Re[2]: RC filter

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Original poster: Sebastiaan Draaisma <sebas@xxxxxxxxxxxxxxxx>




Chiang Mai, Tuesday, March 15, 2005


In reply to: RC filter

Posted on: Tuesday, March 15, 2005


Hello Gary,

Thanks again,

This is very interesting all trough I'm wondering how you measure the 
actual output of the NST, I don't have, and am not familiar with a scope. 
Can it be done by measuring the primary with the power factor correction 
connected to it, measure the actual power consumption and convert that back?


For example I measure on the primary of my 230V - 15kV 30mA NST a current 
of 3.26A, which would equal 750W and convert that back to the secondary

750W / 15000V = 50mA. Or would this not work?


Best regards,

Sebastiaan Draaisma


Tesla> Original poster: "Lau, Gary" <gary.lau@xxxxxx>


Tesla> Hi Sebastiaan:


Tesla> Sorry for the delay - I found this reply languishing in my Drafts

Tesla> folder...


Tesla> The easy answer is that the choice of R-C filter caps does not affect

Tesla> the needed value of the tank cap to achieve pri-sec resonance.


Tesla> Estimating the power dissipated in the filter R's is more challenging.

Tesla> There are two components to this (as far as I'm aware).


Tesla> One component is, by Ohm's law, the current from the NST squared, times

Tesla> the resistor value.  But the catch here is knowing what the NST current

Tesla> under actual operating conditions is.  I have a 15/60 NST, no

Tesla> modifications to the current limiting shunts.  But I've measured in

Tesla> excess of 150 mA RMS when running.  Such high currents are possible when

Tesla> Variac-ing up the NST primary voltage and when using high tank cap

Tesla> values, but is not well understood or predictable.  For my coil, I use

Tesla> 1.7K series resistors, so .15*.15*1700 = 38.2 Watts per resistor.


Tesla> The second component is determined by realizing that the power in the

Tesla> bypass caps is dissipated in the resistors each time the main gap fires.

Tesla> The larger the bypass cap is, and the higher the main gap BPS is, the

Tesla> more power is dissipated here.  For my coil, I have 450pF caps, and the

Tesla> bang voltage is about 25kV.  Each of the two bypass caps is charged to

Tesla> 25kV/2 or 12.5kV, 0.5*C*V*V = .0351 joules.  With my 120BPS sync gap,

Tesla> this will dump 120*.0351= 4.2 Watts into each resistor.  If I were to

Tesla> use a static gap, this would have a higher BPS, but possibly a lower

Tesla> charging voltage; not sure if the power would be higher or not.


Tesla> So I'm guessing my resistors each dissipate about 42.4 Watts.


Tesla> Regards, Gary Lau

Tesla> MA, USA


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