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Re: Cap Failure Pictures

Hello All,
Don Froula <froula-at-cig.mot-dot-com> wrote:
> Pictures of my failed Condenser Products cap from the first group buy >are
now available for viewing at:
> 
>         http://homepage.interaccess-dot-com/~dfroula/tesla/tesla.html
> 
> A text description of the failure is included as well.
> 
        The pictures are quite informative.  Thanks for posting them.  As an
owner of one of the group purchase .025 Condenser Products capacitors, I
have been a bit concerned about their reliability after hearing of three
reported failures of CP products.  I have hammered mine pretty hard, but at
a relatively low 9-10 kV, using no more than about 1.3 kVA maximum power.
So far, it has performed admirably, and remains intact.
        Nonetheless, I was curious about how much air is inside and the
general construction of the unit so I hauled it to work Friday and shot a
couple X-rays of it to have a look inside.  There is a relatively small air
bubble inside which does not appear to be a source of concern, based on its
small size.  Since there is no venting to the outside, you would expect to
find a small air bubble to handle the expansion/compression of materials
inside as the temperature changes.
        There appear to be four sub-assemblies inside, each of which looks
like it is constructed of two metal windings, making either four or
(probably) eight total capacitors inside which are hooked in series via some
material with higher x-ray absorbing properties (probably tin or an alloy of
tin).  The ribbons/wires which connect the subassemblies together appear to
have shed a few metallic particles, which have drifted away from the
sub-assembly end plates.  As a result, there are a couple particles which
are now located along the periphery of the sub-assemblies.  The particles
appear to be part of the ribbons or solder particles, as they are quite a
bit more absorbing of x-rays than the sub-assemblies.  I was unable to
determine whether the particles are free-floating in the oil, but they are
definitely along the outside of the sub-assemblies and/or between the
sub-assemblies, near the PVC casing.  One of the particles is quite jagged,
as are some of the solder connections between the coils.  My guess is that
these pointy little fragments are the culprits in the catastropic failures
of these units.  Probably, there has been an electric field build-up near
these critters, and if they happen to be in the wrong place at the wrong
time, arcing results, and the lack of venting causes the end caps to blow. 
        I took my cap home, hooked it up (with end caps in the appropriate
direction!) and fired up my little magnifier with no hitches Friday evening
using 10 kV.  I think I'll build an oil reservoir just in case, however.  
    
Regards,
Mark S. Rzeszotarski, Ph.D. (still dinking with math)