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Scoping and cap charging
Original Poster: FutureT-at-aol-dot-com <mailto:FutureT-at-aol-dot-com>
>In my reso-cap days, I used to just rotate the motor for best spark
>length, starting at low power to prevent the zero cap voltage at
gap
>presentations, then crank up the power and rephase as needed at
>full power. I like to place a numbered dial onto the motor cradle,
with
>a pointer on the motor. The proper phase settings can be made
>into a chart that shows the proper phase settings for various
>sized caps, NST's, etc. Now of course I'm observing everything
>on the scope, but it's not necessary, but really nice to see.
Hi John:
With a NST system, how does one scope the cap charging voltage? Even if
using a high voltage probe, it still needs to be referenced to ground, and
neither side of a cap is typically grounded. I really need to see what my
static gap BPS and charging voltage is.
>In any case, even if you started the system at zero cap voltage
>at presentations there would probably be no problem, because
>with LTR caps, the voltage remains lower when the gaps are not
>firing than when they are firing. It doesn't matter if
presentations
>are missed, etc. This is still another wonder of the LTR - IK
set-up.
>
>I'm beginning to think that the large cap you're using is letting
>the inductive kick effect occur strongly in your coil. Terry's cap
>voltage peaks somewhat before his gap firing at 75 degrees. But
>your larger (?) cap should delay the peak to perhaps around 50 to
>60 degrees (?). You may be getting as much cap voltage as if you
>were using resonant charging. I may look at this more if I get the
>chance.
>
>Cheers,
>John Freau
Don't forget, I'm using a static gap, so my firing voltage is the same as
with my reso-cap, and I suspect my gap firing is happening at random and
chaotic intervals. But there is certainly something strange going on. I
just metered my NST input current (excluding my vacuum motor), and it's
pegging a 20 Amp meter, and tripping a 20 Amp breaker after about a minute
of run time. This with just one 15/60 NST! I'm trying to find or build an
AC meter to monitor the NST secondary current, this may ultimately explain
my hot resistors.
Regards, Gary Lau
Waltham, MA USA