I was playing with a 4 segment SISG with a 4 inch coil about 8 inches tall
and 0.06 uF cap.
Primary of 2 turns from a ballasted MOT (half wave rectified) and no
toroid. Frequency would have been quite high >2-300kHz or even more.
I was just messing around with the threshold voltages for curiosity and
was using 3 of the 4 segments to get 1 inch sparks.
I was quite surprised to find that the SIDAC's were scorching hot and the
IGBT's were uncomfortably hot, particularly one of them after a very short
run. Considering that these have been used by others on a pole pig with
only mild heating, that surprised me.
It sounds like they had some frequency dependent problem because the SISG
works OK (ie cold) with more primary inductance/capacitance. Beats me why
the SIDAC's were getting hot though. Perhaps the IGBT's weren't turning on
fast or fully so the SIDAC's spend more of the time conducting throughout
the cycle relatively. Perhaps a lower gate resistor may have helped (I was
using 100 ohms).
I was planning to use a smaller 4 stage SISG for a demo mini coil but
would have to sort out the frequency issues first.
Peter
www.tesladownunder.com