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Re: SIDAC Spark Substitute

Original poster: "B2" <bensonbd@xxxxxxx>

Hi Peter,

Original poster: "Peter Terren" <pterren1@xxxxxxxxxxxx>

Derek and Shaun
I am not sure what I can push the SIDAC's to and have not burnt them out yet although they get warm on a short run. Currently dumping 5.2kV 30nF cap (0.4j) a few times a second into 5 primary TC turns which is not enough for spark growth. I am not sure about how well they quench as well. Clearly they do a lot better with a high inductance coil such as an ignition coil.

They may also be placed in parallel the same way as spark gaps by using resistors or inductors. Big RF beads or toroids may slow them down enough to force current sharing with parallel strings. A string of 1N5408 diodes (10) could be used to crowbar the pulse to prevent ringing. I built a DCTC that way. It ran at 50 KHz. Sparks were almost twice as long as the uncrobarred version, but they weren't as bright. I have been told by many that the internal capacitance of the diodes prevents them from doing this. I don't disagree that some solid state devices have large internal self capacitance. I also don't disagree that the diodes leak at higher frequencies from their internal self capacitance. The overall energy wasted in the primary switching circuit is much less, overall. The SIDAC's will leak at high frequencies, for sure. Putting strings in parallel will cause the energy loss to be dissipated over a much larger area. Putting diode strings across the SIDAC's will reduce the energy wasting ringing. Good luck!

B2