Re: [TCML] SISG heating at high freqencies

["Peter Terren" <pterren@xxxxxxxxxxxx>]

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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