Re: Dead MMC. was: AAAA! My coil...

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

Original poster: "Chris Roberts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <quezacotl_14000000000000-at-yahoo-dot-com>


So does that mean the geek group MMC ratings are off? If so, would 3 
strings of 8 caps work? That approaches the original value and should have 
a higher voltage rating. Sigh- thats quite a few more capacitors (plus the 
dead one I have to replace). Almost makes me want to go back to bottle caps 
(shudders at the thought).

  Tesla list <tesla-at-pupman-dot-com> wrote:
>Original poster: "Barton B. Anderson by way of Terry Fritz "
>
>Hi Chris,
>
> From your description, it sounds like the cap was arcing internally and
>overvolting the resistors. Once the last resistor was removed, the cap
>itself went into a runaway condition and failed from the same internal
>arcing and all the fun dynamics that goes along with that. My guess is the
>cap was originally damaged due to being overvolted by the transformer. The
>NST at 9kV(rms) has a Vp of 12.7 kV. The cap bank was rated at 12kVp, so
>you were definitely on the edge or slightly over.
>
>The rms current looks good and is the area where you will see reliability
>ratings (it is also the typical area of concern), but the cap voltage must
>also be considered. Maybe more emphasis on derating the cap should be
>rolled into cap reliabil! ity. Often it's not and just assumed the user
>should know this. Derating at 2.5 x Vp is a good rule of thumb.
>
>Take care,
>Bart


-Chris

"Learn from the mistakes of others. You won't live long enough to make all 
of them yourself."-unknown



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