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Re: Leaky capacitor woes.


From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Saturday, November 22, 1997 2:52 PM
To: 	Tesla List
Subject: 	Re: Leaky capacitor woes.

Tesla List wrote:
> 
> From:   Adam[SMTP:absmith-at-tiac-dot-net]
> Sent:   Thursday, November 20, 1997 11:03 PM
> To:     tesla list
> Subject:        Leaky capacitor woes.
> 
> I have built a flat plate cap, which at first seemed great, but now
> demonstrates a great oil leakage problem.  The cap is made from LDPE and
> Aluminum plates, and it is housed in a rubbermaid polypropylene storage
> box.  I "sealed" the box by hot-gluing a plexiglass panel over the top.
> 
> This cap leaks oil something fierce.  The problem is I cannot figure out
> exactly how the oil is getting out.  I have a clean dry cap, and then I
> come back 4 hours later and it is sitting in a pool of oil.  The oil is
> Exxon Univolt N61.  I have already checked for leaks, and have found that
> the hot glue does not adhere at all with the plexiglas, allowing oil to
> flow freely out through the junction if I tip the container so that the
> oil is in direct contact with this seam.  However, there is normally 1"
> of air space above the top of the oil and below the seam.  So, I have two
> theories:
> 
> 1.  The oil is evaporating and condensing on the plexiglas (observed) and
> must then be "rolling" along the plexiglas surface to the hot glue seam,
> where it freely leaks out thanks to capillary action.
> 
> 2.  The oil is passing through the polypropylene container itself.
> 
> Evidence suggests theory #1, but I have not ruled out the second theory,
> as the capacitor seems to be oily all over.
> 
> Any ideas?
> 
> -Adam
> 
<SNIP>

Adam,

from the quantity of oil pooling, it sounds like you might either have a
porous or cracked container. Since you seem to be seeing the oil all
over the outside surface, I'd suspect the former, although this is the
first time I've heard of problems with porous PP. Mineral oil based
transformer oil is really not very volatile at room temperature - it's
more like a light machine oil. Although I'm only directly familiar with
Shell Diala-X, Exxon Univolt should have similar properties, since both
are naphthenic-based mineral oils. 

Try using a different material container. I've had a couple of my caps
in large trashcan-type containers from Rubbermaid that are made from
LDPE with a HDPE top - no leaks or seepage in almost 2 years. Don't use
polystyrene - it softens and dissolves with time. Also, polycarbonate
may tend to be a bit brittle if you accidently knock into it. LDPE,
HDPE, PP, PVC, and even a custom-made Plexiglass (PMMA) box should all
work. Polypropylene SHOULD make for a great container... this is a real
puzzler!

Safe nonleak cappin' to you, Adam!

-- Bert --