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



Hi Scott,

Sounds like the caps had excess voltage they couldn't handle. The reason is the failure mode. One blows, then the chain reaction starts. As soon as one is gone, the rest then see a few hundred volts more per cap. Did you use 1600V caps? If so, were these the ones listed by Terry (P10501)? If not, what did you use?

Again, the failure sounds like punch through and not current. If true, the fix is the cap standoff voltage. A 9/30 "SHOULD NOT" have killed the caps if they are the P10501's. Unlike the MOV's where the quantity is different for various NST output voltages, the caps don't change. Their quantity remains the same for all NST's up to 15kV. The standoff voltage is 9600 volts per each side of the NST to ground, so no way the 9kV NST across the whole filter should have blown a cap.

Bart

Scott wrote:
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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