"The
MiniKatz Coil"
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Introduction
Now that I have successfully built a sweet four inch tesla coil, I decided to build something a little smaller that
could be transported easily and even kept on my desk at work for a working tesla coil display. At a recent tesla
event, I got the chance to see Gary Lau's tabletop tesla coil (see http://www.laushaus.com/tesla/minicoil.htm) and
decided to use his design as a starting point for my "MiniKatz Coil", so named in keeping the convention of the
many lighting products I've designed at Space Cat Advanced Lighting Systems.
As of now, all components are already acquired, and I am challenging myself to build, test, and finish this unit within
two weeks! Keep watching this website as more pictures will be added daily.
Future Improvements
My coils first entry into Gary Lau's tabletop tesla coil showdown was relatively weak compared to the other
entries. (see http://www.laushaus.com/tesla/minicoilcontest/index.htm ) My longest continous streamer
length is approximately 9 inches. The following future modifications should however theoretically increase
my streamer length by 2 or 3 more inches.
- Increase spark gap distance to approximately 0.050-0.060 inches. Currently the gap is set at 0.040 inches.
This will allow the voltage to build up a bit more on the primary capacitor and force more energy into
the primary coil when the spark gap conducts.
- Increase the value of the primary capacitor from about 0.0122uF to 0.0244uF. This higher value it closer to the
proper resonant size capacitor for a 4kV, 38mA NST which optimally should be 0.0252uF. Completed 4/2003
- Use a larger toroid. Currently, the break-out voltage of the toroid is a bit low resulting in a high number of
short to mid-size streamers. A large toroid would require a higher voltage to be built up before a streamer
breaks out. Theoretically, this would result in a reduced amount of streamers, but longer in length. Completed 4/2003
The above changes are very easy to implement, however the difficult (or rather tedious) part is the re-tuning of
the primary tank circuit due to the changed capacitor size and changed toroid size.
Performance Update
I recently made some modifications to this "MiniKatz" coil to increase performance. As listed above, I've increased my primary
tank capacitor from 0.0122uF to 0.0244uF and also built a larger toroid for the unit. After retuning the coil, I managed to
get about 12 inches maximum spark output which is a 33% improvement in spark length over the initial configuration of the
"MiniKatz" coil.
During a recent tesla event in Rochester, NY, a new arc length was set by the "MiniKatz" coil. New maximum arc length is about
12.5 inches which was measured officially by myself and Gary Laus.
I've recently increase toroid size using two 2x8" toroids stacked. Performance now exceeds 15 inches to a strike plate.
(December 2003)
System Schematics
The following schematic is the final design for the "MiniKatz" tesla coil. (Requires Adobe Acrobat 5.0)
HV Power Supply
4kV, 20mA Franceformer Open Frame Neon Sign Transformer (NST)
Part No. 4020SE
Price $25.00 NEW
For this coil, I will remove 50% of the shunts and have a modified NST running 4kV at 38mA (as measured by
Gary Lau)
Protection Circuitry
The only protection circuitry which will be used in this design is a simple safety gap formed by two stand-offs with
adjustable 0.5" corona balls. Note: This safety gap is currently not used on this tesla coil.
Primary Tank Capacitor (MMC)
The primary tank capacitor will be comprised of five (5) 0.056uF, 1500V polypropylene capacitors in series creating a
0.0112uF, 7.5kV MMC.
Spark Gap
The spark gap will be a simple static gap consisting of two (2) 1.125" diameter x 3.00" long copper pipers spaced at 0.050".
There is a possibility I will use a fan in my design to add airflow to improve performance of the static gap.
Primary Coil
The primary coil will be a flat-pancake type coil spaced approximately 0.5" from secondary using 1/8" copper
refrigeration tubing.
Secondary Coil
2" PVC coil form (2.375" O.D.)
30 AWG
Winding length: 12"
H/D Aspect Ratio: 5.05
Toroid
I will be using a 1.625" x 6" spun aluminum toroid which was made by John Freau. Total capacitance is approximately
6.66pF. You can obtain one of these small toroids by ordering from John Freau here.
Enclosure
The unit will be built inside a structure consisting of two (2) 10" x 10" x 1/4" clear polycarbonate sheets with four (4) 3/4" diameter
extruded acrylic rods for supports.
Coil in Action
The following pictures show the "MiniKatz" coil in action. So far, maximum streamer length is about 9 inches.
Here's a good comparison shot of the "MiniKatz" coil and my new ten inch secondary coil !
Lessons Learned
1. Acrylic is absolutely horrendous when it comes to machining it. Avoid it at all costs!!!! I even had difficulties trying to tap
some holes in polycarbonate. Therefore, I have moved to good ole 6061 aluminum for my supports.
More to come soon . . .
Logo, photos and original text are Copyright © 2003 by Eastern Voltage Research Corp.
All Rights Reserved. © 2003 Christopher Hill Web Master.
Last modified August 16, 2005 08:05:20 PM