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neon data-reformated
---------- Forwarded message ----------
Date: Sat, 18 Oct 1997 15:16:00 -0500 (EST)
From: Benson_Barry%PAX5-at-mr.nawcad.navy.mil
To: tesla-at-pupman-dot-com
Subject: neon data-reformated
Hi All,
Since so many people have been asking about
protecting neon sign transformers, I thought it might be
useful to repost this series of measurements that I made
last year in reformatted and hopefully readable form.
Barry
"I made a few measurements on a Jefferson 15,000 volt,
60 mA neon sign transformer:
Secondary resistance of terminal
1(near ground lug): 3.375 Megohm
Secondary resistance of terminal
2(near 120V terminals): 4.2 Megohm
Inductance: meter went beserk. Couldn't get a
reading!
For the next measurement I connected two different
capacitors between
the signal generator and terminal 2 (used for all
measurements). The other
lead of the signal generator was grounded to the
transformer case. An
oscilloscope was connected between terminal 2 and
the transformer case.
---------------C----------------Fr
-------------0.1uF-------------30Hz
------------0.01uF------------105Hz
Then I used Howe's method (page 453 of Radiotron
Designers Handbook 4'th edition) plotting C VS
1/Fsquared to find the self capacitance using
the x intercept formula x = (x1y2 - x2y1)/(y2 - y1)
where
y2 = 1/(30 squared) = .00111
x2 = .1uF
y1 = 1/(105 squared) = .000090702
x1 = .01uF
x = ((.01uF X 0.00111) - (.1uF X 0.000090702))
/ (0.00111 - 0.000090702)
= 2.002 nanoFarads
Then I performed the following calculations using
the simplified formula for inductance (the high
resistance tends to make this slightly inaccurate):
L = 1/(2 X PI X frequency X capacitance) where
capacitance = Cself of coil + C(required to resonate)
--------------Fr-------------------L
------------105Hz----------------191.4 Henrys
-------------30Hz----------------275.92 Henrys
The next set of measurements were performed to
ascertain the effect of various inductors, capacitors,
and resistors hung off the high voltage terminal of
the transformer. Terminal 2 was used. The setup
consisted of the following: A 200,000 Volt diode was
connected from the high voltage lead of the
transformer to a 3 Megohm resistor which was connected
to one terminal of a 0.1 uF, 25 kV capacitor. The
other terminal of the capacitor was connected to
ground. A dump switch was connected between the hot
end of the capacitor and ground for safety. The hot
end of this capacitor was also connected to a high
voltage voltmeter with an input impedance of 1 Gigohm
(Collmer Semiconductor, Inc, "Digital H.V. meter"
Model # CS5190A1) to act as a peak reading DC
voltmeter. All high voltage DC measurements (HVDC)
were made this way. AC measurements (HVAC) were made
with a Hipotronics high voltage probe (Model #:
KVM-200D, part #: 45-125 (used the stack only)) with
a maximum frequency of 1Khz, an impedance of 750
Megohm, and a ratio of 2000 to 1. The Hipotronics
probe was connected to an oscilloscope. The ground
side of the probe was connected to the grounded case
of the transformer. Measurements from the scope
(1 Megohm, AC coupling) were made with automatic
cursor lines with direct digital readout.
For the first measurement I connected the
Hipotronics probe directly to the high voltage
terminal 2 of the transformer to measure the
transformer voltage without anything else attached
to it:
input VAC-----HVDC output-----HVAC output
----118---------10.7 kV-------9.75 kV P-P
scope waveform description
----60 Hz sine wave
For the next set of measurements I connected various
doorknob capacitors and a 300mH torroidal inductor
(1" id X 2" od X 1/2 " thick + 40 turns of #16
magnet wire) directly from the high voltage terminal
2 to ground. Where the inductor was used it was
connected between the terminal 2 and the capacitor.
Lower voltages were used to protect the transformer
(except in one instance).
neon
trans..
input-----HVDC-------HVAC------connected-to-terminal
-VAC-----output-----output---------C-----------L
volts------Kv---------kV-----------pF----------mH
112.7----10.7-------10.18---------500---------none
----------
----------Scope waveform description:
----------60 Hz sine wave almost triangular
----------with a shoulder near the peak.
----------
-------------------------------------------------------
112.9----10.7-------10.18---------500---------300
----------
----------Scope waveform description:
----------Same as above.
