Re: [TCML] Safety gap firing - (JAVATC Questions)

["DC Cox" <resonance@xxxxxxxxxxxx>]

This sounds like you don't have enough primary turns to bring it into proper
resonance.  that's why building a "scrap wire" pri on slitted cardboard with
perhaps 16-20 turns is very important and will allow you to select a full
tuning range to find best resonance.

Personally, I never use safety gaps --- no reason to.  The low cap value
caps will conduct any high freq currents to ground and the varisters will
clip any overpotentials directly to ground.  I use a modified form of the
Terry filter and definitely include two small inductors which clip any input
high freq spikes before going thru the Terry filter.  Also, I break the
resistances up putting one before the caps to ground and one after the caps
to ground.  I then just use 25 Watt resistors (two in series on each leg).
With the high speed varisters there really is no need for any type of safety
gap.

If you contact me off-list I can email you the schematic.  It works good as
our commercial small coils in museums runs 6 days per week, 2-3 shows per
day, year after year without failure.

Another mistake many experimenters make is using my plans and then they
start modifying things.  The plans I send out work 100% all the time --- as
long as you don't go off and start modifying things.  Then, you go out on a
limb where ferro-resonances and other interesting things such as
constructive-destructive interference occurs, reflected waves, etc, etc.
Many people will modify the sparkgap from what I recommend, and this can
cause major performance changes in a small coil.  Improper quenching and
improper coeff. of coupling are two areas we test and research extensively
using expensive equipment to "see" what is happening.  We adjust our designs
so problems do not occur.  Modifying our design is asking for trouble unless
you have a lot of test equipment to verify the outcome of any change.

Dr. Resonance





On Sun, Apr 20, 2008 at 4:59 PM, <otmaskin5@xxxxxxx> wrote:

> This has been the most frustrating part of my coiling experience.? When
> running the coil, my safety gap fires anywhere between frequently and
> constantly.? I have tuned, re-tuned, re-re-tuned ad-infinitum, raised &
> lowered the toroid, raised & lowered the secondary, rebuilt components
> including the safety gap, the MMC, spark gap & tried several suggestions
> from this group.? In well over 2 years of coiling, I have not been able to
> solve this problem
>
> I have my static spark gap closed down so far, that I'm surprised I even
> get any sparks at all (although somehow, I am getting?pretty decent
> sparks).? But I know I'm seriously limiting performance.? Right now, I'm
> down to a 0.12" spark gap with a 15/60 NST - & STILL get some safety gap
> firing.? The NST connected only to the spark gap easily fires all nine
> segments for 0.27" total gap every time I try it.? I know a lot of guys are
> running much wider than I am.? Seems like from everything I read from other
> coilers, they are at 0.25" spark gaps or more.? The Dr. sent me plans for a
> 12000 NST coil with a 0.25" gap spec.? I'm not looking to go crazy
> overextending my components with an improperly wide spark gap, but my
> current 0.12" seems ridiculously low.
>
> I am going to try resetting the safety gap as Bart suggests, although what
> he describes seem pretty close to what I did.? I'm also going to find
> someone with a scope & signal generator locally to verify tuning.? But
> beyond that I'm stumped.? I'll let you know?what happens.? Thanks for
> listening.? Dennis Hopkinton MA
>
>
> -----Original Message-----
> From: bartb <bartb@xxxxxxxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Sun, 20 Apr 2008 6:17 pm
> Subject: Re: [TCML] JAVATC Questions
>
>
> Hi Dennis,?
> ?
> Yes, 1/8" total gap. This is a safety gap and your main gap is something
> else, right? The "safety" gap you will have to experiment with even after
> it's on the system. The main gap should be set to just fire with the
> transformer. The safety gap should be set to not fire except if the main gap
> has a problem. How often the safety gap fires will depend on the regularity
> of the main gap. If the safety gap fires too often, it can heat up and then
> start firing more and more often as the electrodes heat and as the air
> around the safety gap becomes more ionized.?
> ?
> Take care,?
> Bart?
> ?
>
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