RE: Triggered spark gaps for coils

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

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



>Original poster: "Metlicka Marc by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <mystuffs-at-orwell-dot-net>
>
>> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
><Gary.Lau-at-compaq-dot-com> 
>> Commercial triggered gaps are typically used for laser applications where
>> the delay from the trigger pulse to gap conduction matters and is
measured
>> in nanoseconds.  We can tolerate tens of microseconds of jitter and there
>> will be no observable impact to performance.  I doubt that any realistic
>> environmental variation short of flooding is going to make any difference
to
>> us.  And it can have no more impact than in conventional RSG's.
>
>i thought that moisture might cause a premature triggering of the gap
>before the pulse?
>good to know that once it is set it should be stable, any ideas on gap
>spacing as per voltages, like 1/3 rd more then self triggering?

A triggered gap can't be prematurely triggered by humidity unless the
electrode spacing is right on the hairy edge of its static breakdown
voltage, which it should not.  I'm not even sure humidity will be a
significant factor as air pressure is.  It is however an interesting
question - how to set the main electrode spacing.  It should be some margin
above the peak cap charging voltage.  However, you can't just not trigger
the gap and see at what point it won't fire by itself, as it will ring up to
higher and higher voltages on each unfired half-cycle.  We may have to just
run it with triggers and gradually close the gap until it fires irregularly,
then open up a bit.
 
>oh, i must have totally misunderstood the air quench gap idea? i
>automatically see compressors blowing the arc out.
>i have a nice high velocity turbine type blower that i may be able to
>play with. would it be better to draw through the cylinder containing
>the gap or blow through? in jim's post he mentions air passing over the
>annular trigger electrode as well as through the cathode, maybe it would
>be very easy to set it up along the lines of a flow bench, drawing
>through a ventury with paths along various parts for cooling.

This is just one of those areas that's wide open to innovation with no
standard for what's the best configuration.

>basically our sync. gaps are firing at various points of the waveform
>now, i would think that as long as your firing at a point where the tank
>is charged to peak then that would be optimum? i may be missing things
>here. i've had little luck finding much as way of search's for triggered
>gaps other then eg&g. 

This is counter-intuitive, but the optimal point at which a sync gap should
fire is not necessarily when the peak cap voltage is reached.  For a LTR cap
size, the best point is after the peak voltage.  A smaller than resonant cap
wants to be fired somewhat before the peak voltage is reached.  Microsim
simulations bear this out, but we don't have to be this analytical in
practice, we just have to turn a knob to vary the trigger delay until the
longest sparks are reached.  But the point is, the firing time should not be
determined by looking for a peak cap voltage, but rather just a simple
variable time delay from the mains zero voltage crossing.

>i wonder if the modified strobe circuit that terry
>rigged for phasing sync's could be a simple starter trigger? how much
>current does it look like would actually be needed to get ignition?
>would this be a factor of the arc channel diameter of the tube
>containing the gap? 

I took a look at Terry's modified RS strobe.  It only fires at 60 Hz (we
need 120Hz) and saw no obvious way to vary the phase in a reliable way.
It's not referenced to zero crossings and will be unstable with changes in
line voltage.   I'm not sure I understand your current question.  As long as
your trigger coil makes a spark, it's good.

>i have a BUNCH of gas tube surge suppressers rated for 250v each, maybe
>for starters i can gang some up for 3kv each side and trigger the center
>to try to get a little of the trigger circuit expierience(out load
>thinking)

I think as long as you can get your test circuit to make a 1/4" or so spark
in the air at 120 Hz, you've accomplished your goal.

Regards, Gary Lau
Waltham, MA USA