# RE: 3 Coil System Was: A photographic tutorial of PancakeCoilwinding...with movies...(fwd)

```---------- Forwarded message ----------
Date: Sun, 24 Jun 2007 10:50:42 -0500
From: David Thomson <dwt@xxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: 3 Coil System      Was: A photographic tutorial of
PancakeCoilwinding...with movies...(fwd)

Hi Bart,

> >I disagree.  In the case of a solenoid secondary, yes, it is necessary
> >to run a transmission line to the third coil to avoid inductive coupling.
> >However, a flat spiral coil has its magnetic field tilted 90 degrees
> >out of phase with a thin solenoid connected to the center terminal.
> >There is no inductive coupling at all.
> >
> I'm not following your logic. In the case of a standard 2
> coil system using a flat archimedes spiral primary and a
> solenoid secondary, the coils are inductively coupled. Can
> you clarify for me?

If the flat spiral coil winds all the way to the center of the circle, then
the magnetic flux lines tilt 90 degrees from its angle just inside the first
few percent of the outer windings.

In the case where a spiral primary couples to a solenoid coil, the spiral
primary does not wind all the way to the center.  The angle of the magnetic
flux lines are pretty much in phase with the solenoid coil.

You can easily verify this by applying a DC current to a full wound flat
spiral and follow the magnetic field curvature with a permanent magnet in
your hand.  Of course, this obvious since we know the magnetic field is a
toroid with a hole that passes through the center of the flat spiral.  The
curvature of the toroid from the outer winding toward the center of the coil
is 90 degrees.

At the outer windings, the north south polarity is parallel to the flat
spiral plane.  At the center of the coil, the north south polarity is
perpendicular.  The outer windings of the flat spiral tend to squeeze the
base of a solenoid place in its center, like milking a cow.  However, the
inner winding of the flat spiral pushes up and down, which is why it creates
a longitudinal effect when a coil is placed in its center.  Inductive
coupling takes place with the squeezing effect and capacitive coupling takes
place with the up and down effect.

Putting a thin solenoid coil in the center of a fully wound flat spiral
causes capacitive coupling only.  There is no inductive coupling.

> >As you have demonstrated to me (intentionally or not), capactive
> >coupling is the means for driving the third coil in acoustic mode.
> >
> Unintentional. The acoustic mode you are theorizing is not
> something I understand.

I hope maybe I have explained my understanding of it above.

> >Many magnifier coilers have found that in order to get sparks out of
> >the third coil, they actually have to be untuned.  If the
> third coil is
> >perfectly in tune with the secondary/primary system, standing waves
> >develop in it that have a high potential at the top load,
> but no current.
> >
> L3 is not magnetically coupled in standard magnifiers, but
> they are electrically connected. The primary of the driver
> must be tuned to the combined inductances of the L2 driver
> and the L3 extra coil. What appears to be "untuning" is
> nothing of that nature. The added inductance of L3 will cause
> the primary to be tuned to a lower frequency. So, they'll end
> up increasing primary inductance or change the capacitance to
> suit. Regardless, it's tuned (won't do well if it isn't).

I think Jeff has demonstrated that this is not the case.  His flat spiral
coils have an arbitrary length brass pipe as the third coil.  His coil
produces streamers because the third coil is not tuned with the
secondary/primary system.  This means there will be current at the top of
his brass tube.  Where there is current, there is a steady stream of
electrons.

The high potential of the system knocks the electrons into the potential
gradient around the top load and causes streamers.  If the third coil were
completely in tune with the primary/secondary system, there would be a
perfect standing wave in the third coil.  This means there will be zero
current at the top load, and thus there will be no streamers, as in my coil.
My tall solenoid coil was apparently close to being at the third octave of
the primary/secondary system.

Thus there was a node of zero current near the top load.  My system was
probably slightly out of tune, however, in order to get the type of
discharge I photographed.  If the system had been perfectly in tune, there
would likely have been nothing there but a strong electrostatic field.  And
there was a strong electrostatic field around the coil as it was.

> >Jeff also seems to be seeing the same thing when he removes the
> >brass tube.  If he were to try brass tubes of different lengths,
> >he will find the streamers actually disappear as the tube becomes
> >resonant with the primary/secondary system.  When the tube is
> >exactly in tune, he will get no streamers at all, but will likely
> >get the standing wave coronal discharge I got on my system.
> >
> I disagree. The tube will capacitively load the coil out of
> resonance "if" the coil is tuned without the tube in place.
> Tuning must occur after everything has been fully assembled
> and in position. If he were to add a longer or larger tube,
> he would be required to retune the coil to it's new resonant
> frequency.

You are correct.  If you build the system one way and change the parameters
part way through, it will have to be retuned.  What I am talking about is
the final tuned system, for whatever frequency it is tuned to.  If the L1:L2
system is resonant with the L3 tube after everything is working, there will
be no discharges and only a strong electrostatic field.

> Well, not in my experience. My 3 coil resonant transformer
> had all 3 coils tuned to resonance with each other (they were
> all matched in frequency) and it produced streamers just fine.

Do you have details available?  Can I see the setup from a photograph?

> >I don't see how L3 will no longer be seen as a capacity just because it
> >is in resonance.  I think what you mean to say is that L3 will not
> >produce streamers when all three are in resonance.
> >
> I'll try to clarify. First, of course there is a capacity
> with L3. What I intended to get across was that L3 would not
> be seen as only a capacity. When L3C3 are resonant with the
> other two coils, then (and only then) do we have a 3 coil
> resonant transformer capable of higher potentials. We are
> also capable of higher coupling between L1:L2. L1 is tuned to
> the combination of L2 and L3 combination resonant frequency's.

None of this indicates there is ever any inductive coupling between Li:L2
and L3.  The only way L3 can couple is through capactive coupling.  As such,
L3 must always be seen as a capacity to L1:l2 and nothing more.

> In my experience, the magnetic field lines of the flat coil
> "will" intersect the solenoid and there will be inductive
> coupling. Tell
> you what, I can measure this with my small closewound flat
> coil and a 2"
> solenoid about 9" tall. I'll report back the coupling.

I'll need to look at this to see if it modifies my own understanding.  Let
me know the results.

> It [JavaTC calculations] can get a little complicated and it's slow
> (that's the downside).

It takes 18 seconds on my duo core processor.  I can wait. :-)

Dave

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