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Re: Transformerless Tesla coil



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
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

> The purpose of the network shown in my diagram was to solve two problems
> inherent in  driving a single end-grounded coil from a centre tapped HV
> transformer, firstly, to isolate the output resonator from the high voltage
> power supply, and secondly, to protect the transformer from damage due to
> common mode noise. The split MMC would solve the first problem but would not
> solve the latter.

Would reduce the common voltage level by 2.

> Seen from the ring -to -ground side the network is parallel tuned tank
> circuit of L1,L2,C2 and C3
> L1 is equal to L2  and C2 is equal to C3. It is only necessary that series
> tuned circuit of C1 and L3 be resonant at the same frequency as the parallel
> tank.

The impedance seen by the ring os ok, but this configuration charges
C1, C2, and C3 with identical voltages (see picture) before the gap 
fires. The correct initial conditions would be charges (+ above and
- below) in C2 and C3 only.
 
> Also, looking from the ring to ground side if a signal were applied at the
> resonant frequency, two equal antiphase signals at the same frequency would
> appear at HV1 and HV2 respectively. The resultant signals would be
> differential mode not common mode (unless I am mistaken!) The network is
> passive so in theory it works the other way too.

They would be common mode, as L1-L2 and C2-C3 form two identical
voltage dividers. L3 and C1 would have no influence, as they and
the transformer would be at the output of a balanced bridge.
 
> On the latter point of the uncertainty of whether both gaps would fire I
> have redrawn
> the diagram below to show a single gap across both of the HV rails- would
> this not ensure
> more reliable gap firing?

Just to see what would happen, I run a simulation of the entire circuit
using the values of a regular capacitive tranformer circuit L1a, C1a
L2a, C2a, C3a, with C1=C1a, L3=L1a, L1=L2=L1a/2, C2=C3=2*C1a, and 
the other elements as in the original. The oscillation
remains in C1-L3 only, with no energy transfer to the output...
And there is common mode voltage in the gap.
There is probably a way to design the network for correct operation,
but I doubt that common mode voltages in the gap can be eliminated 
with this structure.
 
                      +-----------to influence ring
                      |
                  +---+---+
                  |       |+
                  L1     C2
                  |       |-
    HV1----+--C1--+       +--L3--+
           | +  - |       |-     |
           |      L2     C3      |
           |      |       |+     |
    CT-+  SG1     +---+---+      |
       |   |          |          |
     GND   |        GND          |
           |                     |
    HV2----+---------------------+

Antonio Carlos M. de Queiroz