Re: CD 942 failure tonight

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi John,

I finished the spice simulations assuming that 12/120 (60Hz) was the full
power source and you are running your SRSG at 120 pps.  The Cres for this
NST (or pair of 12/60) is 26.5 nf.  The impedance of the NST is 100Kohms
represented by an inductor of 265 heneries.  The following is the peak Vc
and firing voltage as a function of phasing:

Using your 66.7nf Cp

Phase  |  Vc_pk  |  Vfire
---------------------------------
at pk     |  17.5kv |  17.5kv
+.5ms  |  20.0kv |  19.5kv
+1.0     |  22.5kv |  22.0kv
+1.5     |  26.0kv |  23.0kv
+1.6     |  27.0kv |  23.2kv
+1.7     |  28.0kv |  23.5kv
+1.8     |  27.0kv |  23.1kv

Using 83.2 nf  Cp (3.14*Cres)

Phase  |  Vc_pk  |  Vfire
---------------------------------
at pk     |  14.0kv |  14.0kv
+.5ms  |  15.0kv |  14.9kv
+1.0     |  17.0kv |  16.3kv
+1.5     |  18.2kv |  16.3kv
+1.6     |  18.3kv |  16.2kv
+1.8     |  18.3kv |  16.0kv

Please note that if the safety gap is set incorrectly and with the 66.7nf
Cp, you could expect to have 28KV on your cap.  With the larger Cp, the
maximum voltage is almost the rating of the NST.

Take care,
Gerry R


 > Original poster: "John Richardson" <jprich-at-up-dot-net>
 >
 > It's a 12/120.  I bought two new ones off of e-Bay for $15.00 apiece, and
 > after posting this guy to the list, I think Harold Weiss bought several
 > also.  With regards to the strings being hooked up, the end of each string
 > is screwed into 6" pieces of brass bar stock.  SRSG safety is at .5"
 > exactly.  NST safety is actually under .5" total.  Center of NST safety,
NST
 > case, and secondary bottom are RF grounded to Cu water pipe that runs thru
 > the basement, and then about 200 or so feet out to the well in the field.
 > When taking a video to send to Terry last night, I can see where one of
the
 > caps arced thru it's exterior to a support (Ungrounded!) over 2.5 inches
 > away.  The bottom of the cap is also split open and melted about 2/3 of
the
 > cap length, and there is positively no place in my system that this could
 > have arced to.  One of the other caps I sent Terry has zero soot and black
 > goop, just a nice clean bubble where the foil is becoming visible.  This
 > bubble is facing towards the next string over, and there is no sign of it
 > arcing at all.   Every cap and resistor in the bank is first crimped to
 > uninsulated wire terminals, and then soldered for good measure.  The are
 > attached to each other with 8/32 machine screws thru holes in fiberglass
 > electrical project board.  Each string is 9 long, and there are 4 of them.
 > This should be about .0692.  They are the 942s rated at .15 apiece.  It
 > should also be noted that all of these failed caps were located at the end
 > of the string, not in the middle.  These failures were also all on the
side
 > of the cap bank that is connected to one side of the SRSG, not on the side
 > that goes to the primary.  I don't know if that matters.  It almost seems,
 > taking into consideration the hot primary wiring, that there is unusually
 > high amperage in this tank circuit (WHY?).  One other thing that I don't
 > think I mentioned is that the capacitors were getting warm, not hot, but
 > warm.  This was on the final run which was certainly under a minute.  I
 > thought that performance was actually pretty darn good for a first fire,
 > especially when I could watch it in the dark.  The small toroid and
 > smallish, poor H/D ratio secondary are the only thing holding me back from
 > 60 + inches, maybe more.  Again that is a seat of the pants assessment.
 > Can't have caps going off like rifle shots every 60 seconds, though.  I
 > won't know till I get my meters on the control panel, but is it possible
 > that this NST is a little more robust than it's rating would imply?
 >
 > Thanks,
 > John