Hi Jay,The internal construction of the PFC cap is not optimized to minimize inductance. Also, the long Frankenstein insulator(s) also add significant inductance. The equivalent series inductance (ESL) of a PFC cap might be as much as 10-20 times that of a typical Maxwell pulse capacitor (typically 15-50 nH), or 500 nH - 1 uH worst case.
However, for TC use, the PFC cap's ESL is still a very small fraction of the combined inductance of the primary circuit wiring, spark gap, and primary winding in medium/large TC - of the order of 100-200 times the inductance of the PFC cap.
The ESL of either a PFC or Maxwell pulse tank cap is basically irrelevant when used in a TC primary circuit.
Bert jhowson4 wrote:
Bert, Any idea what ESL range these PFC caps have? And how that compares to a nice Maxwell pulse cap? -Jay ------ Original message------From: Bert HickmanDate: Thu, May 18, 2017 12:30 PMTo: Tesla Coil Mailing List;Cc: Subject:Re: [TCML] Utility PFC Caps Hi David,Your plan sounds excellent. As Terry mentioned, you really don't want to tear into these caps. I've also been there, done that, while autopsying a failed/ruptured 175 pound GE pulse cap. NEVER again - what a MESS... :^/Even worse, unlike castor oil or mineral oil, many of the low-flammability dielectric fluids that GE (and others) used were really nasty, foul-smelling solvents. When the cap failed, the leaking fluid literally "ate" the backing off the indoor-outdoor carpeting below.Your two caps in series should work great just as they are, while increasing the bang size a bit. A little tweak on tuning and ballasting and they work great. And, they should be virtually bullet-proof.Play safely and make big sparks,BertDavid Rieben wrote:> Hi Bert, (and Terry O),>> Thanks for your response(s), as this list seems almost DOA these days.>> Yes, Terry I recall you mentioning to me years ago about your experience with these types of caps. As a matter of fact, you are the only person that I can recall talking with who had actual experience using these as a TC tank cap and I also recall your mentioning having to tear the case open and rearranging the internal capacitor segments from a parallel to a series orientation. (I) would really prefer to avoid that part, though! ;-)>> Actually Bert, I have located a couple of single eared, GE, 13.8 kVAC rated PFC caps (110 kV biL), that were actually stamped with their rated capacitance as 0.25 uFd and strangely enough don't have their actual kVAR rating stamped on the "kVAR" segment of the nameplate. The math would work out to ~25 kVAR, I would assume. It appears they were manufactured in the mid-1990's, and the nameplate states that the 'dielektrol IV' impregnant fluid has "less than 1 PPM of PCB", so PCBs are likely not an issue. I was thinking of the possibility of seriesing them through their bushing connections, allowing their outer casing to 'float' as the midpoint for a .125 uFd @ 27.6 kVAC rated unit, as I am searching for a cap (or cap combo) that comes reasonably close to the 0.1 uFd that I am currently using in my big coil, which is driven by a 14,400 volt pole pig. So it appears that that aside from the ferromagnetic properties of the outer metal casing (which can cause notable heating above a> mbient temp due to interaction with the generated RF magnetic fields), these would make for a good tank cap.>> Thanks for your expertise,> David>> Sent from my iPhone> _______________________________________________> Tesla mailing list> Tesla@xxxxxxxxxx> http://www.pupman.com/mailman/listinfo/tesla>>>_______________________________________________Tesla mailing listTesla@pupman.comhttp://www.pupman.com/mailman/listinfo/tesla _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla