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Homemade Capacitor death.


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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Tuesday, February 17, 1998 8:45 AM
To:  Tesla List
Subject:  Re: Homemade Capacitor death.

Tesla List wrote:
> 
> ----------
> From:  David Huffman [SMTP:huffman-at-FNAL.GOV]
> Sent:  Monday, February 16, 1998 9:55 AM
> To:  Tesla List
> Subject:  Homemade Capacitor death.
> 
> Hello Group,
> I have to confess my own ignorance to maybe help someone else. I fired my 8"
> coil last night for the first time with my homemade caps. After tuning I
> began to crank to variac up and was happy to see the sparks grow to about
> 30". It seemed pretty good for just 12KV -at-60 ma input.  It only lasted about
> 10-15sec. however before failing. I had made 3 identical caps at about 80nF
> each and was running them in series. The caps started out flat. The layering
> was foil 5-mils paper, 8-mils poly, 3-mils paper, 8-mils poly, 5-mils paper
> and foil. The error occurred when I folded the flat layers up to fit them in
> a PVC pipe. I didn't recognize that the outer layer of foil of one electrode
> was separated from the other electrode by a single paper width. The
> beginning and ending stack should have had several layers of insulation.
> I still can't believe I did this three times and never thought about what
> was going on!
> I took a bath in transformer oil shortly after the failure and repaired one
> of the units. The big problem is trying to fit it back in the container
> since it has swelled up with oil.
> Learning what to do by doing all the things not to do.
> Dave Huffman

Dave,

Congrats on first light with the new coil. Bummer about the cap failures
though! Sounds like you were getting very good performance off them
before they failed. Other than the poly swelling, it sounds like they
should be fairly easy to repair (albeit messy!)...

Speaking about messy, I also had a capacitor failure the evening of Feb
8th when Jim Fisher and Dave Flinn were over. Tedd Payne was over a bit
earlier - I was interested in some of the plasma globes/gas bottles he
had. We'd shrunk a number of coins and crushed a bunch of cans
successfully. Anyways, during one of the firings one of the large caps
in the quarter shrinker ruptured the case, spilling a couple gallons of
blackish oil on by indoor-outdoor carpeting! After autopsying it, I
found that it had a manufacturing defect which caused the ground bus to
begin detaching from the individual modules. 

Unbeknownst to me, each "pop" resulted in another 1-2 modules being
disconnected. The internal arcing then created the black oil, aluminum
end-foil debris, plus a shock wave which weakenned the NEXT connection.
Finally, the pressure apparently was sufficient to crack the weld in a
corner of the case so that there was a split about 10" long. The ground
bus was literally being blown off the ends of the cap modules. When it
failed it only measured 39 uF. The "hot" side of the cap was perfectly
fine, as was the partner capacitor. I've added a third cap to the system
and am now monitoring charge times plus bank capacitance to detect any
leakage/capacitance changes to thwart this from occuring again.

BTW, I've got some 12 KV 60 MA transformers if you're interested. Also,
what did you decide to do re: the transmission line problem at work?

See ya!

-- Bert --