Re: Triggered gap

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Alex Crow by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<alexcrow-at-blueyonder.co.uk>
> 
> Stop!
> 
> Do not run your transformer and cap together without them connected to a
> coil! The reason you are jumping 1cm is due to resonant rise, which is
> ringing up the voltage on the NST - you risk it arcing over and destroying
> it, plus the caps!
> 
> You must test the initial gap spacing with the NST *only*. This way you will
> be able to determine the precise spacing at which the rated voltage won't
> arc. You can then increase this by, say, 50% and place it in circuit with the
> triggering set up. If the gap overvolts, it should fire without a trigger and
> thus save your NST, but if optimally triggered it should then run as you
> desire.
> 
> Note that you may want to feed the trigger electrode via a small high voltage
> cap, say a few tens of pF (any others have an idea here?) so that kickback
> will be at low current and be filtered out by the Ign. coil. Then you won't
> end up frying the dimmer! (Some sort of snubbing might be useful on the
> dimmer o/p if it's not there already)


The auto ignition coil is pretty high impedance (both at RF and DC), so you
can probably not bother with the coupling cap.  In actual use, the auto
coil sees high frequency transients (albeit not at hundreds of kHz), and
they are pretty tough devices. Don't make the gap from auto coil output to
triggered gap electrode too big.  Even though the coil CAN put out 40 kV,
you don't need that much here, and there's nothing to be gained by
stressing the coil dielectric.  The triggering mechanism is that the spark
from the coil creates a huge flood of ionized particles in the gap,
distorts the field, AND irradiates it with UV, all of which cause
breakdown. None of this needs a huge long spark.

FWIW, sub-$1 xenon flash trigger transformer might also work in this
application, although they are much more delicate device.