Re: Why does running an NST on an async gap kill it?

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

Original poster: "Dr. Resonance by way of Terry Fritz <teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>


The "Terry-filter" does a great job of protecting the HV side of NST.  On
the primary side, in addition to the usual RFC line filter, we add a "hash
filter" which consists of a 7 inch long x 2 inch dia. PVC water pipe.  The
pipe is filled with 6 x 1/4-20 steel bolts or steel welding rod.  Silicone
the steel in place leaving 1/2 inch on each end to drill a mounting hole.

These "hash chokes" are single layer closewound with 14 or 16 AWG (depending
on your xmfr size and primary current) enameled magnet wire.  Two filters
are made --- one for hot and one for the neutral side of the power line.

This does a nice job of seizing low frequency transients before they hit the
normal RFC line filter.

Coming from the xmfr primary end towards the power inlet, the progression is
(1) hash filter, (2) MOVs, and (3) RFC line filter.  This triple filter
method supresses most anything that will interfere with your neighbor's
electronics and keeps you out of the "mad scientist" regime.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
 >
 > http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg
 >
 > works like this.
 >
 > MOVs - The MOVs provide absolute "fool proof" protection against over
 > voltage right at the NST.  They are 1800V +-10%.  Unlike a safety gap,
 > there is nothing that can go wrong.  As I was working on this filter,
 > reports of miss-adjusted safety gaps were very common.  So I added the
MOVs
 > since there was no adjustment.  Today, folks seem better at adjusting gaps
 > so it is not as much of a problem, but the MOVs simply can't allow the NST
 > to go far past spec no matter what happens.  Ideally, if the system and
 > real safety gap are adjusted right, the MOVs will never do anything.  I
 > have had reports of MOVs burning up, but practically no reports of failed
 > NSTs :-)))  If run too hard, the MOVs melt internally and hard short out
so
 > even under the worst conditions they will still save the NST.  Also, if
the
 > MOVs "get warm", that is an early indication of system problems.
 >
 > RC Filter - The filter is set at about 290kHz.  It is really not designed
 > to filter the Fo frequency but rather the 30MHz type harmonics and giant
 > initial firing noise.  If the frequency were much lower, the loss in the R
 > or the large C would start messing with the coil's operation.  The way
NSTs
 > are wound, the inductance, resistance, and capacitance of the HV windings
 > is "sort of" uniform across the winding.  "Few hundred" kHz stuff does not
 > do much harm.  But >1MHz bursts can hit the outer layers of the winding
 > pretty hard and cause local breakdown.  So the RC filter really is to
 > stop >1MHz type signals rather than the fundamental.  The filter also
 > provides drain resistors to the entire system (they are hiding in there
 > ;-)) but now with MMCs that is not a big deal.  There is inductance in the
 > resistors I use but ringing affects are swamped by the resistance and the
 > small inductance really has no affect other than perhaps lowering the
 > cutoff frequency a little.