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Re: Continued Problems (fwd)
---------- Forwarded message ----------
Date: Sat, 23 May 1998 00:18:38 -0500
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Continued Problems (fwd)
Tesla List wrote:
>
> ---------- Forwarded message ----------
> Date: Fri, 22 May 1998 00:15:11 -0500
> From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Continued Problems (fwd)
>
> Malcolm (and all),
>
> Tesla List wrote:
>
> <snip>
>
> > > Just trying to understand this. I understand the tanks reactance is affected by added
> > > inductance and therefore the resonant frequency changes, etc... , but are you saying
> > > the secondary coil which has it's own reactance, would change due to an inductance
> > > change on the input side of the tank?
> > > Bart
>
> > <snip>
> > A crude model of the transformer primary + choke while connected
> > to the mains is that of the X of the choke at mains frequency
> > connected directly to the transformer primary since the mains is
> > effectively a short circuit (voltage source) in series with the two.
> > In this situation, the transformer is transforming the choke
> > impedance by the turns ratio squared to appear on the secondary side.
> > A simple example to illustrate using a transformer with a stepup turns
> > ratio of 1:2:
> > Let Vp = 1V and the reflected load cause a current
> > flow of 1A in the primary (assume no magnetizing current as this is
> > separate from the load current and may be made infinitesimal by
> > using a huge primary inductance). Then, Vs = 2V and Is = 1/2 Amp.
> >
> > Zp = 1 Ohm (1V/1A) and Zs = 4 Ohms (2V/0.5A) for Ns/Np of 2/1.
> >
> > One can model an equivalent circuit of the primary connected directly
> > to the mains and a choke appearing in the secondary side modified as
> > above. It is this effective choke that forms a resonant circuit with
> > the Tesla primary cap.
> >
> > Malcolm
>
> I understand the above. However (here it comes),in a case of a tuned coil where the xfmr is
> given added L (choke), Ls is seen as (xfmr L + choke L) x turns ratio squared. Tank C being
> fixed (IMO) causes a change in the tanks resonant F in relation to any change in L before
> the xfmr. Then, resonator vs. tank F would not be "tuned". The primary tap would then need
> to be re-tapped so that Lp = original XL = original F?
>
> Bart
Bart and all,
Assume that the main gap is across the HV transformer. In a resonant
charging system there are two independent resonant conditions at work.
The first condition, low frequency resonant charging, ONLY occurs when
the main gap is open, AND when the "effective" secondary inductive
reactance of the HV transformer is close [in magnitude] to the
capacitive reactance of the tank cap at the mains frequency of 50 or 60
Hz. As long as the main gap is not conducting, the tank capacitor
voltage and charging current will climb on successive mains half-cycles
until the main gap fires {or the transformer or tank cap gets overvolted
and fails). If the main gap fires, this "spoils" the Q of this resonant
system, and the resonant charging process begins anew once the gap is
extinguished. Ideally, the gap fires _at least_ once every half-cycle,
reducing the possibility of "letting the smoke out of your system".
The second condition occurs ONLY while the main gap is firing. In this
case the heavily-conducting gap effectively "shorts out" the transformer
L, leaving only the primary/tank inductance and capacitance to resonate
at the operating frequency of the coil. The HV source is effectively
"out of the picture", and will not influence the high frequency tuning
of your system. While the two resonant conditions are basically
independent and mutually exclusive, non-linearities (mostly transformer
or choke core saturation) may also introduce chaotic operation and
"bumping" in real-world coils...
-- Bert --