Re: 2 layer primary puzzle

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

James,

The problem is that magnetic field created by the the top winding is being
canceled out by that of the bottom winding. The fix is simple - flip one
winding 180 degrees so that the magnetic fields of the two primary windings
are additive. Now let's answer your specific questions (below): 

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.

This is true only for the independent primary and the secondary windings.
it is NOT true if the same current is forced into both windings as it is in
the 2-layer primary. 

> 2. understanding/myth - the "mutual inductance" of the 2 coils increases
> inductance, not cancels out the
> others inductance.

It depends upon the "sense" of the two windings. If the windings are
connected in series as they are in your 2-layer primary, the mutual
inductance can be either positive if the windings aid each other's magnetic
fields, or negative if they oppose each other's fields. Your windings are
either both wound CW or CCW. The fix is to insure that they are CCW and CW. 

> 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!

Answer already provided above. 

> Any comments will help. Thanks,
>  James Cart

Good luck, and best regards!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com