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RE: Naming a coil size, was Re: Big Coil

Original poster: "Ken Jenkins" <thecompman@xxxxxxxxxxxx>

Thanks for that info, I was surprised at the output of
this coil!
On the first run at my friends shop we fried his 4 line phone
system. :-( $$$.
ken J.

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, January 26, 2005 10:51 AM
To: tesla@xxxxxxxxxx
Subject: Naming a coil size, was Re: Big Coil

Original poster: FutureT@xxxxxxx

In a message dated 1/25/05 11:01:57 AM Eastern Standard Time,
tesla@xxxxxxxxxx writes:

>Original poster: "david baehr" <dfb25@xxxxxxxxxxx> > > >80" sparks from a 4.5" coil !!! WOW, could you give me a few specs on your >coil ? I'm gettin' just over 48" with my 4" coil,....,,,,Hmm, thinking >back, my very first coil was about 4" dia. , pvc wire on an ol' carpet roll >tube with glass plate caps and single spark gap , discharge was about 4" , >Look how far we have come!!

I think that the somewhat common practice of naming coils by their secondary diameter does not give a true indication of their spark length capabilities. Consider for example a 4" coil that is 15" tall, and another 4" coil that is 25" tall. The taller coil will be capable of giving much longer sparks before the secondary is destroyed by racing sparks as the power input is increased. In fact the taller coil will be able to give sparks that are about 1.67 times longer. That's because the taller coil is longer by that factor in the above example. For example if the shorter coil can give a 50" spark, then the longer one would give an 83.5" spark. Of course the taller coil will require (and will be able to withstand) a higher input power to get the 83.5" sparks. I'd suggest that naming a coil by its height would give a better measure of its capabilities. It's true that a wider diameter sometimes helps efficiency, but the ability to withstand a large input power depends more on the height than the diameter at least up to some point. Of course it's desireable to keep the ratio of dia to height within an acceptable range.

In one of my experiments I compared the performance of a
4" x 23" secondary, and a 6" x 24" secondary.  There was no
real difference in performance, and no real difference in power
handling capability, because they were both of similar height,
(or length if you prefer).