Re: Coat the secondary or not?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Mr Gregory Peters <s371034-at-student.uq.edu.au> 

Michael,

Positives:

a) coating helps prevent the wire from sliding off the form (which does 
happen when the coilform shrinks in cold weather).

b) a thick coating protects the enamel insulation on the wire from being 
damaged when your neice knocks the secondary over.

c) coating insulates the coil, reducing corona loss, and allowing slightly 
(very slightly) higher coupling. Also, coated coils seem to suffer less 
damage when arc overs occur (if you cut the power quickly).

d) prevents dust from gathering between the windings, easier to keep clean.

negatives:

a) takes effort to coat a coil, though not much if you don't care how it looks.

b) theoretically increases rf losses, but not enough to notice.

c) theoretically increases inter-turn capacitance, but who cares when we 
use a massive toroid anyway?

d) makes repairs harder


Comments:

a) Any increase in rf loss or inter-turn capacitance is offset by the 
increased power handling ability of the coated secondary, besides these 
negatives are practically non-existant. Coated coils tend to handle arc 
overs better too, and you often can just give the arcing areas a light 
recoat to solve the problem.

b) If you coil conservatively, you will never suffer from racing arcs and 
so on anyway. Just be "gentle" when playing with coupling settings, and 
don't make big changes. Cut the power as soon as something goes wrong, 
before big carbon tracks form on the secondary. Then give it a light recoat 
to repair.



Conclusion:

just coat the damn thing :), for the sake of protecting the windings 
against damage by being dropped, and to hold the wire on there. Who cares 
about the rest? If you really care about a few watts (if it's even that 
much) of rf dissipation, you should start with teflon tank capacitors and a 
pseudospark gap (why aren't coilers using these yet?). :) :)

If you want to wind a secondary for short term testing, and have no 
intention of keeping it forever, don't coat.


Actually, now that I think about it, I can't remember if teflon is better 
at rf than polypropylene anyway.......


Cheers,

Greg.
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
Date: Friday, May 7, 2004 4:21 am
Subject: Coat the secondary or not?

 > Original poster: pepperman-at-softhome-dot-net
 >
 > I've read several opinions on whether or not you should coat the
 > secondary with some sort of sealant/protectant (e.g. polyurethane,
 > epoxy, etc.).  The pluses are that the coil is well-protected, and
 > possibly more attractive (depending on your feelings about what
 > looks good).  The minuses are that if you coat the coil, you can't
 > really get at it in case something goes wrong.
 >
 > What are the current opinions, for and against?  When would you
 > want to have access to the windings, and when would it not matter?
 >
 > Michael Johnson
 >
 >
 >