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chokes (and BIG Resistors) (power lost in RC)
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From: Jim Fosse [SMTP:jim.fosse-at-bjt-dot-net]
Sent: Saturday, May 30, 1998 12:32 AM
To: Tesla List
Subject: Re: chokes (and BIG Resistors) (power lost in RC)
>From: Gary Lau 28-May-1998 0733 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
>Sent: Thursday, May 28, 1998 6:54 AM
>To: tesla-at-pupman-dot-com
>Subject: Re: chokes (and BIG Resistors) (power lost in RC)
>
[snip]
>The bypass caps are being charged to the high secondary voltage only 120
>times per second, twice per 60 Hz cycle. I have yet to find a model that
>explains why the resistors get so hot. Still unclear to me is, with
>resonant charging (between the NST and the primary cap), how much more
>than the 60 mA rating of the NST is being drawn. 2X? 4X?
>
Gary,
The current in a parallel resonant circuit is Q times the
input current. In this case, we are talking about the leakage
inductance of the neon transformer, it's secondary resistance, the
added damping resistance you added, (+ filter inductance of ??) and
the C of the primary cap; ALL in a parallel resonance circuit. IIRC
Bert or Malcolm have measured Qs of 6 - 12 in this circuit. ergo: Iin
of 60ma => Iout = 60ma * (6 or 12) say 360ma to 720ma! So at 360ma
I^2*R (750ohms IIRC) => 97.2 watts! double that for a Q of 12. I'd
guess that your resistor run hot. (engineers, please note that this
discourse does not include the effects of the spark gap shorting out
the resonant circuit which will, by inspection, lower the
dissipation.)
Hum, a question for Terry Fritz - have you considered scoping the
primary circuit's current waveforms for this effect with your fine
measurement setup?
aside: All, note that a 1 watt resistor will dissipate 1 watt but,
it's temperature will be 200 degrees Celsius above the ambient
temperature! That is how resistors are rated. I guarantee burnt
fingers, if you run a resistor at it's rated power level and touch it.
chills ;)
jim
p.s. at stp in air of course.