Lau, Gary wrote:
Thank you Jim for a much-needed sanity check! There is an awful lot of advice out there suggesting that massive ground wires are needed, probably driven from a lower inductance (?) perspective than a current carrying one. I'm curious about your report of killing an NST in a coil that was not properly grounded - I've not heard of such a failure mode before. It's clear that without a proper ground, that the RF return path will occur _through_ the NST and into the mains wiring. Do you know just what it was in the NST that failed? Primary to core insulation?
To be honest, I haven't done any post mortem on it. It was an old 9/30 that I was using in a small coil. I forgot to hook up the bottom of the secondary to anything. I was fooling around with the coil and noticed that the sparks were very different, lots of racing sparks, sparks from the powercord to where it passed over a plug strip and then the coil just died (as in no HV into the gap).. So I pulled the NST out, saw it had no output and threw it in the "look at it when I get a chance" box (where it has been for >10years I now realize). Put in a new NST, reconnected everything (incuding the bottom of the secondary this time) and everything worked.
This is the ONLY time I've had a NST fail in tesla coil duty, and for all I knew, it was that NSTs time to go anyway. But I'm pretty sure that the RF propagating back through to the power line and greenwire ground didn't help.
Commercial EMI filters are actually not very good at attenuating the relatively low resonant frequencies that most coils operate at. Their main application is to attenuate much higher frequencies. This isn't to say that EMI filters are worthless, as TC's generate a lot of harmonics; just not what many of us think they are. Regards, Gary Lau MA, USA
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla