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

[mddeming@xxxxxxx]

Hi Gary,

If you are looking for relative rather than absolute values, perhaps a remote-reading IR thermometer in a fixed bracket pointed at a fixed target on the bulb assembly and read at both the start and the same number of seconds into each run, would give a quick and cheap way of measuring relative energy output.

Matt D.






-----Original Message-----
From: Gary Lau <glau1024@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thu, Jul 29, 2010 10:14 am
Subject: [TCML] Dummy load for optimum cap size Experimentation


I'm gathering materials and plans to perform this experiment - determining
he cap size that will extract maximum power from an NST, at 120 and 140VAC
nput.  The power indication will be via monitoring the surface temperature
f the halogen lamp dummy load that replaces the primary coil.  I plan to
est 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
uartz lamp tube.  I want the connection to be robust, as there will be
onsiderable thrash as I change NST's and cap sizes, and I don't want
amp/thermocouple coupling to vary.
Obviously I'll clamp down the thermocouple wire to the base of the lamp
ssembly (http://drop.io/garylau), but could use guidance on the business
nd.  I thought about just wrapping many turns of 30 gauge copper wire
round the thermocouple wire and quartz tube, but worry that the quartz and
opper will have differing expansion rates and might damage the tube.   I
ave high-temperature polyamide (kapton) tape that I can wrap the
hermocouple to the tube - not sure how that will fare with the heat.  If
othing easy presents itself, I guess I'll fashion a spring clamp to apply
entle 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
uggested cap size.  It had been on hot-streamer and mirror sites, but I
an't seem to locate it.
Regards, Gary Lau
A, USA

n 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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