Bipolar disorder - part 1

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Parpp807-at-aol-dot-com>

Hi all,

Terry has posted 11 pictures of my bipolar coil(s) at:

        http://hot-streamer-dot-com/temp/RalphsCoil/
  
I got interested in the Horizontal BiPolar TC from the large 
coil that was in the Chicago,
Museum of Science and Industry many years ago. The 
HBP TC was the way to go for me because I did not want 
errant sparks flying around my basement . I thot the HBP
would confine the sparks to between the ends of the coil. 
I found out that's not
quite true.

The power supply is a bank of 4 parallel NSTs for 15 kV 
at 0.150 mA. I have Terry's
filter circuit and I use around 50 uF of power factor 
correction. A 22 Amp variac
connects to a 120V / 30A dedicated line.  The MMC is 2 
separate strings of 15 GE snubbers, 0.33 uF -at- 2000 VDC, 
to give two outputs of 0.023 uF -at- 30 kV each. 
The GE poly snubbers are very good. A few have died trying, 
but on the whole they perform well. One of the Fair 
Radio 0.10 uF at 100 kV cracked open and bled its guts 
all over my bench top. That's when I learned the Fair 
Radio caps are mylar. I have several C-D KVX pulse 
capacitors in different values. These things are ruby
 mica. The C-Ds are pricey but they work well. All the 
primary solenoids on my coils are wound with 3/16 
inch soft copper. 
The 3/16 tubing is easy to work. It does not get warm 
at this power level.

My first coil is shown at BP 1 jpg.
My first born is 20 inches of # 22 wound on a 3 inch 
form. The pvc end caps are supported on wooden 
(yes, wood) supports around 15 inches above the 
nearest nail. The primary 
can be moved laterally along the slit in the plastic 
base seen at the bottom. The rabbit ear
antenna is #6 solid copper swiveled in stud-type 
binding posts. 3/4 inch diameter brass
balls are at the ends of the rods. The coil is wrapped 
with silicon rubber, and the rods are covered with 
Teflon tubing. The Teflon reduces the corona from 
the bunny ears. I learned that just brushing on some 
polyurethane will reduce the coronal discharge. With 
the antenna opened to its full spacing of 20 inches, 
the coil produced a nice white spark across the full 
distance of the coil. At the high
voltages produced at this wide gap, I got arcs and 
carbon tracks down the wooden sides headed for 
the nearest nail 15 inches below the coil. 

It's back to the drawing board.
I wanted a larger spark and I wanted to see if it is possible to have
 a HBP TC throw a spark longer than the physical size of the coil. 
In other words, as the voltage at the ends of the coil increases with 
the separation of the antenna, can a coil be designed to exceed that 
distance, or will the spark always occur between the shortest 
distance--the physical length of the coil? 

I decided to wind 48 inches of # 28 on a 4.5 inch OD form. 
This coil is shown in pictures BP 2 jpg and BP 3 jpg.
 My original plan was to support the secondary at the ends 
on vertical uprghts of  1/2 inch Delrin sheet. John Freau 
suggested that the best insulation would be to to leave the 
ends free and support the coil on a pedestal base as shown. 
The idea for the pedestal base is John's; the design of the 
base is mine. Please address all flames accordingly.  :-))  

The DC resistance of  the coil is 250 Ohms.
Ls calculated from Wheeler is 123 mH. Measured with 
a B-K 878 LCR bridge, Ls = 110 mH. Cself = 3.5 pF (calculated)
Using a signal generator, counter and oscilloscope, Fr = 256 kHz

The secondary is mounted on a section of 3/4 OD Delrin tubing. 
The 1/4 inch center hole thru the tubing was tapped at one end 
for a 3/8-16 Nylon bolt. There is a 1-inch gap between the two 
halves of the coil where the connecting
wire passes over the.gap. In this space I drilled a 3/4 inch hole 
for the tube to pass thru the center of the coil form and shoulder 
aganst a 3/8-inch hole at the top where the 3/8 -16
Nylon bolt holds the secondary to the tube. This arrangement 
shows clearly in BP 3 jpg.

The primary solenoid is shown at BP 4 jpg. The coil is wound 
in two sections and joined at the center where it attaches at the 
bottom to the center post. The entire coil is 16 turns,
spaced at 1/2 inch, OC. The diameter is 14 inches. I discovered 
a good method for winding a helix of this large diameter: I got a 
large roll of 12 inch roof flashing. The roll is springy, it unwinds 
itself and can be set to any diameter and then taped with duct 
tape to hold it at whatever diameter you set. I clamped the roll 
of flashing into a vise and used two-sided scotch tape to hold 
the coil spacers in place. When the coil was wound I used 
Nylon 6 - 32 screws to fasten the top half of the coil spacers 
so all I had to do was slide the fnished coil off of the form. 

