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Re: RC filter
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- Subject: Re: RC filter
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Mon, 14 Mar 2005 20:07:30 -0700
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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
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?
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> 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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