Re: General Questions

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 4/9/01 5:48:40 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

<< 
 >This "quite well", as I could verify, is that Araldite is a bad
 >insulator,
 >almost useless for electrostatics. Just a bit better than dry wood.
 >For Tesla coils, the presence of some glued parts close to the coils
 >is not a great problem. A coating of the secondary with this material
 >may be a bad idea, however.
 >By the way, Nylon is a similarly bad insulator, maybe worse. After
 >some bad experiences (have you seen what should be an insulator
 drawing
 >sparks?) I don't use it in anything involving high voltages.
 
 
 This observation with epoxy is intriguing, especially as I'm sure some
 on the list have used epoxy coatings on their secondaries!
 
 I can understand nylon being very poor, as it will typically take up
 2-3% water, and especially in the all-important surface layer.  This I
 can get my head round easily, as nylon is chock full of polar
 polyamide groups, but epoxy is pretty well devoid of anything polar.
 
 I wonder if the conductivity problem with epoxy is due to residual
 byproducts from manufacture?  Typically an epoxy is made from a
 mixture of a sodium salt of a bisphenol plus epichlorohydrin.  This
 means that the resulting resin as made contains common salt, which is
 supposedly washed out in the purification process.  I'm wondering if
 there is sufficient sodium chloride left behind in what you get sold
 to explain this conductivity problem.  It could be . . . I know that
 the epoxies used in the electronics industry have to be specially
 purified to eliminate lead corrosion in the packaging of ICs etc and
 that these resins are expensive for that reason.
  >>
-snip-
I recently re-wound my small 3.0" secondary after damaging it while testing 
my new sync rotary gap.  I used the same former and the exact same number of 
turns, with the same wire.  Everything else in the coil set-up is the same as 
before, and the new coil produces sparks an inch or two less than before.  I 
had originally used three coats of polyurethane and this time I used one real 
thick coating of pour on epoxy.

Ed Sonderman