Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 10:22 PM 4/3/2007, you wrote:
Original poster: Justin <rocketfuel@xxxxxxxxxxxxx>
Hi All,
I'm trying to figure out the right size tank capacitor bank to use with
my new potential transformers.
After much thinking and poking around on the net, I've come to the
conclusion that pole pigs, potential transformers, and any other
transformer (not just NSTs) can hit a resonant condition with the tank
cap. Please correct me if this assumption is wrong. From what I
understand today, it seems that the resonant cap value is a function of
the inductance of the HV secondary and the line frequency.
Pretty much. There's also the parasitic C of the windings, but that
is small (pico or nanofarads) in comparison to the typical tank
capacitor (tenths of microfarads)
Not sure if
the primary side inductance has an effect. It would be nice if I could
simply measure the inductance of my transformer with a meter and work it
all out on paper, but I have a hunch that a reading on a non-energized
core will be different than when current is flowing through the
transformer.
Can't use an inductance meter, but you CAN do it with a volt meter,
ammeter, and a suitable resistor. Find a textbook that describes
measuring transformer parameters (not just turns ratio, but also the
reactances) or, look here:
http://home.earthlink.net/~jimlux/hv/xfmrmeas.htm
It's a bit incomplete..
There also used to be a good page on measuring Neon Sign Transformer
Parameters out there, but I can't remember who put it up. Maybe
google will find it?
On to my "real" question. In looking over several other people's coils
online, it seems that many are running much smaller than resonant tank
caps with these larger transformers with no problems. I say smaller
than resonant as a guess based on results I've seen from JavaTC when
entering the parameters listed on these coil sites.
Is it possible to run STR rather than LTR to protect the transformer and
capacitor bank? Of course everything will still need to be matched and
tuned.
Sure.. just make sure you have a safety gap across the transformer
and cap to protect them against unforeseen resonant rise. And, if
you're substantially STR, you'll have no problems. (mind you, the
stored energy is smaller, so the sparks will be shorter...)
Thanks for any input,
Justin in Austin