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RE: [TCML] Re: Dummy load for optimum cap size Experimentation
Another idea is to mount an identical lamp near your test lamp (but not so
close as to attract primary sparks to it), and power it with variable
voltage DC (e.g. a variac into a bridge rectifier). Then adjust the variac
until the lamps are visually the same brightness. Then just measure the
power to the DC powered lamp. Probably you could do this using RMS AC power
measurements as well - e.g. with a kill-a-watt meter, since the comparison
lamp filament is nearly pure resistance at line frequency.
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Gary Lau
Sent: Sunday, August 08, 2010 12:22 PM
To: Tesla Coil Mailing List
Subject: [TCML] Re: Dummy load for optimum cap size Experimentation
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
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
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
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
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