Re. Strange events and me coil unexplained

To: tesla-at-pupman-dot-com
Subject: Re. Strange events and me coil unexplained
From: Gary Lau 16-Dec-1998 2100 <lau-at-hdecad.ENET.dec-dot-com> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Thu, 17 Dec 1998 11:29:34 -0700
Approved: twf-at-verinet-dot-com

>Original Poster: "Paul Marshall" <klugmann-at-hotmail-dot-com> 
>
>Hey everyone,
>   Last night I ran my 6.5" coil at approximatly 5 Kw. 14.4 Kv. My air 
>choaks melted. They were wound with 18 AWG insulated wire. Even the PVC 
>core melted and twisted. How is this possible, there should only be 
>millamps on the HV side ? My capacitance has also increased. I made 
>these caps over a year ago. Each cap is .026 uf. I have 4 in the 
>circuit, two each in parallel and then these two circuits are in series. 
>Ordinarly I'm taped out with the large top load at the 13 th. or 14th. 
>turn. Last night I had to tap in to the 9th. turn ! A few weeks ago I 
>move the coil outside and noticed that I had to tap in. I attributed 
>this to ground clutter. Could the caps still be setteling ?
>The calculated value of these caps were .026 uf. They had a measured 
>value of about .024 uf. They are poly plate caps. Does anyone have 
>anyone have any ideas about the RF choaks or the the caps ?
>
>thanks,
>paul m

Filter chokes in a Tesla Coil develop HUGE voltages across them, and
depending upon the rest of the filter topology, may ring at the Vpri
voltage for quite a long time at each bang.  If the PVC form either
permits arcing between the coil ends, or you used multiple, less than
incredibly well insulated layers, there will be arcing, and arcing begets
more arcing, and melting.

Is your belief that your cap value changed due just because the primary
tap required for resonance went from 13-14 indoors to 9 outdoors?  (Did I
read that correctly?)  I believe that when operating outdoors where there
are always air currents, the currents remove the cloud of ionized air
surrounding the top load, reducing the secondary's effective capacitance,
so you'd have to lower either the primary C, or in your case, L, to
maintain resonance.  There was a thread on this List several months ago
debating whether this explanation was valid, I don't recall the final
consensus.

Regards, Gary Lau
Waltham, MA USA