# Measurements using field probe

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From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Sunday, June 28, 1998 7:42 PM
To:  Tesla List
Subject:  Re: Measurements using field probe

Terry, All -

very important to me and all the other coilers. The lamp meter is an
excellent method of measuring currents in an operating TC.  The TC RF
currents in the secondary are random pulses at high frequency. Ordinary
meters cannot accurately measure these currents. Even hot wire and
colometric meters have limited use because they are calibrated for only
special conditions.

Using a variety of lamps and suitable shunts and properly calibrated you
can measure TC currents for any condition. I made many of these tests
several years ago on some of my small coils as I show in my Tesla Coil
Construction Guide. Note that the lamp gives an RMS output instead of an
average output. Average is 63.7% of peak while RMS is 70.7% of peak. The
lamp output is non linear and limited but that can be taken care of by using
several different lamps  with appropiate shunts.

I not only measured the TC secondary currents but also was able to find
the overall efficiency of some of my coils. This is also shown in the Guide.
The efficiency was found to agree closely with the TC efficiency graph (Fig
7) I shown in the TC Notebook. As I have not found any coilers who have
duplicated the overall efficiency tests I have not been able to verify my
results. Hopefully more coilers like you will help me make verification
possible.

It is interesting to compare your estimate of 950 KV (at 100% eff) in the
secondary with the 462 KV in the JHCTES program. This gives a secondary
voltage efficiency of
(462/950) x 100 = 48.6 percent for sec cir, not overall.

The program shows 8.6 Inst peak amps in the secondary circuit. This gives
462 x 8.6/1000 = 3.97 Inst megawatts in the secondary.
I have not been able to verify your 31.62 amps. Could this current be
8.6/.486 = 17.69 amps??   and
sqrt(313) = 17.69?

For your toroid and coulomb calcs giving 47.43 uCoul.
The JHCTES program gives for   Q = C x V
(50^-12) x (462000) = 23.1 uCoul   and
(23.1 / 47.43) x 100 = 48.7 percent as above

The sec voltages, uCoul, and eff seem to work but not the sec currents.

Some experiments appear to agree with calcs but we have a long way to go.
We need more coilers to build, test, and do the calcs with more coils to
verify the above results. This can be done with small coils and does not
require big sparks!!

