Re: Cap-driven x-former?

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

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 08:41 AM 6/8/2004 -0600, you wrote:
>Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
>If the capacitor simply performs PFC, the worst that could happen was a
>factory installed powercord melt down in the absence of it. He stated than
>when removed it does not work.
>
>---Eric

The list posts are somewhat incorrect (unless the H&R is very different 
from the C&H units)... When I measured the output voltage open circuit, it 
puts out the full voltage, regardless of whether the capacitor is connected 
or not.

A bit of difference between "does not work" and "doesn't work as well as 
without the cap"...  In a TC, you're driving a pretty nonlinear and 
reactive load, and the interaction of PFC, series ballast inductance, and 
resistance with that load is difficult to predict, particularly if you're 
running a static gap, and a primary tank cap that is "close to resonant" 
with the HV transformer.

None of the reports on the various lists indicated that any systematic 
effort was made to understand the effect.  It was more: I got lower voltage 
without the cap, I was worried about arcing anyway, because I already blew 
up on transformer, it worked better without the cap than with.

I will say that using these transformers in a TC might require a bit of 
optimization, mostly because of the non-trivial interactions among the 
windings and internal and external reactances. They are neither a simple 
"pole pig/potential transformer" or a simple "current limited NST".

I will also say that they sure don't seem to behave like any of the other 
ferroresonant transformers I've seen.


IF you don't have access to a bunch of cheap NSTs AND you want higher power 
AND you don't want to hassle with a pole pig or potential transformer, 
these transformers might be just the ticket.  4 of them make a very nice 18 
kV, 200 mA current limited transfomer for about $250 ($50 each for 4 
transformers, $50 for hardware to mount them) that weighs about 150 
pounds.  I built mine on a steel handtruck/dolly in the centertap grounded 
cascade configuration with air insulation.  It has seen many hours of very 
hard use (many hours in a day) making big jacob's ladder and drawn sparks 
in a big gap without much trouble, although I haven't run a TC with it.

If you wanted to get more current, you could run the primaries in parallel, 
secondaries in series, immersing the transformers in oil, 
approach.  Heavier, messier (oil), but more power.