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Re: NSTs and Cap Charging.
Malcolm -
Your example is typical of what every coiler is faced with when designing
a coil. Unfortunately the coiler using these calculations only ends up with
a fictitiious solution. In your example the 720 VA NST rating cannot be
compared to the 565 joules and 462 joules rating of the primary capacitors.
Comparing power (VA) ratings with energy (joules) ratings requires that time
periods and efficiencies must be taken into consideration.
Actually the 720 VA rating would probably never be realized in Tesla coil
operation because the TC load reduces the voltage and, therefore, the VA
rating. The 565 and 462 joules in the capacitors is a random condition that
varies with each bang as shown by the waveforms. This means that for each
bang you would have to know the instantaneous input watt seconds and the
instantaneous capacitor joules for that particular bang and that particular
coil operating at that particular condition.
However, for the overall picture of the TC operation the major TC
parameters can be estimated using the proper equations and data from real
coil tests. This makes it possible to develop a TC computer program like the
JHCTES program. This program has been found to be resonably accurate and can
be easily adjusted to conform with new test data as it is received. The
program does not include operating spark gap conditions because there is not
enough proper empirical data available to include in the program at this time.
John Couture
-------------------------------
At 11:53 AM 4/9/99 -0600, you wrote:
>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>
>Further to the discussion on resonant charging, I decided to run
>some figures through the mill to see whether one really could do
>better than the VA faceplate rating. NB - this is not modelling,
>just looking at the calculations. For this purpose, I've assumed that
>the experimentally determined value of cap that appears to give best
>results is 2x the resonant value and gets charged to SQRT2*Vrms. I've
>further ignored the consequences of opening the gap up to 2.22*Vrms
>for the resonant case.
>
>A typical transformer: 12kVrms, 60mArms, Fmains = 50Hz, BPS = 100.
>
>VA rating = 720
>
>Case 1: resonant charging
>
>Based on V/I = Zcap, Cp = 15.92nF
>If gap is set to 26.64kV (assume no losses), then Ec = 5.65J roughly
>so power = 565W, less than the VA rating.
>
>Of course one wouldn't normally open up the gap to this extent so one
>might assume that you get firing at 2Fmains at Ec = 2.3J which means
>a throughput of 460W or so.
>
>
>Case 2: larger capacitor
>
>Let Cp = 32nF and assume it charges to 17kV in a half cycle.
>Then Ec= 4.62J and throughput = 462W.
>
>In neither case is the VA rating of the transformer exceeded.
>Comments? Flaws?
>
>Malcolm
>
>