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Re: [TCML] Are safety gaps necessary?
Yes indeed! I'm thinking only about the static gap scenarios. For pigs, however, this probably means air-blast or "sucker" types. Thinking more about those gap types makes me wonder if the tendency there will be to effectively set the gap too wide by accident--maybe even most of the time!--since cranking up the air flow and hence the pressure in the gap is equivalent to widening a non-pressurized gap. That may be a source of some unexpected performance with those gaps. In such situations, it is also probably helpful to have a protection device with a more constant breakover voltage, both to guard against things like primary strikes and also human error.
So I suppose I've convinced myself that safety gaps are worthwhile in all but the wimpiest, most unusual endpoint-gounded NST scenarios sans actively quenched gap.
--- On Thu, 6/19/08, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
> From: bartb <bartb@xxxxxxxxxxxxxxxx>
> Subject: Re: [TCML] Are safety gaps necessary?
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Thursday, June 19, 2008, 6:34 PM
> Hi Aaron,
> Yes, Gary does bring up a point I had not considered (and
> I'm still
> rummaging through my head on it). On my pig, I run similar
> to David
> Reiben with one of my ears at RF ground. However, with PIG
> coils were
> usually talking rotary gaps and **ALL** rotary gaps should
> use a safety
> gap! This is very different than a static gap that has a
> clamping voltage action. Rotary gaps can and will miss a
> firing here and
> there and since timing is in control, there is no clamping
> occurring. Thus, a safety gap serves this specific purpose.
> jaholmes@xxxxxxxxxxxxxxxxxx wrote:
> > Gary's point about three-terminal safety gaps
> makes perfect sense to me when I think about
> midpoint-grounded NSTs. I'm willing to believe that a
> three-terminal gap is important in that case. In
> endpoint-grounded scenarios, such as with lower-voltage
> NSTs or one-eared pole pigs, it seems like the necessity of
> a safety gap would depend somewhat on the likelihood of a
> strike on the *transformer* side of the main gap. In a
> table-top coil with endpoint-grounded NST integrated into
> the base, the chances of a strike to the transformer-side
> primary wiring seems unlikely. And if such a strike *did*
> happen, the main gap is very close to the transformer. On
> a larger PT- or pig-powered coil with ten feet of wiring
> between transformer and coil base (where the main gap might
> be), strikes to that wiring seem much more likely and
> potentially damaging. What effect will all that wire and
> its inductance have on the main gap's ability to act as
> a safety gap and
> > prevent the strike from damaging the transformer?
> That seems like something worth worrying about.
> > In the end, of course, this is all of little practical
> importance if even a single scenario can be found where a
> safety gap is useful. After all, safety gaps are cheap and
> easy to build, and "best practices" are easier to
> write down and remember.
> > Cheers,
> > Aaron, N7OE
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