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Re: [TCML] gaps
Hi Mike,
As with life, many Tesla Coiling questions have no simple black or white
answers... :^)
A well-designed static spark gap can provide excellent performance. The
most efficient static gap appears to be a single gap with high velocity
air flow (a "sucker gap" or air blast type). Because of individual
voltage drops within the gaps, multiple static gaps can have higher
overall voltage drops (thus being lossier), but they can have superior
quenching capability at less than heroic air velocity. Under similar
quenching conditions, the single gap may slightly outperform a multiple
gap that has a similar breakdown voltage. Static gaps are also
recommended for first-time coilers for reasons discussed below.
Static gaps can't wring out maximum performance in NST systems. Static
gaps tend to fire chaotically when used with an inductively
current-limited transformer (such as an NST or ballast-limited pig).
This causes multiple bangs during each AC mains half cycle that are of
varying (and suboptimal) size. In order to get maximum spark length
versus input power, best results are obtained using a synchronous rotary
spark gap (SRSG), or a synchronously triggered static gap, combined with
a larger size tank capacitance (see below). A properly adjusted SRSG
consistently forces the gap to fire so that each bang is of the same,
optimal, size - once on every incoming half cycle of the power mains.
In earlier days of coiling, many folks destroyed their NST's when they
converted from static to rotary gaps. These were also the days when the
accepted practice was to design coils where the tank capacitor was
"tuned" to resonate (at mains frequency) with the NST's leakage
inductance, a practice known as "mains resonant charging". Indeed, many
TC design tools defined this as the optimal tank capacitor size for a
given NST voltage and current. For a 15 kV NST, this was about 0.01 uF
for every 30 mA of output current for a 60 Hz supply. Unfortunately, if
the main gap was set too wide, the rotary gap was improperly adjusted,
or the RSG was merely running too slowly, the voltage cross the NST
could rapidly grow to ridiculously high voltages. This usually resulted
in overvoltage failures of NST's, or for pig-driven systems, tank
capacitors.
Over the years, it was learned that, by using a larger sized capacitor
(called Larger Than Resonant or LTR), mains-resonant overvolting could
be avoided. Adding a properly adjusted safety gap placed directly across
the NST output terminals protects the NST from overvolting under
other/abnormal circumstances. Terry Fritz's "Terry Filter" adds an
additional layer of protection, especially against high speed transients
that can cause inter-turn corona damage within the outermost turns of
the NST windings. It even protects against an improper safety gap setting.
The bottom line line:
A system using a synchronous rotary gap, an LTR tank cap, a properly set
safety gap, and a Terry Filter is every bit as reliable as a system
using a static gap. The SRSG system also provides higher performance
than a similar static gap system.
Bert
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Mike Doyle wrote:
a rotary spark gap,isnt as effective,as a stationary 4 gap,setup? i use neon sign transformers,and its safer,to use them,with a stationary gap0. true,or false?
mdoyleufo@xxxxxxxxx thanks mike.
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