Re: Step-Up Xfrmr Question

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>




Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" < 
evp-at-pacbell-dot-net> 
clip----- 
    No mystery here at all.  The capacitive load "cancels" part or all of 
the leakage reactance built in for current limiting.   A primary with a 
so-called "matched" capacitor would be series resonant and one could 
draw current limited only by the transformer resistance; a couple of 
amps for the 12 kV 60 ma transformers I have which have about 5000 ohms 
terminal-to-terminal.   Of course, the transformer would fail due to 
insulation breakdown, even though the core would saturate.....  Things 
are quite different with spark loading of the capacitor, which reduces 
the effective Q of the secondary to a degree depending on the details of 
the spark gap.   If you get "greedy: and in the effort to get longer 
streamers widen the gap too far you get the sort of disaster reported 
here quite frequently. 

    It seems to me that the use of PFC's with a capacitor-loaded 
transformer is problematic at best and may do nothing more than help 
keep down line-to-line impulses on the primary of the transformers. 

Ed 

Hi Ed & All, 

      Sounds like you're saying that putting a PFC cap across an NST is not 
good for it, is counter-productive to current limiting, and may cause more 
trouble than it is worth. Perhaps this explains what is happening with our 
new coil. Without PFC, the voltage and current rise smoothly from 0-60V and 
0-8.2A At about 62 V input, the main gap starts to fire and the ammeter 
(Weston model 155 in oak case) needle does a random-walk over the range of 4 
to 12 A. With the PFC correction in the circuit, the voltage and current rise 
smoothly from 0-60V and 0-5.95A At about 62 V input, the ammeter needle again 
does a random-walk over the range of 4 to 12 A. Does this indicate a problem 
with the PFC, NST, or is it just me being overcautious? We are not running to 
full power indoors, as this is a basement workshop with overhead gas line. 

      The system is configured as follows: 

1)    Power Box: Inlet cable-12Amp fuse-inlet switch-12Amp EMI filter 
(backwards)-20Amp/120V Variac- 0-130V AC voltmeter, 0-25 Amp ammeter- power 
outlet switch- outlet cable. Power box components grounded to mains ground. 
2)    PFC Box (Tupperware): 6 parallel 660VAC caps, 89.6uF total- second 
cable. 

3)    "Blitzwerfer": 15/60 NST w/safety gap. Each output leg of tranny has a 
200-ohm, 200W wire-wound resistor at ~300 uHy (open porcelain tube 1.675" X 
6.5") as a poor-man's RF choke.- Aspirated spark gap (ala 
www.Altair-dot-org/projects/suckergap/) .018uF x 60Kv rolled cap, 12T .25"Cu flat 
spiral primary, 4.28" x 820T 23ga secondary w/4.25x18 toroid. Secondary is 
grounded via 40" #6 battery cable to 5/8"x48" copper-clad rod driven 42" 
through basement floor. No other HV component is grounded. Runs at 285 KHz.