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Re: Shocking Secondaries Re: Weather/coil performance

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,

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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