Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx> Hi, At 07:03 PM 12/15/2005, you wrote:
I will publically applogize for hurting the feelings of good ol' Matt. My point is this (and lets end it here): if you want your coil(s) to last FOREVER, Forget about homemade capacitors. Any new comer that has the desire for a Quality coil should build an MMC! SIMPLE AS THAT...
MMC really don't last "forever". See: http://hot-streamer.com/temp/CD942C20P15K-MMC-Capacitor-Lifetest.pdfBecause we run them at 2000VAC when they should only be run at 630VAC, the plates inside get eaten by ionization and burn up in say 75 - 100 hours.
One could use many more caps and run each at ~600VAC to get to say 100,000 hours, but then the cost goes way up.
Most of use are perfectly happy with a say 75 hour life, if you need to run longer, then the normal MMC should be changed or another type of caps used.
Homemade caps have a similar ionization problem due to their single poly layer. Even in oil, there is significant ionization damage when we are talking many hours of use. Homemade caps are each too unique to say much about how long they will last. Dave's have been going about 11+ years, but I am not sure how much actual run time that is.
Commercial caps (but NOT "pulsed" type caps) will actually be made with a number of "cells" in series to over come this in their oil filled caps. That's why they can get $500 - $1000 for them. I think DC Cox recently mentioned his fully rated AC Tesla coil duty caps (the kind that will last "forever") ran $1000 each in QTY of ten!! So his ten caps probably cost more than ALL of our MMCs combined!!
Cheers,
Terry