Re: mini coil

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Finn Hammer <f-h@xxxx>

My thinking on this subject:

Plastic is heated by RF, when it is subjected to an electrical field, not 
to a magnetic field. This means when it is used as a dielectric to separate 
potentials, not just because it is sitting inside a coil.

Look at the secondary former: The electrical field is lengthwise on the 
coil, means, one end grounded, the other alternating at extreme potential. 
So: what we really ought to worry about is a short coil, since it will be 
stressed more than a long one, potentials equal. However, the field 
strength is orders of magnitude lower than the breakdown field strength, 
measured along the length of the coil. Radially outwards, from coil center 
to surroundings, the field is even, so there is no dielectric action in 
that direction.
A couple of numbers:
Dielectric strength of PVC: ~300V/mill -> 300.000 V/Inch -> a 20 inch slab 
of PVC is good for 6MV, but a 20 inch long tesla coil probably only 
produces about 300-400kV.
I think this is the reason we get away with using PVC as a secondary former 
in the first place: no particular dielectric stress at all, as opposed to 
in a capacitor, where PVC would fail miserably, along with polyester 
(mylar) another famous insulator.
Well, due to MMC`s, thanks all!, we don`t have to worry about that anymore.

I wish you all a happy new year, and DC a continuing recovery.

Cheers, Finn Hammer

Tesla list wrote:

> Original poster: "claudio masetto" <claudmas@xxxxxxxxxxxxxxx>
>
> I am thinking of making a mini coil with a secondary of 2.375" x 12" pvc 
> pipe. It has a fairly thick wall of about 3/16". Would it make much of a 
> difference in performance if I use a thinner wall pvc pipe.
>
> Thanks
> Claude.