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Re: Secondary Coil Electrostatic Charge

Date:          Tue, 19 Mar 1996 08:37:50 +0700
From:          tesla-at-grendel.objinc-dot-com
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Subject:       Re: Secondary Coil Electrostatic Charge

>From jim.fosse-at-bdt-dot-com Tue Mar 19 01:18 MST 1996
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Mar 1996 21:47:30 -0700
From: jim.fosse-at-bdt-dot-com (Jim Fosse)
To: tesla-at-grendel.objinc-dot-com
Subject: Re: Secondary Coil Electrostatic Charge
Date: Tue, 19 Mar 1996 04:27:50 GMT

tesla-at-grendel.objinc-dot-com On Mon, 18 Mar 1996 08:32:03 +0700, you
wrote:


>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?
>
[snip]
>-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.
>
YES, I've observed the same - 10 hemisphere => charge 28" toroid => no
charge.

[snip]
> 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.
>
Robert,
        Given a damped wave form: at some point, the damped waveform
is to weak to cause a discharge. That leaves the previous half cycle's
charge on the object.

        jim

>>Jim Fosse,

>>You're almost there, but it has nothing to do with an actual
>>discharge (corona).   That first 180 degrees of the big whallop that
>>comes off the top of the TC (corona or not) goes either positive or
>>negative depending on when you look at it in reference to the
>>charging polarity of the system capacitance.  Let's say it goes
>>positive +100%.  During the second 180 degrees of the first RF cycle
>>it will swing negative,  but since we're dealing with a 'damped
>>sinusoid' it has already diminished in amplitude, so it goes negative
>>say only -70%, it then goes positive again maybe to + 40% and then
>>negative to -20% and then quickly dies out.  That big initial whallop
>>of +100% followed by an opposite or partially cancelling -70% high
>>voltage waveform leaves a residual DC charge on dielectrics in its
>>immediate area.  If that 100% represents 1 megavolt (easily achieved
>>with a modest 15KV 120MA neon powered system), then that +30%
>> residual is 300,000 volts DC!  At these kind of voltages even the
>> microscopic capacitance represented by a small section of plastic
dielectric
>> on the outside of the secondary winding  can store enough charge to give
>>a person a nasty shock!
>>Note that a vacuum tube powered Tesla coil which operates in CW,
>>generates a continuous wave train of equal amplitude, SYMMETRICAL RF
>> sinusoids and that this type of TC does not demonstrate this residual DC
>> static charging effect, on its own secondary or on nearby surfaces.

>>Happy coiling, R.W.S.