Re: Coil coating

Hi Bob, all,

My comments interspersed below.

> Original Poster: Bob <misiura-at-nccoast-dot-net>
> 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).

For indoor sewage (i.e: toilet, bathtub, etc) we (germans) use PP
pipe. This stuff has a relatively thin wall thickness. The markings
on this kind of pipe are inked on only. The come in various lengths
and diameters up to 150mm (~6"). One end is rated diameter and
the other end is slightly larger (~160mm for 150mm pipe) with an
inner o-ring, so that you can join the next pipe directly w/o the need
for an extra coupling muff or glue). Our PVC pipe is used for outside
and underground sewage systems. The come in a variety of
diameters. I have seen up to 40cm diameter (~16"). They, too,
come with a rated diameter/integrated o-ring coupler. The size,
pressure rating, material (PVC) and some DIN numbers are hot
stamped and the companies name plus some numbers (maybe
stock or part numbers) are inked on. The hot stamped markings
do not run up all the way to the end. So, coupling them together
isnīt a real problem (no leakage). Once they are joined together
and left alone a few days, you almost canīt seperate them
anymore, because the o-ring *really* sticks to the joined pipe.
As a matter of fact, during my rolled poly cap tries, I needed a
hammer to remove the end caps of the PP pipe. The 20cm PVC
pipe I am using for my (almost) 8" coil is about 6mm thick. It
seems to be made of three layers. The outer and inner layers
are about 1mm thick, dull orange in color, and are NOT attacked
by acetone or nitro-thinner. The inner layer is about 4mm thick
and of a much lighter tan/orange color. This is soluable in
acetone (it becomes slightly sticky). The oringinal length of this
pipe was 2m and I cut it down to 106cm. The coupling muff (on
which I did not wind any wire) is around 13 (my lucky number)
cm high. I use a press in end cap on the integrated coupler side
to mount the coil to my coiling table. I did remove the o-ring, tho.
Otherwise I would never be able to remove this cap again. I
epoxied a (round peened) piece of copper (3mm thick) to which
I soldered an M6 (~1/4") nut and the lower end of the secondary
winding. This allows for a 100% tight (and tidy) RF ground

> 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).

>From the sound of it, I built something very similar. The real advantage
is, not only can you wind the wire with it, but you can leave it running
while coating the coil for a very smooth, sag and run free coating.

> 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
> powerful enough to turn the mandrels it is also a lathe in the true
> (cutting) sense of the word.

Okay, a misnomer. I was talking about my multi-thousand dollar
metal/wood turning lathe and mill. This isnīt something I would
want to "sacrifice" for a project. (This kind of stuff is real
expensive in Germany. For a 3-sided flip-over (6 cutting edges)
tungsten carbide triangle, I have to pay around $60 here in
germany a PIECE. I remember my dad buying them in packs
of 10 for a couple of bucks from Cross-Tools in CA, back in
1980-81. Lucky for me, my dad (as I) always bought/buy this
kind of stuff in large quantities, in order to always have spares
(something my mum never understands, but is glad, when I
can cover her needs ;o}).

> 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

Wow, Iīll bet. The silver plating will increase the Q of your coil
dramaticly. This trick is used in lots of RF equipment (any
kind of satellite equipment will soley use silvered wire for itīs

> (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
> 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?

True. I used normal double thickness motor/xformer winding magnet
wire to wind my 8" coil. However, 57" and an occassional 63" from
1275VA is A-Okay with me. My final design will run on 6kVA and
around 12-13J. I am hoping for at least 3m (118") sparks. From
what I am seeing now, I donīt think this will be a too much of a
problem ;o))).

> 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 like silver).

That ($28) doesnīt sound too expensive, I think. BTW: I HATE wire
wrapping technique. It really looks aweful!! ;o(( and changing an
already built circuit is a PTA.

> 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.

I think one advantage of covering the coil former on the inside,
is that you increase (due to an increase in insulation) the
breakdown rating. This may decrease the possibility of an
inside arc killing the secondary.

> 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.

Yes, I coated coil DOES look (which is a certain factor for
me) a lot better, than an uncoated coil. The resin, I used, was
slightly thicker than SAE-10 oil and remained that way for
~2hrs, after which it slowly thickend out and hardend within

> 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 antique store.

Yup. I got this stuff (way back in 1983) from a guy who used to build
telephones immediately after the world war. It was used to build the
bell and telco-line-xformer coils. It is bare copper wire coated with
a single insulation (beautiful red). The wire is then coated with
multiple strings of wound cotton thread. The final, outer, covering is
some kind of flexible yellow plastic (not PVC, tho). The guy gave
me two rolls, a 100m each, for free. Alas, I didnīt get around to
building a coil back in 1983, so the stuff ended up in my wire box.
When I finally got back to coiling during the last part of 1997, I
found the wire to be completely tangled up (probably due to my
various search methods, when looking for a piece of wire for
some project. I.e: take the drawer, dump it on the floor, pile
through it, find what is needed and dump the rest back into the
drawer ;ö]. So, all I could salvage (after about two hours of trying,
more unsucessfully than sucessfully, to untangle the stuff, was
enough for a 3.34" coil (I used an old fishing tackle rod container).
It did make a pretty good coil tho. With ~400VA input, I got ~60
cm long sparks. But even though this wire was really triple
insulated, it was shot by a single arc over between primary and
secondary. This experience led me to believe that coating a coil
is worth the extra trouble (for durability) and the experience with
my 8" coil (which suffered no damage) kind of undermines this

Oh, BTW: For more info on my 8" coil have a look at:


I partcipated in Shaunīs coiling survey. Or even have a
look at my homepage at:


Click the tesla icon for my TC page. This also shows some
pictures of my winding jig. The spark length pictures, etc are
outdated. When (??) I have some spare time, I will update
the pages. I still donīt quite like the looks of it anyway. If
interested, you can ponder through the rest of my site. If
you like HV, have a look at the memorandom I wrote for
my dad (his experimental plasma physics lab).

Take care and coiler greets from germany.