Re: What caused capacitor failure?

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

Original poster: "R Heidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

on 10/22/01 1:09 AM, Tesla list at tesla-at-pupman-dot-com wrote:

> Original poster: "Brett Error by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <bretterror-at-hotmail-dot-com>
> 
> Thanks to all on this list.  You've been tremendously helpful, and this
> evening I finally got some sparkage as the fruits of my labor.  Worked
> great, and even my wife was awed.  She finally understood why all the
> effort.
> 
> Unfortunately, I've already had a capacitor failure.  Seemingly relevant
> specs of the coil:
> 
> 12kV 60mA NST
> MMC Built almost identically to the one Terry describes:
> http://users.better-dot-org/tfritz/site/MMCinfo/MMC.html
> 
> I used the identical capacitors described ordered from DigiKey.  However, I
> only used eight in series as I only needed to support 12kV.  I built three
> strings, but only used two of them in parallel for a total capacitance of
> .014 microFarads (the transformer matches to .013 microFarads).
> 
> I have a RQ-style cylinder spark gap with 10 .28 inch gaps in series.
> 
> She ran beautifully for probably 10 minutes of total run time during the
> course of several hours (15-second or so at a time).  However, shortly after
> lighting her up the last time one of the capacitors split and caught fire.
> I immediately shut down the coil.  When I examined the capacitor bank more
> closely I found that ALL the capacitors have suffered stress.  They have all
> at least cracked their outer coverings, many of them have completely broken
> away chunks exposing the foil inside.  Unfortunately, I didn't check the
> caps as I went to see if they were gradually failing, or if this was an all
> at once, catastrophic thing.  But based on how they look I would guess they
> were gradually failing.
> 
> Right after failure I checked the other caps and they were not hot... I
> don't think the failure was from heat break down.  Instead, from the look of
> the other capacitors, it looks like they actually sort of blew themselves
> up.
> 
> Any ideas what would cause this?  My first guess would be too much voltage
> and they really did blow themselves up.  However, the caps are rated at 1600
> VDC each, so with 8 in series I should be able to handle 12.8 kV.
> 
> How can I prevent this problem in the future?  Needless to say, that was an
> awfully expensive 10 minutes (although immensely satisfying).  I'd like to
> figure out what I can do to prevent this failure before trying it again.
> 
> Thanks in advance for your help.
> 
> Brett
> 
> 
> 
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> 
 Brent; 12 kv x 1.414= 16.9 kv peak ac.  If your peak voltage is over the dc
v of your capacitors you didnt have a chance.
    Robert H