Re: Coil behavior

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Original poster: "resonance" <resonance@xxxxxxxxxxxx>




Whenever you set up a new coil design always first make up a "scrap 
wire" primary.  I use some old 12 AWG house wiring (single conductor) 
and hold it in place by cutting small slots into pieces of 
cardboard.  For nst powered coils, I usually use 20 turns for every 
initial test.

Scrape a bare spot every turn and stagger them offset 1 inch so they 
are not all in alignment --- prevents pri flashover while testing.

Until you hit resonance always keep the variac power setting at less 
than 50%.  Also, good idea to keep sparkgap max settting to approx 
.060 (60 mils) until tuning is finished.  After finding resonance 
point, then open up sparkgap to a max of 0.200 (200 mils) and you can 
bring variac up to 100%.

This allows a quick test for tuning parameters without setting up a 
beautiful copper tubing primary only to discover you don't have 
enough turns to resonate the pri with the sec.

Another tip is try to set the total primary turns to approx 8-12 
turns with nsts.  You accomplish this by gradually adding more 
capacitance (hence more energy into your pri) and slowly reducing the 
number of turns until you hit 8-10.  Then you have max capacitance 
for your system (best energy input) and a suitable number of turns on the pri.

Very Important ---- Don't feel bad!  We've all made these 
errors.  It's really part of the process as you become an 
accomplished coil builder ---
usually first failures followed later by many successes.

Also, be sure to try Bart Anderson's JAVATC program.  It will give 
you precise answers with your pri cap and number of turns 
values.  I've used it a lot for both classic and solid state coil 
designs and it works great! Terry's TeslaScan is another invaluable 
coil design program that also works excellent.

One of the greatest advantages of using these programs is that it 
allows you to experiment numberically with different values of pri - 
sec spacings and advises you of the coeff. of coupling value (k) for 
each setup.  Set your k value between 0.18 and 0.20.  Never exceed 
0.22 as this will usually produce racing sparks.  The 0.18 to 0.20 
range of k will give you the optimum pri - sec spacing such that your 
setup will produce the maximum secondary spark length with a fixed 
input power level and fixed pri capacitance value.

Even coil builders with present setups may wish to run their pri - 
sec spacings thru JAVATC and check their coeff. of coupling --- an 
adjustment (new pri configuration) usually leads to increased 
performance from almost any existing system unless you were lucky 
enough to hit it perfectly on the first try).

These are both available free from the program's designers --- take 
advantage of it!  I use JAVATC in every new design I do.  It takes 
all the guess work out of the process and helps we optimize the 
design on the first attempt.

Many happy long sparks,

Dr. Resonance


> I'm afraid to ask but I think I may be lacking in primary turns. I'm 
> running a resonate coil (poor planning on my part). That said I'm 
> running very conservitave spark gap settings. One of the issues I'm 
> running into is I have my tap connected to the very end of my 
> primary (15 turns counting the tap lead). I dont' get streamers at 
> any other position but the one I just mentioned. If I connect to 
> turn number 14 I get nothing. I do notice however that my safety gap 
> (Terry's Filter) fires solidly at turn 14 and any other turn for 
> that matter and no streamers. The safety gap fires quit frequently 
> even at primary turn 15 but more pronounced at 14. ( I just realized 
> I  should prolly open up the safety gap a hair while proof reading my post.).
>
> My question is can I adjust anything besides adding extra turns to 
> the primary? Can I use a smaller toroid, raise/lower the secondary 
> or raise/lower the topload? I really don't want to re-build the 
> primary. JavaTC says I should be tuning at 13'ish turns. I tried 13 
> and get nothing but a safety gap arc. I know I'm doing something wrong.
>
>
> Transformer: 15/60
> Primary: 15 turns of 1/4 copper tubing.  (including Tap lead.)
> Secondary : 4" and 23" of actual coil on a 25" form. (first turn 
> level with primary, maybe a hair above)
> Toroid: 4x19 sitting at 25" high.
> MMC:  .0093uF  (Ya I know I'll build another one)