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Re: How much does aspect ratio of secondary really matter (is it all about K...

Original poster: Mddeming@xxxxxxx
Hi Aaron,

The chief problems with low ratio coils is the inter-turn potential difference, the potential gradient along the secondary and the physical proximity of the toroid to the primary. These translate into insulation puncture, creeping sparks, and primary strikes, and a greater tendency to flash down the inside of the secondary. Other than those four possible disasters, there is no major problem. ;^)))

Matt D.

In a message dated 5/31/06 6:30:48 P.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes:

>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