Wire and resonant capacitor sizing in LoneOcean's QCW

[Unrealeous]

I've been studying loneoceans QCW design, which is probably the most well documented QCW's on the internet and I have a few questions.  Not actually related to the QCW itself but to some of the decisions he's made with components.

The design was originally to get 100Amps through the primary, but it looks like he eventually is getting closer to 200 amps.

So here are my questions.

Q1.  He's using AWG14 wire in his buck convert inductor.

Clearly 200 amps is well above the Max steady state 5.9Amps for the wire.

So I guess I'm asking how does one calculate what the minimum wire specification could be used? 

I am making the assumption that the buck inductor current will roughly equal the primary current.

Then I'm guessing that since a QCW is going to be pulsed, on for 20ms, and off several hundred milli seconds, is it just a case of taking the rated current, dividing by the maximum current to find the max duty cycle?  5.9/200 = 2.9% (I'm ignoring the fact that the current ramps linearly, so you could double that figure).

Q2.  Same current rating again but this time for the resonant capacity.  He's using a Mica 12.8nF that is rated for 40A rms.

Again, seems well under his 200A max goal. 

This one I really don't have a feel for how much pulsed current this capacitor could handle.  Is there a way to work this out.  I'd be very happy to be educated or pointed in the right direction.

Thanks

[klugesmith]

The max current values in your wire table are ridiculously conservative for most applications,
with possible exception of densely packed transformer windings. 
It's all about the insulation temperature rating and the thermal resistance where the wire is placed.
US national electrical code allows AWG14 nonmetallic cable ("Romex") in circuits with 15 A overcurrent protection, which could properly allow 20 A for many minutes.  It would probably be a violation if a buried conduit were tightly packed with AWG14 wires all carrying 15 amps.

[edit] The max current values in your table appear to be about 3 amps per square millimeter.   That's a conservative limit for magnet wire densely packed in a power transformer winding.   Without active cooling the winding will eventually get pretty hot, but the insulation is generally rated for temperatures above 100 degrees C.

[Unrealeous]

Thanks Klugesmith, I'm Australian so not as familiar with the AWG standards, and the first google result gave me that table which I now see is very conservative.  I've since found that depending on the insulation AWG can be good for up to 20 amps (NEC Table 310.15(B)(16) for copper conductors with 75°C insulation)- so I appreciate your input.

Building telsla coils involves pushing components past their rated limits as we are running fairly low duty cycles, and it seems by trial and error that coilers have come up with good rules of thumb for how far things can be pushed.

Generalising: we can push the current limits, but careful going over the voltage ratings...

So in an attempt to answer Q2: if its rated for 40A RMS continuous, doing 200A peak at 5% duty cycle ok.  Loneocean's design works so clearly this is true.

Although RMS current rating not always specified on capacitor datasheets...


Edit: Maybe I should be more specific and ask the question i really want answered.  I am looking for a suitable substitute capacitor for loneoceans design.

Would something like 2x DAWNCAP DTR 0.022UF 6000VDC 3000VAC 60A in 2S configuration be suitable replacement for his Mica capacitor (Mica 12.8nF)
https://www.aliexpress.com/item/1005005553272342.html

[Mads Barnkob]

These current ratings are meant for house installations and machine construction, hence why they are very conservative. This is for 24/7 use in many many years, without any risk of fire. There is even reduction factors for higher temperature, grouping and installation method. So the current rating you see in the table, is often much lower when calculated for a installation.

The AWG tables and the European EN60204-1 pretty much states the same conditions and sizes, I compare them here: https://kaizerpowerelectronics.dk/theory/wire-size-table/

Intermittent use, good air flow and possible forced air cooling will help ALOT on the current carrying capability of any conductor.