Re: Off-axis tuning coil? (was: I Think I Messed up!)

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Jim,

On 6 Dec 2001, at 16:48, Tesla list wrote:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> The resonant frequency is determined by the total inductance and
> capacitance. An off axis inductor adds inductance (lowering the Fres) but
> doesn't change the coupling between primary and secondary.

Actually, it should since you now have additional inductance in the 
primary which is not coupled to the secondary. I would expect this 
arrangement to obey the coupling rules as formulated by Dr de Queiroz.

Regards,
malcolm

 Also, some of
> the primary voltage will be developed across the second inductor, but, this
> isn't all that important.  Current is what makes magnetic field, and
> they're in series, so the current is the same in both inductors.
> 
> If you have the axis of the added coil the same direction as the axis of
> the primary coil, then the field from the added coil will either add or
> subtract from the field from the primary (depending on the direction of the
> turns and how you've wired it.
> 
> The added inductor can be either a flat spiral or a standard helical (i.e.
> a coil looking thing)
> 
> For size and formulae.. You presumably know what the resonant frequency of
> your secondary is.  You also know what the inductance of your existing
> primary, and the value of the capacitance is.
> 
> The basic thing you need to know is how much added inductance you need:
> 
> 
> Ls*Cs = Lp*Cp
> Ls*Cs = (Lp + La) * Cp
> 
> rearranging:  La = (Ls * Cs)/Cp = Lp
> 
> 
> For formulae, you can use the standard things...
> 
> L = r^2 * N^2 / (9*r + 10 *L) , r = radius (inches), L=length (inches), L
in uH
> 
> for what it's worth, a 3" diameter, 8 inch long coil with 15 turns is 0.36 uH
> 
> A pancake 6" to the center, with a 4" hole in the middle, and turns spaced
> 1/2"apart is around 30 uH...
> 
> 
> Tesla list wrote:
> > 
> > Original poster: "Patrick Leonard by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <transactoid-at-rogers-dot-com>
> > 
> > Someone suggested I use an additional coil in series with my primary to
> > increase the inductance. I've only ever seen one or two other coil like
this.
> > It had maybe only 4 or 5 turns, and used an additional coil of maybe 7 or 8
> > turns from which a wire was used to tap the secondary. I think the builder
> > called it an off-axis "tuning coil".  One of the coil's on
> > <http://www.hvguy-dot-com>www.hvguy-dot-com also has such a "tuning coil".
> > 
> > How would I calculate the dimensions, or is this something I can just
kind of
> > guess at? Also, is it wound flat spiral like the primary or cylindrically?
> > (that's how the above tuning coil was made).
> > 
> > Lastly, how does such an addition work? >From what I understand, the flat
> turns
> > of the primary generate a magnetic field which induces a current flow
in the
> > secondary. I don't see how a seperate coil, located somewhere else, not
> in the
> > "plane" of the secondary transfers any energy over?? Am I mis-understanding
> > inductance?
> > 
> > Thanks,
> > Patrick.
> 
> 
> 
>