Low voltage coils are just as good.........;o)) was Re: NST useability (fwd)
Hi Malcom, Jim, all,
> Original Poster: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz>
> Hi all,
>"Low" voltage running is not as formidable a task as some
> seem to think it is.......
Now I just HAD to open my big mouth ;o)). While I will agree there
is a limit to how low you can go with the voltage, I WONīT agree
that low voltage coils are worse (esp. in output length) than high
voltage coils. My 8" coil is powered by a single 7500V NST,
modified to give me 1275VA. I am using a multi gap static gap,
which is uncooled and of "cheap shot" construction (as I will be
using a rotary in the end and this is only a testbed). My dual
toroid is on the small (ROC) side, yet I get 60-63" with ease,
so I donīt think (empirical proof) that a coil powered with a "low"
voltage xformer is going to perform any worse than a high voltage
coil. I know the coil can do better, itīs just a matter of adding a
larger ROC toroid and Iīd be willing to bet, that I can squeeze
68-70" from this "low" voltage setup. IF I had to set the voltage
limit, I would say not below 6kV, but simply because it is a PTA
to get the gap to function properly at lower voltages. I do run my
coil with a pretty high coupling. The (flat) priamary is located ~
4.5-5" ABOVE the lowest secondary winding. This is as high as
I can go, otherwise I get racing sparks (which I think are due
soley to overvoltage and NOT due to static charge build up).
>From some 3500 Pupman posts I have filed away, I have taken
two guys (I hope you donīt mind) that are getting similar results
with high voltage xformers. Letīs have a closer look at these:
(My coil: 7500V/67nFMMC ---> Joules=3.76J)
Michael Tucknott (P.S: I SAW that Camaro joke on your website ;o[ )
(snipped from a post):
>When we ran the same coil with Steves pole pig and a 0.0151 ufd plate
>cap and got 46" output, but now with the MMC we got 65"-68" output
>(this is as much as the RQ gap can handle)
I believe this is a 16kV pole pig, so the primary Joules are = 3.87J
(snipped from a post):
>But the MYSTERY to me, is why I can get 49" sparks, with just 2 or
>three streamers, using just my 4" by 13" toroid, at 120 bps, at just
>950 watts, on my larger TC. Whereas others are getting multiple
>streamers with shorter sparks.
...... I think Johnīs coil is doing a little better now (58"??), but I
canīt seem to find the post in my archives (no wonder with some
3500 posts ;o})
>(2) 7200 volt, 1.5kVA potential Xfrmers in series, for 14.4kV.
>Inductive ballast, about 7mH, (set for resonant charging).
> Power input is 950 watts (wallplug).
This means Johnīs coil is running with 3.05J in the primary circuit.
John is getting a slightly better output, but then again he is
running in resonant charging modus (I am not) AND he is running
a sync RSG (mine still isnīt finished). I am sure these two factors
are giving him improved overall performance. If I now punch in the
numbers into Johnīs equation of:
Max. spark length (inches) = 1.9*SQRT input power
I get a 67" for my low voltage coil and 58" for Johnīs coil, which
pretty much match the empirical results for BOTH high (Johnīs)
and low (mine) voltage coils. If I further compare results to the
big dawgs like Bill Wysock, the results are pretty much the
same (I mean the smaller coils (~2kVA), of course).
While I WILL agree that high voltage driven coils are more forgiving of
sub optimal design and are not as finicky, I WONīT agree that they
are worse from the output spark length. They just need to be
constructed slightly different and with more care, but they DONīT
perform less spectacular!!
Coiler greets from Germany,