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Re: [TCML] Terry Filter Caps Suffering From Early Death



Scott

When I first had my coil going I had Terry filter cap failures. Coil performance did not reduce but I suspected the filter was not doing what it should. Once one went others followed. Some caps swelled, some burst through a small hole with foul-smelling oozing plastic stuff. I though I had appropriate caps, given Terry's recomendation. We don't have digikey here in Aus but from RS components I bought Epcos Metalised Polypropylene Film, MKP, 10%, 1600VDC, 500VAC, RM15mm, 3.3nF caps. A bit more searching in the catalogue and I then though I should buy some Evox/Rifa *high frequency*, pulse, polypropylene film, 3.3nF, 1600V capacitors. No problems since and (I assume) the Terry filter is working fine and doing what it should. I hope this is of some use to you. If not then check the spacing of your safety gap. Also I have heard that if the bleed resistors are too close then they can arc across to them. Mine have just 3-4mm space.

Dave Nelson
----- Original Message ----- From: "Scott" <doxiescott@xxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, June 16, 2008 6:06 AM
Subject: [TCML] Terry Filter Caps Suffering From Early Death


Hello Everyone,

As I work on my second coil, it has come time to install the NST
protection.  One very odd problem I noticed with my last Tesla Coil, a
9/30, is that the caps on the Terry Filter would periodically blow out
for no apparent reason.  Even with a RF ground directly in the Earth
and no sings of arcing through the filter (with the exception of the
safety gap), the caps at the end of the strings would die for no
reason.

The filter is grounded with a single 10awg wire 1 foot long going into
a 2 foot long 6awg car battery cable going directly to my grounding
post.  It's positioned 2 feet away from the NST.  When a cap blows
out, it seems to have little effect on the coil performance, but as
soon as one goes, the ones behind it blow up very quickly.

Now the second coil is a 15/60, 3 times the power of first, and I
would like to get this issue resolved.  Does anyone have a possible
answer to why this is happening?  Is there a more robust alternative
to the caps recommended in the Terry Filter recipe:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P10501-ND

Thanks for any help with this problem.  I'm sure the Filter has done a
great job protecting the coil, its just annoying replacing these
little 60 cent caps every 5 minutes of run time or so.



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