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
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