RE: Triggered gap

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

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

Hi All,

 A note here that some may overlook,

 A triggered gap basically waits for the user to fire it (by turning on the
dimmer).  So it's holdoff voltage is higher than the peak voltage of the
circuit, else it would just be a plain static gap, only set very wide.  I
*highly* recommend running DC to the cap for this, to eliminate the dangers
of resonant rise.  if you run a resonant setup on a triggered gap and your
dimmer cooks from kickback, the voltage will skyrocket till the tranny or
cap bites the Big Electron.  If you're running DC, it'll only charge to the
tranny's peak voltage and then sit there patiently waiting.  The diodes
shold be suited for handling the kickback of the trigger voltage (my 40kv
diodes have held up fine so far).

  The diodes are cheap when bought from digikey in bulk (I use 1n4007's,
1kv1A)  It saves a lot of worry about blowing the caps from reso-rise.  For
me, it's peace of mind that my Maxwell won't blow. ;)
														Shad

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Thursday, April 19, 2001 1:58 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Triggered gap
>
>
> 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)
>
> Cheers,
>
> Alex
>
>
> On Thursday 19 April 2001 15:20, Tesla list wrote:
> > Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> > <Hhchicken1-at-aol-dot-com>
> >
> > Hi list!
> > I have decided to make a triggered spark gap to replace my
> current 'vice
> > and a nail'.  I thought I'd better post to the list before
> I fry myself...
> > For the initial tests I will be using a NST labelled 6/35,
> although it
> > seems to be able to jump a gap of more than a centimeter
> (!). For the gap
> > electrodes, I am using the Earth pins from UK mains sockets
> - I believe
> > they are made of copper, and they are much more substantial
> than the US
> > variant. I have set two of them up at a distance where the
> NST with tank
> > cap attatched will not bridge the gap, and have placed a
> third trigger
> > electrode in the middle, offset by quite a large amount, so the gaps
> > between any two electrodes are about equal.  With the NST
> and tank cap (no
> > primary), this does not fire.
> > For the trigger, I am using a car ignition coil powered by
> a dimmer switch
> > and 3uF cap direct from the 240v 50Hz mains.  This produces
> (at a guess)
> > around 40kV and when fired across a gap produces a tone
> that sounds quite
> > like 50Hz.  I am all set to connect this to the main gap,
> but am unsure how
> > to safely do it.  As the ignition coil is an
> autotransformer, if I connect
> > the HV out from the coil to the trigger electrode, and the
> minus terminal
> > on the coil (which is also connected to my dimmer) to one
> of the other
> > electrodes, surely I will be almost directly connecting the
> HV from my NST
> > to my dimmer switch?  Another problem is that my NST is not
> grounded, I
> > realise that this is a must and will do that before I try anything.
> >
> > Thanks for any help you can give me - a schematic would be
> handy hint hint
> > :) Henry Hallam
>
>
>
>