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Re: Light Bulb Experiment (Followup)



>From bert.hickman-at-aquila-dot-comSat Sep 28 10:13:58 1996
>Date: Fri, 27 Sep 1996 23:24:14 -0700
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Light Bulb Experiment (Followup)

>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 --

Bert,

That's one fine job of conjecture and analysis.  I buy it!  Did you 
ever think of becoming an engineer?  Take the rest of the day off, 
with pay!.

The numbers you come up using the long tungsten bulb are certainly 
believable.  You only failed to multiply the 1000 amp peak output 
current available in the secondary 'pop' by the output voltage into the 
streamer which may be several hundred kilovolts.  That sounds like a 
peak power of several hundred mega-watts for maybe a portion of that 
1.5 microseconds.  It would be useful to be able to measure the actual 
time duration of the single discharge streamer optically just like they do with 
real lightning flashes.  I'm not at any diagnosis/analysis level yet with my 
testing for lack of shop space (soon to be remedied), but I guess 
with a pickup antenna an o-scope should be able to tell us what we 
need to know here.  I wouldn't mind placing a battery powered scope 
in a faraday cage and sit it on top of the toroid with an RF current 
probe around a piece of wire sticking out of the toroid sideways that 
will create a streamer.  This way with a telescopic optical viewing 
device we could observe the current waveform being launched from the 
capacitance of the topload into a streamer to air and also into an 
arc to a ground target.  

Something I may do some time for a lab coil is wind the secondary 
with two separate insulated wires (bifilar) so you can run 120 vac to 
operate test equipment on top of the secondary at megavolt elevation.
This would work for the test I just suggested if you didn't have access to a
battery powered oscilloscope.  But then again I guess you could also just put 
a 12 volt gel-cel battery and power inverter topside.  I hope Brent 
is tuned into this.  Brent, wind a bifilar secondary, man.  You could sit up there
with a coffee pot going! :-).

Regards,

rwstephens