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Hi Kurt,

I am very familiar with making electrets.  I have made several, more
typically in the form of a capacitor using polycarbonate as a dielectric.  I
place the capacitor in an oven, and raise the temperature to the glass
transition temperature, then putting a potential across the dielectric while
letting the capacitor slowly cool.  Electrets work either by charge trapping
(monopolar) or by bending of polar molecules (bipolar), or both.  I believe
I recall that charge trapping is generally considered less stable of the two
mechanisms.  Most technicians I have talked to are familiar with this
effect, and are leery of filter capacitors that do not have shunts in place.

But I digress.

Yes, most likely it is due to "coronal rectification," or something like it.
I find it interesting that often when I operate a coil, initially there are
several strikes to the ground rail.  After a few minutes, however the number
and frequency of the strikes diminish.  I assume that this is some sort of
electrostatic effect.  Perhaps this is when the parasitic charge is building
up in the dielectric. Undoubtedly, this is due to "coronal rectification."

Has anyone had this effect of static build-up on the surface of the coil
when operating the coil indoors?

I suppose that an Earth potential effect is wishful thinking on my part.  I
recall reading that the ionosphere has about one Terawatt of power
available, and that there is about one hundred Volts per meter potential
difference as a result of the selective filtering of the Earths magnetic
field.  It is a good thing that air is a good dielectric, give 100V/m I
would be in trouble if the contrary were true.  On the other hand, if you
could tap into the Earth's ionosphere, a Terawatt of power would be yours,
albeit extremely high potential.

Best wishes,


On 6/4/12 5:18 AM, "Kurt Schraner" <k.schraner@xxxxxxxxxxx> wrote:

> I had several (fairly painful) shocks from my "Black & White" coil, several
> 10 minutes after operating it. My most plausible explanation of the effect
> ist the one of "electret" effect, mentioned several times on this list (-->
> archives!), and not something between earth and ionosphere. May be, the
> formation of the effect is realized by coronal rectification, which you
> mention in your posting, ant which is taking place in TC discharges. Please
> see:
> http://en.wikipedia.org/wiki/Electret
> BTW: B&W secondary is insulatad by 10 layers of polyurethane.
> Kurt
> -----Ursprüngliche Nachricht-----
> From: Peggy Day
> Sent: Monday, June 04, 2012 3:17 AM
> To: Tesla Coil Mailing List
> I've experienced the same ever year when I run my coil outside during
> Halloween.  Currently, the coil I'm using has about a 1/4 inch of epoxy
> coating the surface.  Even after 1/2 hour or more after a Halloween run, the
> static build-up on the surface of the coil can be startling, if you are not
> prepared.  This happens year after year, and is independent of what coil I
> happen to run.  I always find it a bit odd, given that the humidity around
> Washington DC is usually fairly high.  I would expect the charge to bleed
> off quickly.
> I always wanted to know if it was always the same polarity or if it was a
> positive or negative charge.  Possibly more important, why is there a
> residual parasitic charge?  I speculate that it is due to the fact that the
> Earth is charged with respect to the ionosphere, though I suppose that it
> could also be a residual parasitic charge resulting from coronal
> rectification, whatever that is.  I also wonder if other people experience
> the same when they run coils indoors, or is this just something that happens
> when outside?
> Mike
> On 6/3/12 5:09 PM, "Tesla" <tesla@xxxxxxxxxxxxxxx> wrote:
>> Yes a real phenomenon
>> Have received one good fright from static left on the surface of the
>> secondary after use. Left coil for 10 min before disassembly and got a
>> static shock off it after carrying it.
>> Secondary is coated with polyurethane and is on 25 cm PVC tube
>> ted in NZ
>> --
>> -----Original Message-----
>> From: ED
>> Sent: Monday, June 04, 2012 1:42 AM
>> To: Tesla Coil Mailing List
>> One of the subjects he
>> investigated was the charges left in the insulation on the surface of
>> TC's after operation and I'd like to repeat his tests.
>> _______________________________________________
>> Tesla mailing list
>> Tesla@xxxxxxxxxx
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