Re: New NST-sync tests, was LTR Charging vs. Firing Time

Hi John,
         I can't speak for computer simulations except those in my 
head but from experience I can say that I have never had a smoothly 
firing LTR system with a static gap. I am currently building a sync 
rotary so hopefully I can catch up with some of your work. At the 
least the sync gap appeals because it can force firing according to 
mains frequency charging.

> I decided to set up the system to be similar to Terry's, except I used
> a 12kV, 30ma NST, and a .0147uF cap.  This cap is about 2.2 times
> the reso-cap size, which is the same ratio that Terry uses, I think.
> I figured this should give scope results that are similar to his.
> When I first installed the NST and tested the system, the first thing
> I noticed was that it ran very poorly.  At the usual gap phase setting,
> the waveform dipped a lot (?), then fired while it was strongly rising,
> well before the cap voltage peak.  The power factor was bad and the 
> operation was inefficient.  It needed a radical shift in the
> sync gap phase.  My PT system ran best at around 60 degrees
> ASVP (After the Supply Voltage Peak).  Terry's works best at 75
> degrees ASVP.  This new setup worked best at 135 degrees ASVP.
> At this setting, the voltage gradually rises then peaks, and fires at
> or slightly after the peak.  At this setting, the voltage rise, the
> and the power factor (with PFC) seem as good as with the PT.  If I
> set the phase a little earlier, the voltage rise is greater, but the gap
> stops firing suddenly as the variac level is increased.  If i set the
> phase a little later, the voltage rise is less.  I did not expect this
> 135 degree ASVP phasing requirement.

Again I think if you compared the desirable firing angle with the 
resonant frequency of the cap and transformer leakage inductance you 
would find a correspondence. If not, there would appear to be 
something else to learn that has not been taken into account.

> In any case, I tried adding some external ballast, but the more
> I added, the more the output decreased.  This agrees with Terry's
> findings. 
> I also noticed a wavyness in the charging waveform, I'm not yet sure
> if this is real, or just some type of interference or meaningless
> resonance.

See above. Please keep us posted. Great work as always.


> I'll do more tests to try to find a good gap phase setting near 60 or 75 
> degrees ASVP that causes a small dip, and then a proper rise.
> Maybe I missed it.  Here are more speculations:
> 1.  There may be two modes for LTR sync operation?  In this new mode,
> the firing point is quite critical.  Imagine what this would do using a
> static gap?  The efficiency and power factor would bounce all over
> the place, maybe this is why this system doesn't work well with a
> static gap.  There is really only one phase position where the coil
> works well, the likelihood of the static gap firing at this point is poor, 
> especially since the firing should occur after a voltage plateau.  The
> sync gap permits this, the static gap won't.
> 2.  Why does Terry's system work more like the PT setup?  Does
> the greater robustness (or the nature of the shunt) of a 15 - 60 NST
> make it behave more like a PT?  Could this explain
> why Gary's static gap system works well and mine does not?
> Does the gap phase need to be moved to this new regime when 
> the cap gets too large even using a 15 - 60 NST?
> 3.  Are these new results real or did I make a mistake in any of the
> above work?  What causes the need for this new phasing regime? 
> Do the computer simulations show effects such as I am seeing?
> Thanks,
> John Freau