Re: LTR Charging vs. Firing Time

In a message dated 99-06-21 10:48:36 EDT, you write:

<< Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> Hi All,
> 	I ran a computer study of charging voltage vs. firing time delay of my
> sync gap.  LTR coils tend to perform better if the gap fires later than the
> peak voltage occurs across the main gap.  This allows the inductive kick
> charging (IKC) to work a bit more efficiently.  The results of the study
> are as follows:

Terry, all,

Thanks for these results.  In your NST powered system, since the 
leakage reactance is fixed, you can vary only the sync phase timing.
In my system using the external ballast and potential transformers,
I can vary the ballast inductance also, which permits me to fire at
any sync phase without overshoots.  This may permit more fine
tuning of the system.  By not having an adjustable ballast, the
complete picture might not be seen.  I guess a variable external
ballast can be added to the simulations, if it's not already there.
More below.  

You may be able to accomplish this in some cases by either 
using an extra external ballast, or by changing
the cap size.  The downside is it adds still more variables.  But
this may be especially useful with static gaps, and may explain
why some static gap systems work better than others (overshoots
are eliminated).  Overshoots seem to ruin the power factor a little.
> Delay = Delay time in milliseconds referred to the AC line voltage.  About
> 21.6 degrees per millisecond.
> Firing Voltage = The voltage at the firing time in kV.
> Overshoot = The peak voltage of the waveform in kV.  The gap can fire after
> this peak.
> Delay	Firing Voltage	Overshoot
> 0.0	4.02		7.50
> 0.5	7.76		-
> 1.0	11.22		-
> 1.5	14.28		-
> 2.0	16.83		-
> 2.5	18.80		19.03
> 3.0	20.06		20.98
> 3.5	20.67		22.51
> 4.0	20.45		23.48
> 4.5	19.63		23.81
> 5.0	17.95		23.46
> 5.5	15.81		22.43
> 6.0	12.91		20.77
> 6.5	9.75		18.53
> 7.0	6.04		15.81
> 7.5	2.30		12.76
> 8.0	1.44		9.54

Interesting,  I never thought of delaying the firing by more than 90
degrees, although it doesn't seem to give more peak cap voltage 
> So the optimum firing time for my coil is 3.5mS after the AC line voltage.
> This works out to 0.0035*60*360 = 75.6 degrees (I have incorrectly quoted
> this in older posts as around 30 degrees).  The peak voltage can reach 24kV
> as I am playing with the timing of the rotary sync gap.

Because of your fixed leakage resistance and cap size, it would
seem to me that the firing point is a compromise.  If you add some
extra external ballast, you may be able to make the coil fire at the
peak cap voltage at 75 degrees.  I fire my gaps at the peak cap
voltage, and obtain the same IK peak cap buildup, by adjusting
my ballast as needed.
> A static gap should fire around 2.5 mS but would not be as ideal as a sync
>gap that could fire a millisecond later.  Perhaps this explains the success
> of using static gaps with LTR caps.  However, they would only get about 70
> percent as much power per given input.

With proper ballasting, or perfect leakage reactance/
cap size IK match, a longer delay may be achieved because 
overshoots will be eliminated.  It may also explain the great need
for gap cooling with static gaps...cool gaps
fire later, and help keep the system within the IK domain.  Perhaps
proper ballasting can even reduce the degree of firing chaos in 
static gaps, although I think someone did a simulation that suggests
it cannot?

Also, the IK buildup can be obtained even with the ballast set to
cause the gap to fire before the peak cap voltage, in fact this seems
to cause an even greater IK voltage buildup, but some tests showed
a poorer power factor (another test didn't).  Needs more testing.  But
in any case, this should permit the static gaps to show a strong IK

More in my other posting.

John Freau
> I should also note that the voltage rise across the capacitor after the gap
> fires does rise fairly linearly at first and the current remains fairly
> constant supporting the idea that the neon is acting like a current source
> during this time.
> I posted a MicroSim graph of the firing voltage and neon currents before
> and after the protection filter at:
> www.peakpeak-dot-com/~terryf/tesla/misc/LTRIKC.jpg
> Cheers,
> 	Terry