Re: New NST-sync tests, was LTR Charging vs. Firing Time
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
> 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
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?
> John Freau