John Couture

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At 10:35 PM 6/27/98 -0500, you wrote:
>
>----------
>From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
>Sent:  Saturday, June 27, 1998 12:34 PM
>To:  Tesla List
>Subject:  Re: Measurements using field probe
>
>Hi Bert and All,
>
>	Since this has become a public post I will answer it here.  There is a lot
>of good science in this many will be interested in.  My comments are at the
>end regarding the light bulb test.
>
>At 10:22 PM 6/26/98 -0500, you wrote:
>>
>>----------
>>From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
>>Sent:  Wednesday, June 24, 1998 10:17 PM
>>To:  Tesla List
>>Subject:  Re: Measurements using field probe
>>
>>Tesla List wrote:
>BIG SNIP>>>>>>>>>>>>>>>>>>
>>-- Bert --
>>=======================================================================
>>Test #2:
>>========
>>Subject: Light Bulb Experiment (Followup)
>>   Date: Fri, 27 Sep 1996 23:24:14 -0700
>>   From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>>     To: tesla-at-pupman-dot-com
>>References: 1
>>
>>Here's a "Light Bulb Experiment" and toroid-ground discharge update:
>>
>>Previously, I had used various sizes and wattages of light bulbs placed
>>in series with the corona current path. These lights unexpectedly
>>"dimmed" when passing heavier toroid-ground discharge currents. Dave
>>Huffman and Robert Stephens theorized that these higher current
>>discharges were bypassing the filament path due to unseen arc-overs
>>between the lamp-base leads. And after a few more experiments, I
>>concurred, but had no direct proof.
>>
>>I just tried a slightly different experiment using a 100 Watt tungsten
>>halogen lightbulb. This bulb is about 2" long x 1/4" diameter, with the
>>filament going the length of the bulb, and having a ceramic & metal
>>termination at each end. This particular construction prevents any
>>flashovers, forcing both the corona and ground surge currents to flow
>>through the filament. Because of the larger filament wattage, I was only
>>just barely able to light the bulb when running streamers to air through
>>the filament. However, once toroid-ground discharges began between the
>>free end of the lamp and a grounded wire 42" above, the filament began
>>to glow fairly brightly.
>>
>>This helped confirm that the previously observed dimming associated with
>>Mazda-based lamps was indeed an artifact due to the heavy current arcing
>>around and bypassing the filament. I very carefully observed the average
>>brightness of the bulb under the heavy-discharge condition while running
>>the coil at maximum power. I then connected the same bulb to a variac
>>and an AC ammeter to estimate the average current necessary to light the
>>bulb to an equivalent degree. This level was reached at about 400 MA,
>>implying that the lamp was seeing an "average" current level of about
>>400 MA during the ground discharges (sort of like a hot-wire
>>ammeter...).
>>
>>Further measurements with a storage scope showed that each
>>toroid-to-ground discharge removed virtually ALL of the energy in the
>>Primary/Secondary system in a very short time. There was no further
>>ringdown, or any other activity until the next "bang". Each discharge
>>occurred near the first peak of secondary voltage (i.e., during the
>>first energy transfer/"Bang"). Each high-current discharge actually
>>consisted of an exponentially damped 10-20 MHz current, with virtually
>>all of the energy being dissipated in about 1.5 uSec. At full power, the
>>primary gaps fire 3 to 4 times every half cycle, or between 360 and 480
>>PPS. For analysis purposes, an average rate of 420 PPS will be used.
>>
>>Using 420 PPS, with each toroid-ground current surge lasting only 1.5
>>uSec, the total time "ON" time per second is about 420 x 1.5 uSec or 630
>>uSec, implying a duty cycle of only about 0.063%. The toroid-ground
>>current peaks which would have to flow to "average" 400 MA can now be
>>estimated: Isurge=(0.400)/(630x1e-6) or about 635 Amps(!). However,
>>since the actual current surges are exponentially decaying during each
>>1.5 uSec shot, the actual current peaks are probably significantly
>>greater than 1000 Amps(!).
>>
>>This explains why these discharges look so mean and evil... they ARE!
>>As always, flames, brickbats, and snickering are always welcomed.  <:?)
>>
>>Safe (and rubber-booted) coilin' to ya!
>>
>>-- Bert --
>>=======================================================================
>
>
>
>
>I believe the 1000 amp spike level is far too high.
>
>A 144 ohm filament (100 Watts 120 Volt) with 1000 amps going through it for
>1.5 uS will dissipate I^2Rt joules.  That works out to 216 joules per arc.
>At 420 BPS we would dissipate 97720 watts in the bulb!!
>
>Also, the top toroid is a capacitor.  The charge on a capacitor is equal to
>the capacitance multiplied by the voltage (Q = C x V).  The charge is also
>equal to the current multiplied by the time. (Q = I x t).  For 1000 amp and
>1.5 uS the charge would be 1500 uCoul.  For a toroid of say 50pF the voltage
>works out to 30 million volts!!  That's too high!  But a good try :-))
>
>The problem was introduced when you assumed the following:
>
>"I then connected the same bulb to a variac
>and an AC ammeter to estimate the average current necessary to light the
>bulb to an equivalent degree. This level was reached at about 400 MA,
>implying that the lamp was seeing an "average" current level of about
>400 MA"
>
>Actually the power was equivalent not the current.  The power is
>proportional but current is a squared function.  This threw everything off
>by a squared function.
>
>If we go back and redo the previous calculations with the square root of
>current ( SQRT(1000) = 31.67 ) we get the following.
>
>A 144 ohm filament with 31.62 amps going through it for 1.5 uS will
>dissipate I^2Rt joules.  That works out to 0.216 joules per arc.  At 420 BPS
>we would dissipate 90.72 watts in the bulb - Much more believable!
>
>Also, the top toroid is a capacitor.  The charge on a capacitor is equal to
>the capacitance multiplied by the voltage (Q = C x V).  The charge is also
>equal to the current multiplied by the time. (Q = I x t).  For 31.62 amp and
>1.5 uS the charge would be 47.43 uCoul.  For a toroid of say 50pF the
>voltage works out to 950 kilovolts - A much better number.
>
>Also the top terminal capacitance and the arc form a RC network that should
>discharge in 5 RC time constants.  This would imply a resistance of:
>
>1.5 uS = 5 x R x C
>
>With say a 50 pF top terminal the resistance implied is 6000 ohms!  This is
>comparable to the values I see of ~2000 ohms for arc current!  I think we
>are getting some interesting correlation here!!
>
>Note that 950 kV / 6000 ohms gives a current of  158 amps.   Higher than
>31.67 and lower than 1000.  The linear decrement and the guesses I have made
>have introduced some error.  However, I believe the principles are sound.
>We are at least in the hundreds of percent.  Usually this stuff has been
>many orders of magnitude off in the past!!!  We are getting much better!!
>
>To make a long story short... just remember that the light bulb illuminates
>in proportion to the current squared and all should work out reasonably well.
>
>
>The fact that we independently are getting resistance values for arcs to
>ground in the 1 to 10 kiloohm range is very significant!  I should point out
>that without the antenna being properly terminated, the antenna and cable
>will ring from the impulse of an arc.  This false ring may make the
>decrement look about 250% longer than it really is.  If this affected your
>measurements, the real numbers would work out very accurately to what I
>would think is really going on.  My plane wave antennas had this problem in
>the beginning.  Thus, all the coax-matching resistors were added to it.
>
>Thanks for sharing this neat experiment.  Hopefully it can now be well
>understood what it was showing.  It is wonderful that we are know seeing the
>first bits of good data coming in regarding output arcs.  Once such things
>are understood, we can make design changes to really push the arcs.  I am
>intrigued by a scope graph I have taped to my computer that shows the burst
>during an arc producing 3.5 times the original secondary voltage.  If this
>effect can be understood and optimized...........
>
>
>All the best
>
>	Terry Fritz
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