Re: secondaries

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Greg,

On 8 Oct 2001, at 11:51, Tesla list wrote:

> Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
> 
> 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?

Some theoretical work and measurement shows that the lower aspect 
ratio scores a higher unloaded Q for the same length of wire. 
However, the unloaded Q's are so high anyway (typically 200 upwards) 
that going to a higher aspect ratio has more benefits: a much higher 
voltage handling capability and moving the business end of the coil 
further from the primary to minimize strikes in the vicinity of the 
primary. From a personal angle, while strikes near the primary don't 
worry me, especially if there is a guard ring fitted, I think it 
rather detracts from the display to have arcs constantly shooting 
vertically rather than splaying out in all directions.

Regards,
Malcolm