Re: Please Advise

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

Original poster: "Emmett Secrest" <secrest2032-at-msn-dot-com> 

Bart...just to give you an update on the Toroid change.  As I said 
previously I produced less numbers of streamers with the 6x30 Toroid and 
they also did not appear as bright and were not as long as with the 4x21 
Toroid.  Again tonight I had the same results. I decided to change my 
overall spark gap setting since either you or Dan had stated I was pushing 
it with a total of 3/8".  I changed the total gap to .165" and was 
surprised by the results.  It required re-tuning .5 turns out from the 
center. It went from 4.5 turns to 5 and 1/6th turns for the 4x21 Toroid and 
6 and 1/6th turns for the 6x30 Toroid. Can you explain why changing the 
total spark gap setting affects the tuning point?  This is probably basic 
stuff for you experienced coilers but it really has my curiosity peaked.  I 
think the 6x 30 may be a little large so I am going to cut it down to 24" 
O.D. and give it another try.  I will also try your suggestion on raising 
the primary via lowering the secondary. I originally had it set at 2.5 
inches up from the bottom winding of the secondary. Honestly I had 
forgotten about that and it is an easy change. The results should be 
interesting. I did receive some racing sparks on the secondary with the 
6x30 Toroid.  I'm not sure what I did to stop them but it hasn't happened 
again with the large toroid. With the 4x21 and the new gap setting I am 
getting two to three streamers at a time that are very bright, seem to be 
wider than before and are around 4 feet in length. I am not positive on the 
distance as I have not tried to accurately measure them.  Lets just say 
they are nice streamers and they make me very happy.  Oh , one other 
question, is the .165" gap acceptable or do I need to decrease it further?

Thanks,

Emmett

----- Original Message -----
From: <mailto:tesla-at-pupman-dot-com>Tesla list
To: <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
Sent: Sunday, January 04, 2004 8:08 PM
Subject: Re: Please Advise

Original poster: Bart Anderson 
<<mailto:classi6-at-classictesla-dot-com>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" 
<<mailto:secrest2032-at-msn-dot-com>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.