Re: Shocking Secondaries Re: Weather/coil performance

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>

Mike and all,

Getting "bitten" from a secondary is a Tesla Coiler's rite of 
passage. However, the phenomenon does not appear to be dielectric 
absorption as much as dielectric surface charging during coil 
operation. In my experience (using a 10" coil with a relatively thick 
Behr Build 50 coating), surface charges become stranded on the outer 
surface of the insulating coating while running the coil. After a 
run, you can easily feel the presence of these charges as they 
attract the hairs on the back of your hand and arm, particularly in 
the region near the top of the winding. As you move your hand or a 
grounded object closer to the surface, you can easily feel, and hear, 
the snapping of numerous static electric discharges from the surface 
of the coating. These little discharges can easily jump an inch or 
two, so the surface potential must be quite high (~50 - 100 kV). BTW, 
these charges also act like dust magnets, attracting microscopic dust 
and debris that slowly coats the top of the coil over time.

During a run, surface charges are developed through corona surface 
charging or perhaps via partial discharges between regions of the 
secondary (precursors to racing sparks). After the run, these charges 
remain, stranded on the non conducting surface of the dielectric 
coating. Assuming that you're insulated from ground, if you then rub 
your hand along the surface (to form half of a capacitor versus the 
grounded winding) and you then touch the toroid, you'll get a VERY 
nasty shock. If you then quickly remove your hand and again touch the 
toroid, you'll get another, smaller, jolt from inductive (re)charging 
of your body. I suspect that thicker coatings may show this effect to 
a greater extent.

The charged coating behaves much like a charged electret (or 
electrophorus). Surface charges on a good dielectric become 
temporarily trapped and are very difficult to completely neutralize 
without the use of an ionizer. Depending on the insulation resistance 
of the coating material, these charges may take many hours, or even 
days, to decay.

BTW, to prevent getting zapped when handling or moving a secondary, 
temporarily connect yourself to one end of the secondary to prevent 
accumulation of charge between you and the secondary. You still may 
feel the little discharges coming from the surface of the coating, 
but at least you'll prevent a "big zap" that could cause you to jerk 
and possibly drop the secondary.

Best regards,

Bert
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Tesla list wrote:
> Original poster: Mike <megavolts61@xxxxxxxxx>
>
> I read about those super caps needing to be charged and discharged once
> before they really work well.   The term I recall reading about was
> called dielectric absorption.   Could this be the same phenomenon that
> is occuring in the pvc and/or coating on coils that are shocking
> people?   I have felt a little static on my coils in the past, but never
> been shocked to any serious degree.
> Mike
>