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Re: 2 layer primary puzzle



Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "James T by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jamest2000-at-att-dot-net>
>
> Hi Everyone,
>  I will keep this brief. I am working on an 8" coil with a 2 layer primary.
> I have constructed the primary and
> it is not behaving as I expected. I measured the inductance of the primary
> by itself.
>   What happens is, I measure from the outside of the top coil to the inside
> and the inductance goes up as
> expected. Then I drop down to the bottom layer and measure from the
> top/outside to the bottom/turn, oops, the
> inductance goes down as I go out. The inductance of the bottom coil seems
> to cancel the inductance of the top
> coil. Please set me straight on this.
> 1.understanding/myth - the winding direction between the 2 coils is
irrelevant.
> 2. understanding/myth - the "mutual inductance" of the 2 coils increases
> inductance, not cancels out the
> others inductance.
> 3. 2 layer primary's are a practical approach. I seem to recall some posts
> on this, and it was considered
> reasonable. Brilliant to ask now that it is done!
> Any comments will help. Thanks,
>  James Cart

Hi James...

mutual inductance matters if the coils are wound in the same direction...
if wound in opposite
directions and in very near proximity to each other they have a tendancy to
average out (
sometimes cancelling each other if the coil is small enuf)

I tried the dual primary and found it to be a real bear to tune ( wasted
quite a bit of tubing
too) also had problems with alot of inter-primary arcing between the two
coils...

what I did find out tho was if you wind the "top" coil from inside to the
outside and then
drop down to the lower coil and continue to wind in the same direction from
outside to inside
on the lower coil, the inductance seems to be nominal..

when i retried the winding part again to increase things  I wound the "top"
coil from inside
to outside and then dropped down to the lower coil and wound outside to
inside BUT in the
other direction

the results were increased performance... but not by too much..


Scot D