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Secondary Coil Electrostatic Charge

Hello Everybody,

I am Robert Stephens and new to this group.  I've been following your 
mail exchange for the past week with interest.  The subject of 
electroststic charge being deposited on the surface of the TC 
secondary winding has been an interesting topic of discussion over 
the past few days.  I see that several of you now have surmised the 
correct mechanism of storage of this charge (dielectric polarization, 
and to a lesser degree static surface charge of the insulation on the 
secondary windings), but can anyone explain WHY an alternating 
current high voltage source like a TC can charge dielectrics 
(capacitors) just like a Van de Graaff generator?  

The first person to correctly describe the mechanism of this effect 
will win an all expenses paid trip to the head of the class!

On a related note I will share some of my own observations.

-a properly coupled TC with a well designed top load terminal, even a 
large coil driven to multi megavolt levels will have hardly any 
secondary residual surface charge after a good run.
-an overcoupled secondary will develop firecracker hot areas of 
surface charge in a specific zone, or zones along its length.  This 
occurs in those areas where the coil will begin to arc across its own 
windings if pushed hard enough.

Someone just suggested winding the secondary on an air form.  I 
suggest that the dielectric polarization which is occuring on the 
OUTSIDE of the secondary winding in the O.D. of the insulation is 
also occuring simaultaneously on the INSIDE DIAMETER within the I.D. 
of the wire's insulation and also in the plastic tube on which the 
wire is wound.  The wire conductor itself forms an effective Faraday 
shield which will serve to isolate the O.D. and I.D. zones.  
Discharging the O.D. zone will have little effect on the charge held 
in the I.D. zone.  These two zones are in fact two discrete 
capacitors connected in series with  a common center terminal being 
the wire.  I suggest that as long as there is a dielectric coating on 
the wire with a dielectric constant greater than that of air (1), 
even if the wire was stiff enough to self support without a form at 
all, we will still see this charge effect.

Here is an illuminating experiment which is easy to conduct.  I did 
it with my single 15KV, 60MA neon powered coil in my living room and 
used the side of my fridge as a conductive ground plane (if you use 
an appliance, ground the case to the same circuit that grounds the 
bottom of your secondary, or at the very least unplug the appliance 
from the mains or you could smoke your compressor because the high voltage
which will be applied to the cabinet will seek  the ac mains as a 
ground through the motor insulation).  Place a  grounded vertical 
sheet of metal or fridge at the edge of your coil's striking 
distance.  Hang a large piece of paper (I used a 2x3 foot poster 
calender) against the surface of the ground plane with a magnet or tape and support it 
so that it has a 1/4 to 1/2 inch air gap between itself and the 
ground plane.   Fire the TC for several seconds and then turn it off. 
 You will see the paper suck itself flat against the ground plane and 
hold there with powerful electrostatic attraction.  Peel it off and 
you will hear it snap and crackle.  Run the back of your hand on the 
surface of the paper and you will get sufficient charge from merely a 
few square inches to receive a mild shock!  IF YOU TRY THIS SAME 
EXPERIMENT WITH A VAN DE GRAAFF GENERATOR INSTEAD OF THE 
SPARK GAP DRIVEN T.C. YOU WILL GET EXACTLY THE SAME EFFECT!

The answer to this phenomenon is hidden in the term DAMPED SINUSOID.  
There, I just gave it away.

Happy coiling,
Robert W. Stephens
Director, Special Projects
Lindsay Scientific Co.