David, You may have missed my point. My point was not to have too many
turns in the primary, but to have the proper amount in the most compact
space. For instance having a 7" center hole and needing 9 turns the primary
will be 6+ inches wide, but with 3 turns stacked it will only cover 2
inches of the secondary and be 2 inches high. But I don't know what effect
having the coils in a "boxed" config. would produce.
Doug
On Mon, Oct 19, 2020 at 11:28 AM David Thomson <aetherwizard@xxxxxxxxx>
wrote:
> My experience with bipolar coils (or any coil) is to design the system such
> that the primary is as close to 1 turn as you can.
>
> It doesn't matter if you have multiple turns in a solenoid, or multiple
> turns in a flat spiral; you will have the same problems either way.
>
> What you want is to make the signal from the primary to be a single damped
> pulse, and eliminate the sine wave in the primary. It is the sine wave with
> multiple peaks in the primary that drags down the resonance of the
> secondary.
>
> David Thomson
>
>
>
> On Thu, Oct 15, 2020 at 6:52 PM Douglas Johnson <doug379306@xxxxxxxxx>
> wrote:
>
> > Thank you both, I think I know where to go from here on my current build.
> > My project is a larger bipolar than I have built to date. Secondary is
> 3.5"
> > dia. X 24" with .015 mag wire. By the time I built the primary it was 6"
> > long and I was getting "runners" on the secondary. I think my fix will be
> > going to a flat spiral primary.
> > Doug
> >
> > On Thu, Oct 15, 2020 at 12:06 AM jimlux <jimlux@xxxxxxxxxxxxx> wrote:
> >
> > > On 10/14/20 6:34 PM, Gary Lau wrote:
> > > > It also needs to be said that highest coupling is not the goal - more
> > is
> > > > not necessarily better. Performance will generally increase with
> > > > increasing coupling, until an ill-defined threshold is reached.
> > > Increasing
> > > > coupling beyond that point will result in what's called "racing
> > sparks" -
> > > > sparks across portions of the surface of the secondary coil that can
> > > > quickly destroy the secondary. You need to design the coil in such a
> > way
> > > > that the distance between primary and secondary can be experimentally
> > > > adjusted to vary the coupling, typically by raising the secondary.
> For
> > > > most coils, using a flat spiral primary provides adequate coupling
> when
> > > the
> > > > plane of the primary is near the bottom end of the secondary.
> > > >
> > >
> > > ANd the flat primary also serves as a sort of counterpoise to make the
> E
> > > field uniform between topload and primary.
> > >
> > > Go back in the archives and you'll see all sorts of primaries,
> > > solenoids, inverted cones (I did that one), and flat spirals.
> > >
> > > The advent of modeling tools (like Inca and JavaTC) that could
> > > *calculate* coupling and fields pretty much drove the "make it flat" -
> > > except for ones requiring high coupling (DRSSTC, for instance), where
> > > solenoid primaries are popular.
> > >
> > > There's not much you can do with a conical primary that you can't do
> > > with a flat or solenoid, with some control of the spacing.
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