Re: Maxwell AC vs. DC ratings & failure modes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Scott,

I will also be interested in what truly breaks these capacitors.  I think 
we can rule out current ;-))  But that leaves us with pure over voltage or 
dielectric failure do to ionization.  I find it hard to believe that 
ionization would do it and 35kV is pretty high for a breakdown voltage.  I 
just don't see why these super robust commercial caps pop like pop-corn 
when hooked to a simple NST...  I guess we would also have to consider 
mechanical stress, but these are multi kamp caps...

Cheers,

         Terry

At 03:49 PM 4/4/2004, you wrote:
>Mike -
>
>Thanks for the additional info on the failed Maxwell capacitors. As I
>suspected, there were no measurements made on the actual operating voltage
>when the caps failed.
>
>Just because the system was connected to a 15 KV NST does NOT mean that the
>voltage across the capacitor was 15 KV; it may have actually been 2X or 3X
>or higher, depending on resonance effects, safety gaps, etc, etc. Please
>post the results of your failure analysis when you open up the capacitors.
>If you like, I'll pay shipping costs for you to send one of the failed caps
>to me and I'll perform an intensive failure analysis in my lab at work, and
>post the photomicrographs & findings at hot-streamer-dot-com for everyone to
>review. We've seen several failure analyses of MMC caps that died in Tesla
>coil service, but nothing on a commercial pulse cap that died under similar
>conditions.
>
>As for the Tesla coil driven by the 90 KV X-ray transformer, a posting to
>this list from Mike.Marcum-at-zoomtown-dot-com dated Sat, 04 Oct 2003
>05:09:29 -0600 went into great detail describing the system, with the X-ray
>transformer cooled by a car radiator & pump system, driving a giant MMC
>array of five-hundred (!!!) Cornell-Dubilier 943 capacitors, with the whole
>system drawing 24KVA (!!!!) and being capable of operation at this power
>level for a period of 10 minutes before "the neighborhood browns out". This
>posting is archived at www.pupman-dot-com.
>
>Likewise, the claim of a 50 KVA Jacob's ladder running in your backyard (two
>34.5 KV, 50 KVA pole pigs):
>
>"Don't know what the actual power draw was, but it was popping 800A worth of
>breakers (!!!!) in 5 seconds or so (made the drop wire from the pole quite
>warm in the process). The arc spread over 17 feet before the breakers popped
>(which was over 4" thick and bright as a welder". This also is archived at
>Pupman-dot-com, posted by Mike Marcum -at- zoomtown-dot-com, on Sun, 23 Nov 2003
>22:04:59 -0700.
>
>Are there somehow TWO different Mike Marcums -at- zoomtown-dot-com?  Could there
>somehow be an "imposter" posting incredible claims under your name?
>
>Regards,
>Scott Hanson
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Sunday, April 04, 2004 1:48 PM
>Subject: RE: Maxwell AC vs. DC ratings & failure modes
>
>
> > Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
> >
> > Some information about the operating voltage might be inferred if you
> > could supply just a few more details.  What size NST was used (voltage
> > AND current), what size cap was used (I assume just the single
> > .03uf/35kV), gap type (sync/async), and safety gap/MOV used?
> >..........