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

[nancylavoie@xxxxxxxxxxx]

While I'm not sure what the temp. rating of the kapton tape is, I do know that these lamps get pretty hot.I work with industrial heating systems for molding processes and we have very good luck with glass tape (3M makes a pretty decent one available at most suppliers like MSC or Grainger).Just a suggestion if you choose to go the tape route.Just a question though,are you using pre-made thermocouples or are you simply using thermocouple wire?The reason I ask is because I know that the off the shelf thermocouples often have provisions for fixing them to the heat source.You could simply fasten a bracket near the bulbs and using these connectors,run the ends of the thermocouples up against them. Wyatt
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-----Original Message-----
From: Gary Lau <glau1024@xxxxxxxxx>
Sender: tesla-bounces@xxxxxxxxxx
Date: Thu, 29 Jul 2010 10:14:36 
To: Tesla Coil Mailing List<tesla@xxxxxxxxxx>
Reply-To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
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


On Sun, Jul 25, 2010 at 7:40 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:

> I just thought of another use for the halogen lamp dummy load.  When one
> begins the design of a coil, after you decide what size NST you'll be using,
> the next step is to determine the tank capacitor size.  The standard method
> is to just look it up in a table for what size your NST is, using an LTR cap
> for a static gap, being some factor 1.3-1.7 times the mains-resonant value.
> Personally, I've found better results using ~2 times the mains-resonant
> value.
>
> Experimentally trying different cap sizes isn't practical, as each time you
> change the cap size, you must also change the secondary to keep things in
> tune (which changes multiple things, rather than just one), and you must
> also subjectively judge at what point the sparks are better, at widely
> distant points in time.
>
> However, if you replace the primary with the dummy load, one can quickly
> change the cap size and nothing else, and gauge the amount of power
> processed by the brightness of the lamps.  For a more quantitative result,
> you can mount a thermocouple on the lamp and see with what capacitor size
> causes the lamps to get the hottest.  I believe that this would give a very
> accurate determination of the optimum capacitor size.  I'll have to
> resurrect my coil and try this!
>
> I've also long suspected that the optimum cap size might differ
> significantly depending upon the applied AC voltage to the NST - potentially
> very different for 120 vs. 140VAC.  It would be easy to determine if this is
> true using a dummy load.
>
>
> Regards, Gary Lau
> MA, USA
>
>
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