Re: Capacitor Explosion

>From MALCOLM-at-directorate.wnp.ac.nzMon Jul  1 22:15:05 1996
>Date: Tue, 2 Jul 1996 08:02:56 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: Re: Capacitor Explosion

>Hi all,
>       I was disappointed to hear about CP's treatment of your 
>complaint Richard. Not what I would expect from a top quality company.
>They shouldn't have been surprized that a small select community 
>should know about the woes of one of its members regarding one of 
>their caps. Not too many people indulge in making lightning in the 
>     Regarding the oil and cap laying on its side - what the heck do 
>they expect? I noticed when I first got mine that I could hear oil 
>sloshing around in side. I had to assume that was OK but I now have 
>my doubts. Sloshing sounds = air inside. I haven't decided exactly 
>what course of action I should take but I'm thinking about putting
>a plug in the end and topping the thing up properly (stuff the 
>     The only comfort I have received from all this is that at least 
>the dielectric seems sound enough. I'm amazed that, given the size of 
>the external studs, the internal interconnects sound as if they're 
>entirely inadequate. Perhaps they haven't heard of Kirchoff's Law.
>     Not very satisfactory!

Malcolm, All,

I believe that a small void, like an air bubble, but which may in 
fact be a vacuum space when the cap is sealed at the factory, is 
purposely left in the cap to act as an expansion space to allow for 
the differential expansion of the oil and the case over the expected 
storage and running temperature range of the capacitor.  I do not 
advise opening up the capacitor and topping it up and then resealing 
the hole, UNLESS you use a flexible plastic or metal external bellows as your 
sealing plug.

Besides, rotating the capacitor before use shouldn't be a problem for you in New
Zealand.  Didn't the capacitor get turned almost 180 degrees as it was shipped to
you from the USA?  Ha. Ha.

Scott Meyer's excellent post just suggested safety shields for the 
capacitor (among some excellent other safety ideas).  I think he's onto a good
train of thought!  Perhaps the cylindrical CP capacitor could be installed inside
a larger diameter PVC pipe section with end caps welded on as a containment
housing.  If you were to fill the void between the two tubes with styrofoam
shipping pellets or something,  that might work.  Also leaving a breathing hole 
(1/4 inch dia?) in the outer containment vessel would act as a slow pressure
release port, dissipating the pressure energy shock if the capacitor went into 
grenade mode.  You'd have to have a perforated breathing vent tube so 
that any number of styrofoam pellets could not conspire to seal off 
the vent in the case of internal overpressure.

Food for thought.

Happy (and safe) Coiling!, rwstephens