RE: How much does aspect ratio of secondary really matter (is it all about K factor)?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Hello All,

K factor or coupling factor directly affects the mutual inductance which
wants to be as high as possible (without racing sparks)- therein lies the
catch in coil geometry, yes? This isn't spoken to very often and a
description of it would be a good thing for us aspiring coilers.

Jim Mora


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, May 31, 2006 3:15 PM
To: tesla@xxxxxxxxxx
Subject: Re: How much does aspect ratio of secondary really matter (is it
all about K factor)?

Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>



The low 2:1 ratio might present some tempting sparks from top of sec
to bottom of sec.  Testing will tell the story.  At low power you
might get away with it.

Dr. Resonance



>I've been crunching numbers on a low-power,
>low-frequency coil, and one of the options that has
>presented itself (while playing with JavaTC) is going
>with an aspect ratio less than 3:1 (specifically:
>2.5:1).  For whatever reason, conventional wisdom
>calls this "not recommended", however going with a
>short-and-fat secondary permits me to match the low
>frequency of the primary (which is due to low voltage
>and large primary cap) while maintaining a low
>profile.  Since the coil is only going to be ~150W or
>so and can't be expected to put out sparks more than
>24" or so, I don't want the physical size of the coil
>to promise more than it can possibly deliver ;-)  For
>that reason, I'd rather grow "out" than "up".
>
>All talk of aspect ratio that I can find seems to
>center on K factor, however the K factor I get out of
>JavaTC for this 2.5:1 ratio coil is 0.17, which seems
>"normal" to me.  Any other gotchas associated with low
>aspect ratios?  If I have coupling under control,
>should I be "ok"?
>
>Best regards,
>Aaron, N7OE
>
>