Part II: Design Criteria: Problems And Solutions
2. High Voltage Design Problems
A subtle warning to the unwary.
A. Power Supplies: The Good, The Bad and the Ugly
i. The Ugly
A Tentative Neon Tranformer Based Full Wave Supply Schematic
Neon transformers are wonderful things. With built in magnetic overcurrent
shunts, they're nigh indestructible. But they're expensive. A 60 mA, 15
kV transformer costs about $200.00. Big HV diodes don't run cheap
either. Neither do big variacs. A 240V single phase one might
be had for $100.00 at a surplus store. Professionally built supplies
were used in this experiment.
ii. The Bad
HV supply manufacturers have traditonally used coaxial output wires
such as this "brand new" RGU-8 coax. This is NOT a bright idea!
Yes, I was stupid enough to play with this!
Until I shorted it out... right at 4kV...SURPRISE!
Hot rod SPARK PLUG WIRE! No problems since!
Its easy to connect and meant for VERY hostile environments. (Under your
hood.) The impedance is the same, 50 ohms/ft. It is also rated
for 60kV, which happens to be the supply voltage. (Ever been "bit"
when fooling with your own spark plug wires? That could easily have
been 35-60kV!) Why do they still use coax then? The
justification, that shielding against rf is required, is pretty weak.
Running a properly insulated conductor in a raceway with
a ground will shield very nicely. Better yet, ground the raceway.
There are other forms of HV wire besides ignition wire.
GTO-15, also known as "goat" or "neon" wire is an option. It was
used for a while on the 5kV Universal Voltronics supply that served for
several months. This supply left a bit to be desired. Rated
for "5kV", which was good enough for ascertaining confinement, it
invariably would blow a 50 ohm voltage divider load resistor as this
was the only overcurrent protection on the high voltage side of the supply!
This was annoying but the resistors were only $3.00. Finally, while
taking data, something a little more expensive blew on the primary side.
iii The Good
The Sorenson (Raytheon) Model 1061. (Rah rah Raytheon!)
Note the trip controls, protecting against both over-voltage and overcurrent.
The unit in the rack.
A separate filter.
The controller and filter, in the rack.