[TCML] Re: Dummy load for optimum cap size Experimentation

[Gary Lau <glau1024@xxxxxxxxx>]

Here's a status update on my experiment to determine the best capacitor
value to use with a static gap, by monitoring the light intensity generated
by a halogen lamp dummy load in place of the primary coil.

I've abandoned attempting to monitor the lamp temperature.

I've replaced CdS and Selenium plotocells with a photodiode.  This appears
to be more stable with temperature.

It's necessary to filter the photosensor output to smooth out the variations
that occur due to the chaotic firing of the static gap.  Originally I just
used a very slow (~20 sec) R-C low pass filter, feeding a voltmeter, but I
still saw variations - the output never reached a stable equilibrium.
Here's what the unaveraged light intensity looks like over a period of 2
minutes:  http://drop.io/garylau

I'm now reading the photodiode into an A/D converter and processing that
with a LabVIEW program.  I sample every 10 msec and calculate a moving
average over 60 seconds.  But even over that interval, I still see
variations over time and from run to run.  If I look for a peak value on the
60-second moving average, I will see new high values occurring many minutes
into the run, less and less frequently with time, but it's impossible to
come to a final definitive value.

I found that sanding the sucker gap contacts made a HUGE difference in light
output, so I'll have to sand them briefly for each data point (yes I'm
careful not to disturb the gap width).

It looks like I'm going to have to live with the fact that static gap
systems cannot deliver a stable and repeatable amount of power, and hope
that the differences in power throughput with different cap values will be
significantly greater than averaged gap power fluctuations.  Stay tuned for
more.

Regards, Gary Lau
MA, USA



On Sun, Aug 8, 2010 at 2:21 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:

> OK, back from vacation, time to start the experiments!  Igor???
>
> I tried monitoring the lamp brightness using a photocell.  Previously I
> just applied Variac'ed AC to the bulbs to test the photocell response.
> Today I hooked up the actual spark gap and capacitor to an NST.  Just as I
> feared, the chaotic gap behavior resulted in extremely erratic resistance
> readings.  Useless.  I tried placing a big cap across the photocell
> terminals, but that didn't work.  Back to monitoring the bulb temperature
> with a thermocouple.
>
> Previously I was using a fairly heavy-gauge thermocouple, something like 20
> gauge.  I think this may have contributed to the long time needed to reach
> thermal equilibrium.  I found another thermocouple made of very fine wire,
> and I used a couple turns of thin copper wire to strap the junction to the
> bulb.
>
> The thermocouple went to a battery-powered Fluke model 52 digital K/J
> Thermometer, same size as most Fluke DMM's.  But as soon as the gap started
> firing, the meter display went nuts.  The thermocouple wire is as far from
> the lamp wires as possible, definitely not making electrical contact, but
> inherently close.  The display returned to correct operation after cycling
> power, but the temperature was already in decline.  I tried looping the
> slack thermocouple wire 6 times through a big ferrite toroid, hoping to
> reduce the interference, but no luck.  Maybe a grounded metal sheath on the
> thermocouple?
>
> I also tried reading the thermocouple directly into a DMM on the 200mV
> scale.  Yes this lacks cold junction compensation, but could be useful just
> for relative readings.  But the readings were similarly flakey as long as
> the gap was firing, though at least didn't send the meter into a
> weird-mode.
>
> I also tried an analog wattmeter.  Someone suggested using a Kill-a-watt
> meter to just monitor real power consumed.  But even the analog meter shows
> wide fluctuations with the gap's chaotic firing - not useful for any but the
> most coarse reading.
>
> I'm stuck.  Any ideas, either for filtering, or an alternate readout
> device?  I'm starting to think about finding an analog pyrometer meter on
> eBay, but I was really hoping for digital resolution.  Dang - what seemed
> like such a simple method is turning into real project!
>
>
>
> Regards, Gary Lau
> MA, USA
>
> On Thu, Jul 29, 2010 at 9:36 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>
>> Time to eat some words.
>>
>> I tried various amateurish ways to couple the thermocouple to the halogen
>> lamp.  The kapton tape made a drippy stinky mess as soon as the bulb got
>> maybe 30% power.  I tried pressing the thermocouple to the bulb with a
>> spring, and put a layer of fiberglass drapery between the spring and
>> thermocouple.  The drapery pigments smoked and made a mess.  Perhaps some
>> better quality fiberglass may have worked better, but when I was using the
>> kapton tape, the time to reach equilibrium seemed excessive - several
>> minutes, and given that I'll be taking data on MANY data points, I'm just
>> not that patient.  So I'll be using a photocell and Ohmmeter.  Maybe I can
>> just throw a cap across it if there are fluctuations.  At the power levels
>> (~50%) I was trying just now with simple line AC, the brilliance of the
>> halogen lamp swamped any room illumination, so shielding probably is not an
>> issue.
>>
>> On Thu, Jul 29, 2010 at 10:14 AM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>>
>>> I'm gathering materials and plans to perform this experiment -
>>> determining the cap size that will extract maximum power from an NST, at 120
>>> and 140VAC input.  The power indication will be via monitoring the surface
>>> temperature of the halogen lamp dummy load that replaces the primary coil.
>>> I plan to test a 15/60 NST, and two 15/30 NST's, all unmodified.
>>>
>>> <snip>
>>
>>
>
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