Re: [TCML] Terry Filter Caps

[bartb <bartb@xxxxxxxxxxxxxxxx>]

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)
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>   
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla