Re: Need TSG help

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Steve,

Ouch! 

Have you tried increasing the distances between the main electrodes and
trigger electrode in the TSG's? When one gap fires, there's a very large
dv/dt at the common tank capacitor connection (the triggered spark gap
behaving much like a "sharpening gap"). The sudden 15 kV change at the
other TSG terminal may be causing breakdown between the other TSG's common
electrode and its trigger electrode, since the trigger electrode voltage
can't instantaneously change to keep it "centered" at half the potential
across the main gap. In addition, parasitic HV RF floating in the circuit
when one gap fires may add to the voltage stress such that setting the gaps
to reliably trigger without cross triggering may be very difficult. 

Some possible fixes:
If you haven't already done so, make sure that light from one gap is
prevented from being "seen" by the other so that UV from the triggered gap
doesn't stimulate breakdown of the other TSG. One other possible option is
to change the gap geometry somewhat and modify the trigger circuits to
generate consistently polarized HV trigger pulses. With proper set up, you
should be able to preferentially overvolt the larger gap BC when you
trigger the desired gap, causing cascade breakdown of gap AB on the desired
gap. With a larger BC gap, you should be able to avoid overvolting gap BC
on the other TSG. 
 
        --   Trigger pulse
       |  |
    ---    ----
      ----------
                |
      -----O    O         O ------  
           A    B         C      |
  +7.5 kV                        |
                                 |
                                 |  |  |
    --    ---                    o--|  |-----OOOOOOO---
      |  |  Trigger Pulse        |  |  |              | 
       --                        |                    |
     -----------                 |                    |
                |                |                To -7.5 kV
      -----O    O         O ------  
           A    B         C
  -7.5 kV    


Good luck!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<youngs-at-konnections-dot-net>
> 
> To TSG Engineers & experimenters,
> 
> I need some advice.  I have a 15 KV DC supply which charges a series
> connected primary LC tank circuit via one spark gap, then discharges the
> tank LC via a second spark gap.  Basically, it is a SPDT switch.  The RSG
> version of that I call the Deanogap which I have described in previous
> posts.  It works really well and no power wasting series resistor or other
> ballast is needed.
> 
> I tried replacing the RSG with two TSGs, alternately fired by two HEI coils.
> Each TSG is three copper pipe couplings, with the trigger applied to the
> center one through 5 .001 mF 10 KV caps in series.  The center electrode is
> biased at mid-voltage by resistor strings.  The circuit is +7.5 KV to one
> TSG and - 7.5 KV to the other TSG.  The other ends of the TSGs are connected
> together and to the tank cap.  The other end of the tank cap connects to the
> primary.  Finally, the other end of the primary goes to the -7.5 KV.
> 
> Here is the problem.  When one of the TSGs fires, it immediately causes the
> 2nd one to fire.  Both of them firing at once is really bad news!  It
> results in a deafening, frightening BANG!! as several hundred Joules of
> reservoir cap energy is discharged through the two TSGs in series!  Very
> hard on caps, power supply and my nerves, and no energy makes it to the
> secondary.
> 
> I suspect it will be difficult to impossible to prevent this from happening,
> but I thought I would try the wisdom of the list before abandoning the
> design.  Any ideas on how to prevent each TSG from causing the other one to
> simultaneously fire?
> 
> --Steve