[Prev][Next][Index][Thread]

Re: Safety Gaps

Hi Viv,

	So, your running a sync rotary gap with resonant rise and lots of safety
gaps.  However, you are not able to limit the arcs to just the main gap.
The safety gaps still fire.

	First of all, do -->NOT<-- open the safety gaps!!!!  That won't fix the
problem it will only risk blowing the neons again :-((  There is something
else wrong.
	
	You have rotated the gap phase so that you get a maximum of arcing in the
main gap but you can't "tune" out the safety gap firing completely.  You
realize that the main gap phase may be shifted by the resonant circuit in
the primary.  You may have to search around to find the best place to set
the gap phase.  Mine is almost 30 degrees away from where a strobe disk
says the input AC mains is.

	There is a chance that there is something going on in the filter circuit.
Those Ls and Cs and other "stuff" used in neon protection filters can cause
small resonances too.  These may be acting up with your system and causing
voltage spikes.  I can't determine this without knowing a lot of funny
parameters.  But no problem...  I think the problem is far simpler. 

Please see Gary Lau's wonderful web page and especially the following:

http://people.ne.mediaone-dot-net/lau/tesla/gapsim.htm

	His first simulation shows that with resonant rise, the primary cap is
able to charge to firing voltage many times during a single AC cycle.  Of
course, that is the problem.  Your sync gap fires during ONE of these at
each cycle (actually twice per full cycle but you know what I mean :-)).
However, when the cap recharges AGAIN on the SAME cycle, your sync gap is
out of position.  It can only fire once per cycle but the cap can charge to
firing voltage two or three times per cycle.  The safety gaps are acting
just as they should to save you neons from destruction! :-))

	So, you have a main gap firing at 100 times per second (UK) and a main cap
charging at maybe 250 times per second.  What do you do?  I would say join
"Terry's club" :-)) and add much more capacitance (I never have liked
resonant charging at all...).  Add so much darn capacitance that the
charging rate is brought down to the same rate as the sync gap can fire at.
 Don't be surprised if that is 3 times your present capacitance!  Thus, the
LTR thing...  When you have added so much capacitance that the safety gaps
"just" fire at full input (with the primary connected) you are at the first
stage.  However, you will find that you can still add more capacitance and
the system will still charge to full voltage if you set the sync gap right.
 That is the effect caused by the resonance of the system.  I wish there
were a simple way to explain this effect.  It is complex.  However, the
bottom line is if you add so much capacitance the resonant rise is
eliminated, you will charge the primary cap to full voltage 100 times per
second and you sync gap will hit that point just right.  You will like the
results!!

	In the mean time.  Just don't turn up the power above 50%.

	Hopefully, I will get a paper on LTR caps out in a few weeks that will
explain this.  I am collecting parts to make a "ground up" LTR system now
to demonstrate the design...

At least that is my idea on all this...

Cheers,

	Terry




At 09:49 PM 5/17/99 +0100, you wrote:
>Hi All,
>    I know this has been asked many times as I've read previous posts but
>I'm having difficulty setting my safety gap with my rotary.  You may recall
>I blew my Neon a while ago while running my new Sync rotary so I don't want
>to do the same again.  I tried setting the S-gaps so they just don't fire
>with no primary circuit connected.  However connecting the primary circuit
>causes the S-Gaps to fire at about 50% input voltage and no main gap
>running.  So I assume I'm getting resonant rise and the S-gaps then fire.
>However when running the rotary the S gaps still fire at 50% input.  I tuned
>the Rotary phase with about 5% input voltage to the primary and rotate the
>rotary phase to the centre of max arcing range.  This seems to correspond
>with the electrodes lining up with the white part of a strobe disc I had
>attached.
>
>My safety gap is standard, with a separate gap from each HV terminal to
>ground.  Also a separate gap across the rotary.  All are 1/4" brass round
>nose shape.
>
>I originally set the S-gaps to 1/4" with the rotary S-gap at 1/2".  With no
>main gap the safeties did not fire so being worried about over-volting I've
>closed the gaps down  as described above.
>
>I'm now running two 5KV 120ma Neon's in anti-phase with centre ground.
>
>regards
>
>Viv Watts UK.
>