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Re: Proposed capacitive transformer TC?
Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
Tesla list wrote:
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
> Is C1 formed between the electric induction plane and the ground plane -or
> will supplementary capacitor need to be connected?
C1 is a discrete capacitor, as the primary capacitor in a regular coil.
> What is the function of L1 and why is it necessary- is it to resonate with
> C1 perhaps? I am asking because I envisaged the device I was describing as
> a capacitive autotransformer like a pi-tank or the tank circuit of a
> Colpitts oscillator (albeit without the feedback arrangements)
L1 resonates with C1, as in a regular Tesla coil. The tuning relation
the ideal system is L1*C1=(L1+L2)*C2. L1 must exist in a capacitor-
discharge system, to form the primary tank, where the energy initially
> Coupling is capacitive. Would it not be possible -in theory at least- to
> vary the coupling by varying the distance from the induction plane to the
> ground plane and topload without changing the ratio of C1 to C2 -although I
> surmise this would affect the resonant frequency somewhat.
The main effect would be to vary C2, as C1 is already a large discrete
capacitor, and extra distributed capacitance between the induction
plate and the ground would make little effect. The system can be tuned
in this way, given that L1, L2, and C1 are fixed. The equivalent of
the coupling would change too.
> Finally, could it be that the real advantages of this form of TC would be
> towards the higher end of the RF spectrum when coils are much smaller and
> more difficult to adjust than they are at low frequencies?
The coils can't be much smaller than the usual sizes, since they
operate with large voltage differences and enough clearances must be
kept. This causes also the distributed capacitances to be limited
to the regular values. But the coils can have less turns, with the
system operating at higher frequencies. The restriction is that at
some point it is not anymore possible to make a coil, since the
inductance becomes too small. See my directly coupled system for
example. The primary coil has 95 turns and the secondary has 1152.
If these numbers are reduced to 1/10, to 9.5 and 115.2 turns,
the system would (probably) operate in the same way, but the
operating frequency would rise 10 times (to 2830 kHz), and there is
still some way to go. The capacitances would remain the same.
Directly coupled systems, that include the capacitive transform
since they don't require a large (in size) primary coil, apparently
admit construction for operation at high frequency (a few MHz). There
is the problem with increased losses due to skin effect (use thicker
wire or tubes, since there is more space) and irradiation at these
frequencies (not so intense for the usual sizes). Something to try.
Antonio Carlos M. de Queiroz