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Re: Triggered gap hookup question



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

Weazel,

Sorry for the delay in responding...

Assuming your isolation transformer has a high enough breakdwon voltage,
you could remove capacitor C2, and then connect the common line from the
ignition coil primary to one of the HV outputs of the RADAR transformer.
However, this will float your entire ignition coil and trigger circuit to a
high AC potential. This approach should NOT be used unless you have a
specially insulated HV isolation transformer that can handle the worst case
HV from the RADAR transformer.

A safer alternative is to "create" a center tap by using a pair of HV
resistors of equal resistance connected across the output of your RADAR
transformer. This provides a return path for the triggering current to
flow, while letting the trigger circuit remain at near ground voltage. The
HV resistors must be able to withstand at least 0.5X of the peak output
voltage from your RADAR transformer (but I'd go with 1X for each resistor).
Use either series connected chains or resistors or "tiger stripe" 10-15 kV
HV resistors. You could also add small HV capacitors (100-250 pF) across R3
and R4 in order to increase the trigger pulse current to provide more
reliable triggering. 
          
                      C4                   C5              R3 = R4 
                      ||                   ||              C4 = C5
              |-------||---------o---------||---------|
              |       ||         |         ||         |
              |                  |                    | 
        H1    |        R3        |          R4        |     H2
        o-----o-----/\/\/\/------o-------/\/\/\/------o------o
                                 |
                                 |
                                 |
                To C2            |
                    <------------|


Good luck, and safe coilin' to you!

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


Tesla list wrote:
> 
> Original poster: "J. B. Weazle McCreath by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>
> 
> Hello coilers,
> 
> Refering to Bert's drawing below, where do I connect the right
> hand end of C2 in my setup?  My radar transformer doesn't have
> a grounded center tap on the secondary as is the case with NST
> or OBIT type transformers.  My trigger circuit is powered thru
> a 240:120 isolation transformer, hence the can of the ignition
> coil basicly floats and can be connected anywhere, such as the
> grounded electrode of my safety gap.
> 
> The entire primary circuit floats above ground, with the only
> ground being the center electrode of the safety gap, which is
> part of my Terry style filter.  The filter is constructed on
> single sided G-10 circuit board with the copper foil being the
> ground for the doorknob bypass caps.  I do it this way so I can
> use different transformers without a major rewiring job...just
> two or three spade type connectors.
> 
> 
>       Dimmer
>       |----|    | |
>   <---|    |----| |-------
>       |----|    | |       |    Ignition              (optional)
>                           |      Coil                    R1
>                5-10 uF    |    -------             |--/\/\/\/\---o
>  To             (C1)      |----|     |             |
>  AC                            |     |    | |      |        Trigger
>  Mains                         |     |----| |------o------------->
>  (isolation                    |     |    | |      |
>   trans. in           Common   |     |             |
>   my case)                |----|     | 100-500 pF  |--/\/\/\/\---o
>                           |    -------  30-40 kV         R2
>                           |              (C3)       (optional)
>                           |
>                           |
>                           |                 | |
>   <-----------------------o-----------------| |-----> to case/CT of
>                                             | |       NST & AC mains
>                                                       ground
>                                            1-5 uF     (where to in
>                                           600 volts    my case?)
>                                             (C2)
> 
> Thanks in advance for your help and/or suggestions.
> 
> 73, Weazle, VE3EAR/VE3WZL
> 
> Listening: 147.030+ and 442.075+
> E-mail:    weazle-at-hurontel.on.ca
>            or ve3ear-at-rac.ca
> Web site:  www.hurontel.on.ca/~weazle

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