Re: Coil coating: (was Re: Fiat PVC, Fiat Lux)
Hi Reinhard, all
Are the raised (hot stamped) letters on PVC common practice in Germany?
Is this for water pipe? That must play havoc with getting the fittings
leak proof. The PVC I get, and assume most of the US, is only inked
with the vital statistics. The ink will wear off in the weather, and
doesn't conduct electricity (but looks bad).
I also built a motorized coil winding lathe. It took less time to build
the lathe and wind a coil than winding a coil alone would have taken. I
used a DC motor out of a large tape recorder (reel drive motor). I
hammer a piece of wood on the end of it, and turn a mandrel for the coil
form I am using. The tail-stock is a movable upright with a "T" nut and
3/8" bolt that fits the mandrels I turn on the drive end of the
"lathe." It seems crude (almost all wood) but works very well. I do
use it to apply coatings, but cover the bed with newspaper first. (I
wouldn't chance it with a good engine lathe).
We are probably arguing over semantics here. At the power supply
company I worked at, the transformer winding machines were called
"lathes," so that is what I call my TC secondary winder. Since it is
powerful enough to turn the mandrels it is also a lathe in the true
(cutting) sense of the word.
I wasn't on-line when I started playing with TC's. All my information
was from late 1800-1900's literature on the subject, so I did a lot of
experimenting and wound a lot of secondaries and primaries. I had seen
a toob driven coil when I was a kid, but didn't know anyone actively
building Tesla coils.
The best secondary wire I've found is silver-plated, "tefzel" insulated,
wire-wrap wire. My best (most efficient) coil is 15" long, 3-1/2" dia.,
wrapped with 31 AWG silver plated wire and no coatings. I did a nearly
identical coil with an epoxy coating and it didn't perform half as well
(but didn't see the same results with ordinary magnet wire). Coating
magnet wire doesn't seem to hurt performance to as great a degree. So
maybe the conclusion to be reached is: if the original wire insulation
is a poor dielectric, any additional coatings don't really detract as
much from performance. Use a good dielectric and it doesn't make sense
to add a poor dielectric coating?
The silver plated wire is expensive. I think I paid $28 for 1,000 feet
(enough for one secondary). Some lower cost wire-wrap wire barely
worked at all (it was supposed to be silver-plated, but it didn't look
I agree with you. Coating coils is the best way to do it, most of the
time. With careful electrostatic control and watching the spacing of
objects by the secondary, you can get a small performance boost by
leaving the wire uncoated. (and, unless you have unlimited transformer
power, small incremental increases in performance, are the name of the
game). Due to material constraints, and an unwillingness to have a pole
pig in my living room, I have to be happy with less . . . so every erg
counts. Most of the time I use the 200 watt OBIT, and only drag out the
KVA induction coil when I want to impress someone.
I was winding a lot of secondaries at one time, spaced turns, different
wire size, different wire types and different coatings. I don't think
it is necessary to give a lot of preparation to the PVC. I wash it with
water, air dry it, and wipe the outside with acetone. If it is dinged
up, I file it or sand it down first. I tried coating the inside and
outside before winding, and think it is wasted effort.
There does seem to be a great difference in PVC (here at least). I got
some thin wall 4" (high density) PVC for drain lines (for things like
garden soil drainage, not for building codes) that worked poorly and
some 4" PVC that was designed to meet building codes (low density
plastic, relatively thick wall) that worked very well. I also tried
some pipe designed for pressure (water delivery, not for drainage) it
was also "schedule 40" (ordinary residential plumbing use in the US) it
doesn't work as well as the low density pipe made for building code
drainage use. I sort of concluded that low density, or molecular weight
matters when it comes to performance.
I have to agree with the appearance of the epoxy coated and multicoated
varnished coils. I haven't seen any air bubbles in my finishes. I did
see a recommendation in a boat building article, that the resin be
sprayed with acetone to break any surface bubbles.
If one is to go to the (minor) expense and trouble of a motorized
winder, there seems to be little reason not to wind lot of coils and try
everything. The cost of wire and PVC is minor. It takes a few minutes
to chuck a new piece of pipe and spin a few hundred turns of wire on.
If you wreck one, so what? If you are building for demonstrations,
appearance or display, that's another matter entirely.
The only time I destroyed an uncoated coil was when I (like you) took a
hit between the primary and secondary. Any streamers that come off the
sides of a coil don't seem to have enough energy or aren't focused
enough, to burn the wire enamel.
Cotton covered? That stuff is scarce around here. I did see a few
spools of (very pretty green and yellow) silk covered magnet wire in an