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

Hi Gary,
The thermocouple might work assuming it's a surface temp type. I would simply place a metal sheet over the lamp(s) and mount to that (it's all relative regardless). However, I've done the lamp method before and it wasn't that difficult and the readings were quite smooth and gentle.
I put two 500W halogen lamps inside an aluminum box totally enclosed. I then drilled a 3/8" hole in the side of the box where I mounted a light to voltage transducer. Prior to mounting the transducer, I used black electrical tape all over the transducer except for a small 1/4" area which was aligned over the hole. Ran small coil and measured the voltage across the transducer (grabbed a few samples and averaged). Later I used a variable DC supply measuring voltage and current to achieve the same light level needed for the transducer voltage average. Pretty simple method and worked quite well to gather a real power number. 

Regards,
Bart B. Anderson

Gary Lau wrote:

I don't have an IR thermometer but I do have a digital thermocouple meter,
so...

Two possible problems with measuring the light.  I'd have to build a
ventilated, shielded enclosure to keep out ambient light, and that seems
like more effort than finding a way to couple the thermocouple to the lamp.


Additionally, I fear the thermal time constant of just the filament would be
faster than the long-term fluctuations in the chaotic gap firing rate, and
would show moment-to-moment variations in brightness.  I'm hoping that the
thermal time constant of the quartz tube and thermocouple will average out
such variations and yield a more consistent reading.

I'll try the kapton tape and see how that holds up.

Regards, Gary Lau
MA, USA


On Thu, Jul 29, 2010 at 5:18 PM, Yurtle Turtle <yurtle_t@xxxxxxxxx> wrote:


Wouldn't it have to run a while to get up to temperature? Why not measure
light
intensity?



----- Original Message ----
From: Binny <binny@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thu, July 29, 2010 8:00:55 PM
Subject: Re: [TCML] Dummy load for optimum cap size Experimentation

HI,
    Wonder why one wouldn't use one of those non contact IR Thermometers?
They're relatively inexpensive and fairly accurate.
----- Original Message ----- From: "Gary Lau" <glau1024@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, July 29, 2010 7:14 AM
Subject: [TCML] Dummy load for optimum cap size Experimentation



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.

I'm having a hard time figuring out how to fasten a thermocouple to the
quartz lamp tube.  I want the connection to be robust, as there will be
considerable thrash as I change NST's and cap sizes, and I don't want
lamp/thermocouple coupling to vary.

Obviously I'll clamp down the thermocouple wire to the base of the lamp
assembly (http://drop.io/garylau), but could use guidance on the

business

end.  I thought about just wrapping many turns of 30 gauge copper wire
around the thermocouple wire and quartz tube, but worry that the quartz

and

copper will have differing expansion rates and might damage the tube.  I
have high-temperature polyamide (kapton) tape that I can wrap the
thermocouple to the tube - not sure how that will fare with the heat.  If
nothing easy presents itself, I guess I'll fashion a spring clamp to

apply

gentle pressure to the thermocouple tip and tube.

Any thought on this problem or the experiment design would be welcome.

Also, I can't seem to locate the table that relates NST size and gap type

to

suggested cap size.  It had been on hot-streamer and mirror sites, but I
can't seem to locate it.

Regards, Gary Lau
MA, USA

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