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Re: [TCML] Terry Filter Caps
I'm not sure how many "Adams" there are on the list, but this post was from Phil and Gary. But I don't use any filters other than EMI on my pig coil.
Adam
--- On Sun, 8/24/08, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
> From: bartb <bartb@xxxxxxxxxxxxxxxx>
> Subject: Re: [TCML] Terry Filter Caps
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Sunday, August 24, 2008, 10:38 PM
> Hi Adam,
>
> Did I get this right? Are you running a Terry Filter with a
> pig?
> Just curious about that. I personally don't use such a
> filter with a pig
> transformer. Only for NST's. Not that it hurts, but
> I'm not sure it's
> necessary. NST's are voltage fragile. Transients are
> part of that. The
> filter helps some in that department.
>
> Regardless, in this discussion, people should remember the
> MOV's across
> each cap/resistor circuit within the Terry filter. As long
> as the cap is
> of adequate voltage and the MOV's are designed for the
> "transformer",
> then there is plenty of protection across each individual
> RC section
> (beyond the cap or resistor ratings). But with a good
> design, those are
> last resort.
>
> Best regards,
> Bart
>
> FIFTYGUY@xxxxxxx wrote:
> >
> >
> > In a message dated 8/24/08 5:22:23 P.M. Eastern
> Daylight Time,
> > Gary.Lau@xxxxxx writes:
> >
> >
> >> I don't believe that caps used in a Terry
> filter need to follow the same
> >>
> > criteria for being "good" as
> >
> >> caps used for a tank capacitor.
> >>
> >
> > Certainly the RMS current rating doesn't need
> to be as high - unless you
> > are running the coil unattended for long periods of
> time. If something goes
> > wrong where the Teryy Filter starts to conduct
> continuously, weaker caps
> > might get hot quickly. But most of us turn off the TC
> when the streamers suddenly
> > disappear...
> >
> >
> >> The current in Terry filter caps is limited by
> those big 1K resistors, and
> >>
> > is very small compared with >what a tank cap sees.
>
> >
> > Yes, true. In fact I had several arcs at my
> safety gap last night with
> > my pig, but the sparks were comparatively thin (like
> off a stun gun). I've got
> > my safety gap closer to the pig than the Terry Filter
> resistors, unlike the
> > usual configuration. No problem with the safety gap
> extinguishing.
> > But consider that through those same resistors we
> intentionally push a
> > few kVA of high voltage with only a small percentage
> lost. The transients we
> > are trying to suppress might be of even higher
> voltage. So no problem for them
> > to get back through those resistors, even if they are
> 1K. In fact, if the
> > transients couldn't get through the resistors,
> there would be no point in
> > having the Terry caps!
> >
> >
> >> Typical values for ESR and ESL in any kind
> >> of cap should present no problem in a Terry filter
> application.
> >>
> >
> > Once the transients get through the resistors, we
> want to shunt that
> > current to ground, That's where the low ESR and
> inductance of the Terry caps
> > becomes important.
> > That's why our MMC caps are commonly used in
> "normal" electronics in
> > snubber duty. It's also well-known that for
> transient suppression, keeping the
> > suppressor wiring low impedance is very important.
> >
> >
> >> I have used ceramic doorknob caps, and even
> ceramic disc caps, provided
> >>
> > they have a suitable
> >
> >> voltage rating, are fine.
> >>
> >
> >
> > Well, if they work for you, I guess they're
> "fine" for you! But
> > everybody's setup is going to be different. Some
> people here have done a *lot* of
> > coiling without ever using a filter, and have had
> little or no problems that
> > they are aware of. Others have destroyed ancillary
> equipment the first time
> > they've powered up their TC! I'm personally
> pretty rough on equipment, so I try
> > to make up for my shortcomings with as much protection
> as I can afford. And to
> > me the price difference between "ok" Terry
> Filter caps and "pretty darn
> > good" ones is very cheap insurance. I'd also
> rather blow all of those pretty
> > little caps to smithereens than have to replace my
> neighbor's PC, for example.
> > I'll certainly agree that almost *any* cap
> even close in ratings will
> > work to *some* degree for Terry Filters. But using the
> good stuff is cheap
> > insurance... isn't that what the Terry Filter is
> about in the first place?
> >
> >
> > -Phil LaBudde
> > Center for the Advanced Study of Ballistic
> Improbabilities
> >
> >
> >
> > **************It's only a deal if it's where
> you want to go. Find your travel
> > deal here.
> >
> (http://information.travel.aol.com/deals?ncid=aoltrv00050000000047)
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> >
> >
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