Re: secondaries

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>





<Hi all, 

<Just wondering. My new coil will be 10 or 12" diameter. 5 years ago, 
<Richard Quick and Hull used to say that coils of this size should be 
<wound with an aspect ratio of 3:1 eg: 10" diameter = 30" long. They 
<should then be wound with a wire that allows between 800 and 1000 turns. 
<I've taken this advice with all my coils and have had some good 
<results. However, lately, I have noticed some web sites with 10 and 12" 
<coils (eg: Robin Copini's page and HVGUY) that have very large aspect 
<ratios (4:1 and over). Has this general 3:1 rule changed since I last 
<made a coil? What is the "general rule" these days? 

<Cheers, 

<Greg Peters 

<IMO a 10" secondary 
<should be about 60" tall or so, maybe even taller.  The narrow 
<secondary has less self capacitance, and permits a larger toroid 
<to be used for a given input power.  A tall narrow coil tends to be 
<light weight, and can tolerate cheap, lightweight, thin wire.  The 
<sparks from a tall secondary are less likely to strike down and 
<hit the ground or the primary. 

<My small coil, etc. is at: 

<<<<http://hometown.aol-dot-com/futuret/page3.html 

<John 

Greg, John, all, 

I tend to agree with Greg on the aspect ratios, at least of 
larger coil systems. While a narrower secondary would 
naturally have less distributed self capacitance, which is 
a plus, the shorter, fatter secondaries have higher induc- 
tance density, which is also a good thing, especially for 
big coils. When you are running multiple kVAs of input, 
heavier wire and higher inductance becomes more impor- 
tant. My 10 kVA pole pig driven system uses a 12" dia. 
secondary coil that is only 38.5" long but with proper tun- 
ing and a good toroid, I can easily get 10 ft sparks from 
it. And I know the efficiency could be considerably better 
(about 6 to 7 kVA in yields about 9 ft sparks). BTW, the 
secondary coil wire is apprx. 660 turns of # 16 AWG dbl. 
Formvar coated magnet wire. 

With the smaller NST type systems, then the higher as- 
pect ratios are the order of the day, and I can't think of 
anyone who has futher optimized the efficiency of the 
smaller NST systems for max output more so than John 
Freau :-) I just tend to think that the lower aspect ratios 
are better for the larger, high-powered systems. Just MHO. 

Sparkin' in Memphis, TN, 
David Rieben