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

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

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
> 
> 
> 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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