The rabbit ear antenna rods are 1-inch aluminum tent poles 
that I bent and kinked around a large paint bucket. Thick 
walled vinyl tubing covers the rods. 
Any insulator, including polyU, will reduce the corona, but 
learning is very slow and nothing is going to save this 
beast  from the sparks flying out of  the right-angle pipe 
tees best shown in BP 5 jpg. 

PVC end caps one size too small are slipped into the 
ends of the secondary form and held in place with 
Nylon 6-32 screws thru the secndary form and drilled 
and tapped into the end caps. I am using the thicker 
schedule 40 pvc. Each end cap has a 4-inch 1/4 x 20 
brass bolt protruding outward from the center of the cap.
The end wire is wrapped around the bolt on the outside 
of the end cap. The brass bolt is the mounting stud for 
the rabbit ear antenna rods; it is going to have to hold a 
lot of weight,  and torqing of that stud became a problem. 
I used lock washers on both sides ot the bolt head and 
muscled down real hard to dig the stud into the pvc. 
Turns out that the sked 40 pvc takes compression very well.

BP 5 jpg shows the end arrangements with the mounting 
stud coming thru one of John Freau's toroids. This is 
about where my education in HV construction techniques 
really starts. Everything I know I owe to John and to Malcolm Watts. :-))
My goal is to get a spark larger than the length of the coil, 
in this case, 48 inches.The rods have to leave the coil on 
the outside of the toroid and be free to rotate to extend the gap. 
There is a piece of brass tubing inside the tee that telescopes 
tightly into the aluminum bunny ears. Electrical contact is made 
via a 1/4 x 20 brass screw passing thru the brass tubing 
and contacting a coupling nut on he end of the brass
mounting stud. The coupling nut is inside the vertical part 
of the tee (horiz in the pic)and the brass screw is 
accessible thru the hole in the tee. This hole also 
provides a convenient exit for corona. 

The brilliant engineering just narrated is going to be 
more than made up for by the poor 
electrical performance of this beast. The basement 
has a 10-foot ceiling with all the usual
infrastructure: conduit, speaker, phone, and TV lines 
running between the joists.
The rabbit ears are each 3 feet long rising to around 
two feet above the secondary.
Either the sparks went to the concrete floor, or they 
went to the ceiling. A few headed for
the bench saw around 30 inches away. The mounting 
tees had to be rotated 90 degrees so the arms would 
be parallel to the floor. The rods could then be rotated 
around the axis perpendicular to the long axis of the 
coil frame and  mounting studs so the gap could be 
increased. This is the position that placed a lot of 
torque on the mounting studs which
barely held the load. 

Using Terry's method for determing the coefficient of 
coupling (k), this coil couples
rather tightly at 0.194 for the 14.5 turns where the 
tuning seems optimum. Only an
occassional secondary to primary arc-over at the 
wider spacings of the rabbit ears.  The longest 
spark I  got from this coil was around 38 inches. 
I attribute this mostly to high corona losses.The 
toroids are obviously too small for the coil. The 
kinks in the aluminum tent poles produce corona, 
but most of the coronal loss was at the right-angle 
attachments to the mounting studs. Beautiful 
sparks shot out of the bottom end of the pvc tees 
and thru the access  hole for the screw. Clearly, the 
losses were too high for a longer spark. According 
to John Freau's spark length formula,
the coil with 2250 Watts input should be capable of 
an 80 - 90 inch spark. And finally,
the pedestal mount I designed is too unstable. 
The large secondary is supported only by
a 10 inch length of 3/4 OD Delrin tube. The mounting 
wobbled, and the secondary was always rotating 
around the single 3/8 inch bolt holding it to the tube. 

By this point I am  beginning to catch on that this 
beast is simply getting too large for the space 
available, and unless I lower the floor or raise the 
ceiling the end of this project
is coming into view. But I'm getting an education 
and I still want to get a spark longer than the 48 
inch length of the secondary.  Several things 
need to be tried to reduce the
coronal losses. It's back to the drawing board 
for a reengineered mounting,
new and larger toroids, and redesigned bunny ears.

End of part 1

Cheers,
Ralph Zekelman