unless special precautions are taken in order to start at a different frequency (e.g. a PLL).

But: Upper pole operation has an advantage over lower pole operation only if the primary fres is below secondary fres. And it should stay that way even under arc loading. I've illustrated this here: https://highvoltageforum.net/index.php?topic=78.msg624#msg624
If primary fres gets over secondary fres, the upper pole, at which the coil is running, will be pushed away by the coupling from secondary fres. That will impede power transfer to the secondary. Have a look at the paragraph "Tuning Tricks" in Loneoceans QCW 1.5 writeup. http://www.loneoceans.com/labs/qcw15/

[Hydron]

I should have included a couple of other measurements in my post as well, namely the primary (alone) and secondary+topload (alone) sweeps corresponding to the configuration in the previous graph. The primary is maybe not as far below the secondary frequency as is ideal, but I ran out of copper tubing about a turn earlier than expected when constructing it.

I've included a pic of the coil as-measured. It has changed a little since these sweeps (mostly due do a new topload), but I can do some new ones if it is of interest, this time with a log axis for impedance as well.

[TDAF]

Now for the inverter IGBTS
I have narrowed it down to two
IRGP50B60
And fgh60n60smd
Now irgp has very low rose and fall times but at the same time costs twice of 60n60
So, is the lower losses worth it?
Also, could yall suggest something better IGBT if any

[Hydron]

Price, low thermal impedance and past success all suggest going for the 60N60 (or the equivalent FGA60N65SMD if cheaper). FGY75N60SMD is also an option for slightly higher current (I have a thread about some very cheap ones I got from aliexpress).

[TDAF]

Price, low thermal impedance and past success all suggest going for the 60N60 (or the equivalent FGA60N65SMD if cheaper). FGY75N60SMD is also an option for slightly higher current (I have a thread about some very cheap ones I got from aliexpress).

hmm...i see

[Uspring]

@Hydron:
Your measurements all look fine for themselves. I just can't make them to fit to the coupled system measurement. Possibly its the new topload or some influence of the primary (capacitive or whatever) on your secondary alone mesurement.

[Hydron]

OK, yeah that is a possibility. I'll make some more measurements and document them better - those were from a few years back.

[TDAF]

Using the formulas off of Richie burnett''s website
My coil will have the upper pole at around 500-520khz
Doesn't that seem too high?
How will the coil ever get around to achieving upper pole operation?

Also, how can one use a startup oscillator with a ud2.7
I'm looking forward to using Steve ward''s tuning trick for QCWs

[TDAF]

So, for the MMC
Will CBB capacitors work?
I'm thinking of something like 100 caps 10 in series 10 in parallel to give about 10nf of capacitance
https://www.ebay.com/itm/10Pcs-CBB-Capacitor-100V-101-683-0-1nF-68nF-101J-683J-Pitch-5mm/192143864676?hash=item2cbcaab364:m:miP5zeN54Fp-RSicta7nMyQ
Something like these capacitors...

GUESS WHO JUST FOUND SOME DATASHEETS!!!!

looking at the datasheets even though the peak current ratings are for <100khz
the RMS ratings look quite sufficient

what do you guys think??