Re: Triggered gap

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

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

Henry and all,

Because of the direct connection that most ignition coils have between the
bottom of the secondary, core, and one end of the primary circuit, I'd
recommend adding a coupling capacitor in the primary circuit (C2) and
adding a HV blocking capacitor (C3) in series with the HV output from the
coil. This is the approach I used to prevent potentially devastating back
current from flowing out of a large capacitor bank during triggering a
quarter shrinker. Use a fixed font (Courier) to view the ASCII drawing
below. The actual values of C2 and C2 are not very critical, but use the 
minimum voltage ratings as shown. 

C2 provides a clean path back to the center point of the NST, effectively
"clamping" the common point of the coil to ground for the HV discharge path
while blocking low frequency AC mains current. Capacitor C3 should be a
30-40 kV "doorknob" cap - its job is simply to provide a path for the HV 
triggering pulse while blocking significant low frequency currents from 
"backing up" into the ignition coil. BTW, if you use a true field 
distortion gap, you'll also need a pair of HV (~15 kV) resistors to 
"balance" the voltage at the triggering electrode between that of the main
gap electrodes. However, if you are simply using an off-axis trigger wire 
(such as Marc's gap) R1 and R2 will not be necessary. 
 
                         
      Dimmer       
      |----|    | | 
  <---|    |----| |-------
      |----|    | |       |    Ignition              (optional)
                          |      Coil                    R1
               5-10 uF    |    -------             |--/\/\/\/\---o 
                (C1)      |----|     |             |                
                               |     |    | |      |        Trigger
 To                            |     |----| |------o------------->
 AC                            |     |    | |      |           
 Mains                Common   |     |             | 
                          |----|     | 100-500 pF  |--/\/\/\/\---o 
                          |    -------  30-40 kV         R2          
                          |              (C3)       (optional)
                          |
                          |
                          |                 | |
  <-----------------------o-----------------| |-----> to case/CT of
                                            | |       NST & AC mains
                                                      ground
                                           1-5 uF
                                          600 volts 
                                            (C2)

Hope this helps!

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



Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Hhchicken1-at-aol-dot-com>
> 
> Hi everybody,
> Today I'm going to connect up the gap as specified in Marc's schematic at
> http://63.229.238.60/temp/trigger_sch.jpg. I'll let you know what happens.
> The only thing I am worried about is that while the trigger spark is on, does
> is provide a conductive path from the NST through the ignition coil to my
> dimmer switch?  Or does the choke effect of the coil prevent this?
> Thanks, Henry