Re: NST's shorting out.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: MARTINFRYML@xxxxxxx

These are follow up questions are for Terry regarding your email:

If you doubled the number of NSTs without
changing the primary capacitor size, it is very
possible that the primary will go resonant and
over voltage the NSTs.  12kV at 120mA has a
resonant capacitor size of  27.3nF.  If you are
running 30nF (from below), then you are right on
top of the resonant value.  If nothing stops it,
the voltage might skyrocket to say 80kV!!!

Two follow up questions here.  Is there a 
difference in the resonant cap size between 
running a "modified" single NST (removing some 
shunts and running only 15-20 sec to prevent 
overheating) at 120 ma versus running 2 NST's in 
parallel where you have two cores 
operating?  Does the Java program take this into account?

Second, what if I run at 180 ma ?
The primary resonant capacitor size would now 
be   0.0398 and my smaller .03 cap would be 
considerably below that value.    Would this be 
less likely to cause the resonance voltage spikes?


A rotary gap that is not a synchronous type is
not recommended at all.  It will randomly fire at
any spot on the AC cycle.  A sync gap is twice as effiecient:


Besides the efficiency difference, is there any 
other reason to get rid of the async gap?  Do you 
think it is contributing to the kickback?

It was a significant improvement to my static gap 
( SG wasn't air quenched, though) so I really 
hate to get rid of it just yet.  A synchronous 
gap is not on the horizon right now.


As far as another approach to eliminating the 
primary resonance, what if I add an extra turn to 
the primary coil?  Then the system becomes 
detuned even further, with the reference cap size 
going down from .026 to .021.  Would this make 
the system less prone to these resonant spikes?  (Java run below):

Primary Outputs:
96.81 kHz = Primary Resonant Frequency
15.87 % high = Percent Detuned
28 deg° = Angle of Primary
68.43 ft = Length of Wire
0.499 inch = Average spacing between turns (edge to edge)
2.5 inch = Primary to Secondary Clearance
90.086 µH = Ldc-Low Frequency Inductance
0.02123 µF = Cap size needed with Primary L (reference)
373.534 µH = Lm-Mutual Inductance
0.2 k = Coupling Coefficient
5  = Number of half cycles for energy transfer at K
25.17 µs = Time for total energy transfer (ideal quench time)


Or alternatively, if I go away from the (nice) 
Maxwell .03 mfd pulse capacitor I am using, I 
have three other caps, each 10 kv:  0.5, 0.3 and 
0.3 mfd which I could run hook up in series 
giving me a total of .115 mfd (but only 30 kv 
total- I worry about that).  Reducing the primary 
turns to 5 would make this system:

Primary Outputs:
106.37 kHz = Primary Resonant Frequency
7.72 % high = Percent Detuned
48 deg° = Angle of Primary
27.48 ft = Length of Wire
0.753 inch = Average spacing between turns (edge to edge)
2.5 inch = Primary to Secondary Clearance
19.468 µH = Ldc-Low Frequency Inductance
0.09792 µF = Cap size needed with Primary L (reference)
184.788 µH = Lm-Mutual Inductance
0.212 k = Coupling Coefficient
4.72  = Number of half cycles for energy transfer at K
21.55 µs = Time for total energy transfer (ideal quench time)

I am concerned that these Chicago Condenser caps 
are not as well suited to Tesla Coil application, 
but is this the better approach?


Many thanks for your help, Terry.

Martin Fryml