Re: Arc Over Between Secondary and Primary Coils

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Nolan - 

Thanks for sharing "all" the specs (enough anyway to play with). There is one
thing missing however. The type of primary (helix? spiral? angled?).
Regardless, I played with the numbers anyway (I just love doing that). 

First, input parameters to JavaTC. Next, ran ETesla6 to get the toroid affect
on coil frequency. This was amazing! I ran the wall and ceiling distances far
enough away so their affect would be negligible. I simply ran the secondary in
ETesla6 and Fres = 488.8kHz (wow!). By wow, I mean the toroids effective
capacitance dropped from 10.4pF to only 5.9pF. This was performed by simply
changing the % Reduction in JavaTC until JavaTC Fres matched ETesla6 (this is a
43.8% drop in top capacitance from an alone in the universe capacitance
equation due largely to toroid to coil side). 

Now, for a spiral primary, it should tune in at 4.05 turns. A helix would tune
in at 5.48 (not changing inner diameter). The BIG difference is coupling. With
a spiral, JavaTC showed 0.1055 with height at 0. The helix showed 0.2408 a same
height (a little high, see Acmi below for better results). 

I'm not sure which you have, but if it's helix, the coupling may be rather
high. If coupling is too high, racing sparks can occur. Some of these shoot
down and out to the primary. I remember having coupling too high on my large
coil and arcs shot down from the top and out near the middle of the coil to the
primary. Raising the secondary or lowering the primary will reduce the
proximity of one to the other which reduces mutual inductance and coupling. 

Ran Acmi from 3" above and below for both types: 
Flat spiral: 
 PRMY.h|    PRMY.L| PRMY.R|    SCNY.L| SCNY.R|PRMY-SCNY.M|PRMY-SCNY.K 
 -3.000|   3.45 uH|   0.00|9379.04 uH|  42.36|    4.89 uH|     0.0271 
 -2.000|   3.45 uH|   0.00|9379.04 uH|  42.36|    7.59 uH|     0.0422 
 -1.000|   3.45 uH|   0.00|9379.04 uH|  42.36|   12.19 uH|     0.0677 
  0.000|   3.45 uH|   0.00|9379.04 uH|  42.36|   19.05 uH|     0.1058 
  1.000|   3.45 uH|   0.00|9379.04 uH|  42.36|   25.90 uH|     0.1439 
  2.000|   3.45 uH|   0.00|9379.04 uH|  42.36|   30.47 uH|     0.1692 
  3.000|   3.45 uH|   0.00|9379.04 uH|  42.36|   33.13 uH|     0.1840 

Helix: 
 PRMY.h|  PRMY.L| PRMY.R|    SCNY.L| SCNY.R|PRMY-SCNY.M|PRMY-SCNY.K 
 -3.000| 2.01 uH|   0.00|9379.04 uH|  42.36|    5.68 uH|     0.0413 
 -2.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   11.32 uH|     0.0844 
 -1.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   19.61 uH|     0.1461 
  0.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   27.71 uH|     0.2065 
  1.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   32.65 uH|     0.2433 
  2.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   35.05 uH|     0.2613 
  3.000| 1.92 uH|   0.00|9379.04 uH|  42.36|   36.25 uH|     0.2702 
Note: not sure why -3 in helix showed PRMY.L at 2.01 uH. 

Take care, 
Bart 
  

Tesla list wrote: 
>
> Original poster: "tmoore by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <tmoore-at-erie-dot-net> 
>
> Hello Everyone, 
>
>     This is Nolan I have been working on a new mini tesla coil that I just 
> finished building.  My mini coil specs are 
>
> Secondary:  2.375 in diameter by 15in high wound with Awg 28 12.75 in long 
> 10 or more coats of polyurethane 
> Primary: 6awg ground wire 0.25in spaced between turns max turn 8.75 1in 
> spaced from secondary 
> Topload: Toroid length is 9.5in and 3.375 cord, made from flexible Al tubing 
> wrapped 3 times in Al tape 
> Cap: Maxwell pulse discharge 0.03uf rated at 35kv 
> Spark gap:  single static gap .25in carriage bolts set at 0.15in just below 
> transformers max spark length 
> Power Supply: Franceformer 7500kv at 60ma 
>
>     My problem it that I am getting massive arc over from the middle of the 
> secondary coil to the primary.  I noticed that when I had sparks coming off 
> the topload to a grounded object 8in or close that there was no mid 
> secondary to primary coil ark over at all.  When I move the grounded object 
> away and let sparks go in to the free air I get tons of arc over.  Is this 
> because the grounded object doesn't let enough energy to be stored and thus 
> there is no arc over? Anyway I need a solution!  I was thinking about 
> removing a turn or two from the primary, one turn would make the distance 
> about 1.4in and tow turns removed would be about 1.8in, but I would be 
> getting low on turns.  Would .4in or .8in more solve my ark over problem? 
> If not any tips or suggestions that would help are greatly appreciated. Also 
> I found that when I adjust the spark gap smaller and sand the electrodes 
> every time, this greatly reduces arc over but also diminishes the spark 
> length off the topload. Any ideas on spark gap? Thanks for your help! 
>
> Sincerely, 
> Nolan Moore