Re: Secondary length question

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

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

In a message dated 6/21/01 8:33:38 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes:

> Hello, after I just finished my first coil (1"X8" Sec.) I have an urge to go
>  bigger. I have some 4 inch PVC pipe sitting around and I am wondering, what
>  would be the optimum length to wind a secondary on that? I have heard of
>  everything from 4"x12" to 4"x36". What length should I go with? I think 
that
>  4"x24" would be best but any comments and suggestions are appreciated.
>      Thanks, Jake.

Jake,

If you plan to get rather long sparks such as 70" and if you plan
to run at 120 bps, then you'll need to make the secondary longer
than 4" by 24", or you'll get racing sparks due to the large bang
size.  If you run at a higher bps, the 24" secondary will work
because then the bang size can be smaller.  In the high bps
case, you'll be growing the sparks via breakrate.

If you just want up to 60" sparks, then you can use the 24" long
secondary even at 120 bps.  If you use a static gap, the bps
will depend on the relative cap value vs the xfrmer (assuming
NST power), and the gap spacing.

If you want longer than 70" sparks, then you'll need to use
higher bps, and also make the secondary taller than 24".
Perhaps 27" or 28" would be good.

To summarize, the needed secondary length depends on the
power input and breakrate.  Higher power inputs require a taller
secondary, and lower breakrates require a taller secondary, in
general.  You can always make the secondary a little taller
than needed for more resistance to racing sparks and breakdown.
Going too tall makes the coil bulkier than needed of course.
A downside of a short coil is the streamers tend to strike down
to the primary.

John