RE: Awsome first light !! but...

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Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

>Original poster: "Edward Wingate by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <ewing7-at-rochester.rr-dot-com>
>
>Gary,
>
>I have run 1 and 2 turn primaries. Have you ever measured the discharge
>current from a cap into a 1 turn primary? Or the discharge current
>through a safty gap set at one inch and wired with #18 wire? 
>
>As I have stated on many occasions, the safty gap is just that, and is
>not supposed to fire unless there is a problem, and if and when there is
>a problem, you shut the system down.
>
>Ed

Hi Ed:

I've not tried to measure the current in a 1 turn primary but it's very
straightforward to calculate it.  All you need are the capacitance, cap
voltage, and inductance.  Peak current = Sqrt(C*V*V/L).  Since L is in the
denominator, you can see that as L gets small, peak current increases
rapidly.  With high peak currents come higher stresses on one's caps and
also higher gap losses.  For these reasons, low inductance primaries are not
generally used.

I wouldn't attempt to measure the current of a pulse cap discharging through
an un-ballasted safety gap unless I held a death wish for my test gear;-)
Putting it to a circuit simulator, my .02uF Maxwell cap has a .04uH ESL.
Assuming an initial charge of 20kV and guestimating a 2 Ohm gap resistance,
MicroSim tells me that the peak current will be 10,000 Amps, apparently
mostly a function of gap resistance.

You may well have the presence of mind to shut down at the first firing of
your safeties, but there are too many of us who will watch and listen in
denial, and who would materially benefit by including some form of
ballasting with safety gaps, even if it's just the primary inductance.  

Regards, Gary Lau
MA, USA