Killed An MMC -at- last
i have been slowly rampng up the abuse on my small coil's mmc.
Today one of the caps failed. From what i can tell it was an over voltage
failiure as there is a large defect in the poly and the explosion when the
cap died was big enough to blow the side of it out and set fire to the cap
next to it. The cap was pretty hot even about 2-3mins after the failiure but
this was probably because of the fire rather than over current. When it
failed I was running a 5mm gap on a 6/60 neon with 30nF of total capacitance.
The caps are philips 378 series 1600V 47nF. These are definitely not good
mmc caps as they have a very low dv/dt rating of 900v/us and rather high esr
(Equivalent Series Resistance - basically impeadance of the cap) but they
were what I bought and they weren't too expensive. They were in 6 parallel
strings of 10. I think they chose now to fail because I have at last
actually set my system up for mains reso charging and therefore the peak
voltage will be alot higher than in my previous setup. Oddly although I had
widened the gap about 1mm further than ever before and doubled the cap size
the sparks increased by only about 4" from 11" to 15" ?
Commiting GCH in GB
GCH (Grievous Capacitor Harm)