Re: straight core transformers and chokes

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

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


A lot of these old induction coils used #36 or 38 awg on the sec. winding.
I would forget about the wax impregnation and just drop it directly into a
small fiberglass oil tank -- much better insulation with no voids to
breakdown the sec. winding.

Primary winding was #10 AWG.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, September 02, 2003 1:47 PM
Subject: straight core transformers and chokes


 > Original poster: dgoodfellow-at-highstream-dot-net
 >
 > I am contemplating the construction of a straight core transformer. I read
 > an old Tesla coil how-to book from the 20's that was on microfilm in the
 > New York public library a long time ago. My hand written notes from 20
 > years ago are as follows:
 >
 > "Pieces of 18" long #20 or 22 B&S gauge iron wire, stuff as many as will
 > fit into an iron pipe less than 2" in diameter. Throw into a coal fire and
 > leave until it dies out. Remove iron wire, clean, and coat individually
 > with shellac. Push back into pipe, then push out the bundle slowly, wrap
 > with cotton bandage, 1" wide, and coat with shellac.
 >
 > The builder was to then create a number of thin wooden discs 6" in
 > diameter, with a hole cut in the center large enough to slide them onto
the
 > bundle of iron wire. The primary and secondary windings would be wound
 > between the disks. The disks are to be 3 1/4" apart along the bundle of
 > wire. The transformer would have 4 sections, each 3 1/4" wide, with a 1"
 > gap in the center, between the 2 primary windings and the 2 secondary
 > windings. Just imagine 4 donuts stacked on a paper towel roll and you get
 > what this is to look like.
 >
 > "Primary is wound in 2 sections with #12 B&S double cotton covered wire, 2
 > 1/2 lbs. Wind 60 layers, with a turn of paper between each layer."
 >
 > The next section is made essentially the same. For some reason, I didn't
 > write down the gauge of the secondary wire, or how many turns were
 > required. I do remember that it was a lot of layers.
 > The book claimed that a straight core was superior to a closed iron core.
 > This, I wrote down word for word...
 >
 > "A straight core is always best to use; for on the fall of the current
from
 > its maximum value to zero, the magnetic flux falls from its maximum value,
 > not to zero, but to a value which depends on its residual magnetism. The
 > residual magnetism in an open circuit is much less than in a closed
 > magnetic circuit so that when the current suddenly becomes zero, the
 > magnetic flux drops lower in an open circuit than in a closed one. As the
 > electromotive force in the secondary is proportional to the fall in the
 > magnetic field, it is greater with a straight core than with a closed
 > circuit of iron"
 >
 > So here's my plan.... I see that Mcmaster Carr sells iron wire, in 1 foot
 > lengths, or rolls. It is high carbon wire. I want to take a bundle,
varnish
 > each piece, stuff it into a thin walled phenolic tube, cut the wooden
disks
 > which will divide the primary and secondary windings, and start winding a
 > transformer.
 >
 > I would like to hear from anyone that has knowledge of transformer design
 > parameters to evaluate this, and submit your thoughts on this type of
 > transformer before I start building it. Any guess on the gauge of wire for
 > the secondary? How many turns?
 > Does anyone recognize this book? It was titled something like "How to
build
 > and test a complete Tesla coil" It also described the construction of a
 > high voltage rectifier by filling a fish tank with battery acid and
sinking
 > an array of plates made of iron and aluminum,  similarly to a car battery.
 >
 > Thanks to all who reply,
 > Dave Goodfellow
 >
 >
 >