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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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