Re: Necessity of NST Protection Filters and Safety Gaps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "June Heidlebaugh" <rheidlebaugh-at-desertgate-dot-com> 

The second for the use of the 1K wire wound resistor is the inductance of
the coil/resistor to disconnect the NST from the load when the spark gap
fires so you do not have a dead short across your NST. My resistors provide
275 uH of inductance as a RF choke to disconnect the current spike. That is
much more than the 3 uSec disconnect required to protect the NST.
    Robert   H
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, January 16, 2004 6:03 PM
Subject: Re: Necessity of NST Protection Filters and Safety Gaps


 > Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 >
 > Basically you just want a HV RC filter.  500pF and 1k R works out well to
 > most NST sizes.  Smaller NSTs should use lower value resistors - don't
want
 > to waste too much power in the resistors on a small coil.  The "Terry
 > Filter" is a solid design using HV PP film capacitors identical to the MMC
 > capacitors (only smaller in value) and a "big" wirewound enameled power
 > resistor (25-50W is big when you're used to 1/2W or less).  And to throw
in
 > some extra protection, some MOVs are added to clip any voltage spikes that
 > made their way through the filter.
 >
 > I built one for my first coil, and I think was one of the first to ever
 > destroy one....  I guess I forgot to set the safety gaps
 > properly....  oops....  The MOVs are somewhat pricey and are only there as
 > "one last line of defense" so I have no problems recommending that the
 > budget concious omit them.  But I will say that replacing $20 in MOVs was
a
 > lot easier than replacing 2 NSTs.  ;)
 >
 > http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg
 >
 > Although *I* may use them, The Geek Group has never used one, and hasn't
 > had a problem since we learned to properly set the safety gaps before
every
 > run (that was before even *I* was a member).
 >
 > Cheers.
 >
 > Mark Broker
 > Chief Engineer, The Geek Group
 >
 >
 >
 > On Fri, 16 Jan 2004 12:01:26 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:
 >
 > >Original poster: "Luke" <Bluu-at-cox-dot-net> That's good to hear bout your
NST's
 > >not burning up.  That is something I
 > >will have to tackle soon.
 > >
 > >Do I want a protection circuit?
 > >If so what is the best style and why?
 > >And if so how do I choose my values for the components and why?
 > >
 > >If you feel like giving any input ill gladly check it out.
 > >If not I may be posting some questions later after I do a little
 > >reading.
 > >
 > >
 > >Luke Galyan
 > >Bluu-at-cox-dot-net
 >
 >
 >