Re: Static gap BPS, was Static Spark Gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

At 07:01 PM 4/24/2003 -0400, Matt D. wrote:
>In a message dated 4/24/03 4:30:05 PM Eastern Daylight Time, 
>tesla-at-pupman-dot-com writes:
>
>
>>This seems consistent with my memory that at 2*Res (17.84-nF) I get a
>>very very distinct 60-Hz machine-gun-fire sounding result from my static
>>gap TC. I've always disliked that sound and avoided it, but it also seems
>>to give nice long streamers. This seems consistent with the notion that
>>the primary capacitor is consistently charging up with two full half
>>cycles for a large bang size.
>
>
>Hi Terry, All,
>
>This is very hard for me to envision. Seems like at 2* res, the cap would 
>charge to V/2 on the first quarter cycle then discharge to zero on the 
>second quarter cycle and then, because of the reversed polarity, charge to 
>V/2 in the reverse direction, etc., giving zero BPS. It also seems that if 
>the bps is not a multiple of the supply frequency, you may get, say, 200 
>BPS, but they will not be uniformly spaced or of uniform duration. Am I 
>missing something?
>
>Matt D.


If the voltage is at say -v, then the current is doubled, so the charging 
rate is doubled.  At 200 BPS, the rate varies over a small 1/60 second time 
span.  The 200 BPS is an 'average' over many cycles.  I think the data in 
my charts is over 1 second.

>Terry,
>       according to your NSTStudy tables, using my 9-30 NST, and taking into
>account your point about Watts I get:
>
>         8.8-nF (res)    200 BPS, 143 W  ->   .7 J/bang
>         12-nF           120 BPS, 117 W  ->   .975 J/bang
>         18-nF           60 BPS,  88 W  ->  1.47 J/bang
>
>(I think I'm doing the math right, Watts / BPS -> J/bang ?)
>
>I expect the 200 BPS to be variable in bang size since its semi-chaotic
>so spark length may be hard to predict, but the 120 and 60 BPS should (?)
>be fairly synchronous and hence stable and predictable...
>
>If we can extrapolate J.Freau's formula, 60bps should give 22% longer spark
>than 120bps in this setup (sqrt(1.47/0.975) = 1.22).
>
>I built an MMC with four strings selectable in parallel, each with 4.8-nF,
>so I can try  4.8,  9.6,  14.4, and 19.2 nF. My strings should be a wee bit
>longer to get the capacitance down to 8.8, 12, and 18 nF, but the enclosure
>has already been built, next time...
>
>
>-Pete Lawrence.

Try the "real" test and see...  These computer modeling things may easily 
goof, so we need that 'real' data to be sure they are on track.  I always 
hate to blindly trust computer predictions until we can directly overlay 
real data and say "See, they are the same!" ;-))


>Terry,
>       I guess it would be interesting to add three more columns to your
>NSTStudy tables. The first would be average Joules-per-Bang, the second
>would be maximum Joules-per-Bang, and the third would be frequency of the
>maximum bangs. The first is easy (RealPrimaryCapPower divided by BPS), the
>second and third would require looking at the output of the circuit
>simulation over time to see how the bang size was varying...
>
>-Pete Lawrence.

The original data took like two days of computer crunching ;-)  But I think 
far more data was available in the original Excel file.  I tried real hard 
not to miss anything.

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTtest.xls

As I look over that file, I don't see too much additional info 
though...  Computers are faster now and the original models did show 
everything in excruciating detail...  The models and programs are all there 
if you want to repeat anything.

Cheers,

         Terry