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

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

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>


Chris,

Yes, and 3 strings of 9 would be even more robust and would give you the
same capacitance as your 2 strings of 6.  It's a good investment - worth the
extra cost in peace of mind and MMC longevity.
--Steve Young

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, November 27, 2002 8:40 PM
Subject: Re: Dead MMC. was: AAAA! My coil...


 >
 > 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
 >
 >