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chokes (and BIG Resistors) (power lost in RC)
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From: Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent: Monday, June 01, 1998 11:52 AM
To: Tesla List
Subject: Re: chokes (and BIG Resistors) (power lost in RC)
Tesla List wrote:
>
> ----------
> 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.)
>
Except that the 97.2 watts isn't 100% duty cycle. That is the peak
power during the ringing (assuming you aren't resonating at 60 Hz). If
the damped pulse lasted 10 cycles at 100 kHz (i.e. 0.1 mSec), your duty
cycle is only 0.1/8.33 or about 1.2%, for an average power of about a
watt.
Also, given the typical DC resistance of a few K for a NST secondary, a
secondary current, resonant or otherwise, would imply a dissipation of
several hundred watts inside the NST.
That power being dissipated has to come from somewhere. What does the
primary power measurement show. If you have a 450 VA NST, if you
perfectly match the output so the power factor is 1, you'll have a total
power consumption of 450 Watts, some fraction of which is dissipated
internally, and some fraction is going to your load.