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[TCML] Non-DR SSTC primary - interesting facts



Well, upon an attempt of further civilizing my flower-pot primary I removed a turn (getting 6 turns instead of 7) and blew two fets (was a pretty stupid idea - even the primary itself lost ~25% of it's inductance, first blow on the finished construct btw) - and the interesting part is - the spark almost didn't grow (was up to 60cm - remained the same). Of course I put the turn back and replaced the fets (working fine again, same spark - and the heating of the bridge is very subtle btw, even with my really bad cooling), but it led to some interesting thoughts, also based on my older research. The idea is - you have a fixed-height primary with a significant number of turns and start reducing that number one by one, keeping the height constant. At first you get a low transformation coefficient and high inductance, thus the power is too low. As you remove the turns, the transformation coefficient gets higher and therefore the power transfer into the secondary increases. That's good, but - you slowly increase the reflected power by doing that, therefore the SWR gets worse and worse, making LESS power supplied into the secondary. The question is - is the resulting power supplied into the resonator rising all the time, or there's a peak after which you start making the coil be able to transfer less power again? By the way (didn't test that on my new coil, actually as far as it's working well and never blows I'm not going to change much - 60cm on a bps up to around 30 with a pretty high pulse length feels like a proper result for a bridge of 30a fets ;) - and the secondary heats up pretty much anyway) the tests on the previous version of this coil (there was no feedback at the point, and the secondary was much smaller and ran at ~300kHz instead of the present ~150) showed that the primary height (meaning not how high the top turn is, but the distance between the top and the bottom turns - eg the top turn remained at ~1/4th of the secondary, but I tried both spreading the primary to the bottom of the secondary and winding it tight) doesn't affect much as long as the winding remains close to the secondary.. So, is there a point of an "optimal" primary, at which further turn reduction has only negative effects?
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