Re: Please Advise

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Emmett,

The 6 x 30 toroid pulls the sec Fres near 218 kHz. The inductance required 
in the primary using the 0.0375uF cap size is 14.2uH. L = 1/(4*pi^2*F^2*C). 
That works out to 5.53 turns (9.5" ID, 15.026" OD -at-5.53 turns). Coupling at 
this sec to pri proximity is 0.11.

Remember when I said,
"It will be interesting to see if you actually gain any sparklength between 
your current toroid size and whatever you decide on next, or if the spark 
formation changes only."

The reason I stated this is because I don't show a spark length increase 
with the larger toroid with my calc's which is based on energy and time at 
the gap. However, I do show about 100kV higher potential at the top 
terminal by Vtop=eVpxsqrt(Cpri/Cee) [peak volts]. Meaning, if the toroid is 
smooth, it should breakout at a higher potential than with the smaller 
toroid. The added toroid size with center disc is adding secondary 
shielding to the top of the secondary. This changed the current 
distribution along the secondary length. Now, you should be able to 
increase coupling higher than you could have done with the smaller toroid 
(by how much I'm not sure). Even the smaller toroid could have had a 
coupling adjustment as I had mentioned in the past.

Typically, coupling above mode 5,6 will cause racing sparks (ref. Antonio's 
discussions on Total Energy Transfer in the archives). 
k=(b^2-a^2)/(b^2+a^2), where b=a+1. Mode 5,6 refers to a=5, b=6, and works 
out to k=.018 and will take 5.56 half-cycles to complete or 12.51us. I'll 
run Javatc for a "desired k of 0.18". This will change the primary height 
in relation to the secondary height.

WOW! This is what occurred; The primary had to be raised 4.915 inches above 
the base of the secondary! Yipes! Typically, a coiler would lower the 
secondary into the primary 4.915 inches to accomplish this adjustment (same 
effect). But, I think you can see why I say "Yipes!. That puts the primary 
only 17.585 inches away from the topload. Arcing to primary may be a 
problem, but that is difficult to say.

Now, "mode 5,6" is an "ideal" case. As we know, nothing is "ideal". It 
still takes some manual effort to find the best position, but these modes 
do provide good starting points.

You may want to go for mode 6,7 or k=0.153 (this is typically where I 
start). For your coil, the secondary should be lowered 2.5 inches below the 
inner primary turn to achieve this coupling coefficient. If you see racing 
sparks, it means k is too high and you need to come up slightly (say 1/4" 
increments) and try again.

With this coil, your tune point will not be affected (I checked this during 
the evaluation). Also, if you decide to setup for k=0.153 and you get 
intermittent racing sparks, before lowering, try detuning to about 8% 
(right at turn 6), then try again. You may even want to leave it there and 
then reduce k in small incremental steps.

I hope this helps.
Take care,
Bart


Tesla list wrote:

>Original poster: "Emmett Secrest" <secrest2032-at-msn-dot-com>
>I built the 6x30 Toroid and when I tried it out I got less numbers of 
>streamers and shorter length.  I put the 4x21 Toroid back on retuned and 
>again produced more and longer streamers.  Both toroids tune in the 4.5 to 
>5.5 turn range. I was rather tired by the time I had finished building the 
>6x30 so I didn't get to test things out totally, I will be testing 
>further. I don't understand why the larger Toroid performed poorly or why 
>the tuning is so similar between the two.