----------
-------------------------------------------------------
112.2----10.7-------10.18---------500---------300
----------
----------Scope waveform description:
----------Same as above with probe connected
----------to where the inductor and capacitor
----------connect together. Inductor appears
----------to make no difference.
----------
-------------------------------------------------------
112.7----12.7--------12.7---------1000--------none
----------
----------Scope waveform description:
----------Brought voltage up and then down
----------too quickly to get a scope reading.
----------Didn't want to cook transformer.
----------(Wicked buzzing sound inside the transformer.)
----------
--------------------------------------------------------
100.7----10.7--------10.7---------1000--------none
----------
----------Scope waveform description:
----------60 Hz triangle waveform with
----------buzzing sound from transformer.
----------
--------------------------------------------------------
100.5----10.7--------10.7---------1000---------300
----------
----------Scope waveform description:
----------Same as above.
----------
--------------------------------------------------------
100.7----10.7--------10.7---------1000---------300
----------
----------Scope waveform description:
----------Same as above with probe connected to where
----------the inductor and capacitor connect together.
----------No difference from inductor.-
----------
--------------------------------------------------------
86.9----10.7---------9.68---------2000---------none
----------
----------Scope waveform description:
----------Distorted squarish sine wave with shoulders
----------at 6.375 kV on one side.
----------
--------------------------------------------------------
105.2----10.7--------9.44---------3000---------none
----------
----------Scope waveform description:
----------Same as above with a more square wave
----------like appearance with shoulders at 7.125 kV
----------on one side.
----------
--------------------------------------------------------
109.3----10.7--------9.31---------4000---------none
----------
----------Scope waveform description:
----------Same as above with a very square wave
----------like appearance with shoulders at 8 kV
----------on one side.
----------
--------------------------------------------------------
109.3----10.7--------10.7---------4000---------300
----------
----------Scope waveform description:
----------Same as above.
----------No difference from inductor.-
----------
--------------------------------------------------------
For the next measurements I tried clamping the voltage
with varisters (GE part number-7226-19):
--------------------------------------------------------
118.4-----9.3---------9.3---------1000---------none
----------
----------Scope waveform description:
----------Same as above with a very square wave
----------like appearance with notched spike like
----------shoulders. Used a stack of 10 (800 V)
----------varisters in series connected to HV output
----------terminal 2. They got very hot to the touch.
----------
--------------------------------------------------------
101.9-----10.7--------10.7--------1000--------none
----------
----------Scope waveform description:
----------60 Hz triangle wave. Connected a stack of 12
----------(800V) varisters in series across HV output
----------terminal 2. They got slightly warm to touch.
----------Conclusion: Need some really big varisters for
----------effective clamping action!
----------
--------------------------------------------------------
For the next set of measurements I tried various
resistors in series with the HV terminal 2.
The resistances were made up of combinations
of 2 watt carbon composition resistors to
keep down the voltage stress:
--------------------------------------------------------
87.6------10.7--------9.75--------2000--------none
----------
----------Scope waveform description:
----------Triangle wave with shoulders at 3.437 V P-P.
----------1 k ohm resistor.
----------
--------------------------------------------------------
87.6------10.7--------10.7--------2000--------none
----------
----------Scope waveform description:
----------Same as above but with HVAC probe connected
----------at junction of resistor and capacitor.
----------1 k ohm resistor.
----------
--------------------------------------------------------
87.6------10.7--------9.75--------2000--------none
----------
----------Scope waveform description:
----------Triangle wave with shoulders at 3.437 V P-P.
----------5 k ohm resistor.
----------
--------------------------------------------------------
98.0------10.7--------9.56--------2000--------none
----------
----------Scope waveform description:
----------Triangular sine wave.
----------10 k ohm resistor.
----------
--------------------------------------------------------
These measurements seem to indicate that the only way
to protect the neon sign transformers high voltage
output from itself would be to put a series of
humongous varisters and or safety gap across it.
A 5 kohm resistor with RF inductor + 500pF bypass
capacitor + another RF inductor (to keep the bypass
capacitor out of the tank circuit) might be a good
combination to keep the RF out of the transformer.
Will try to measure this combination when I
complete my small measurable (portable) Tesla coil.
All of these measurements were made with only ONE
UNLOADED HV terminal to see what the voltage
might become if the spark gap on the Tesla coil
primary were opened too wide."