[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: JF efficiency theory (again)
Original poster: "Ross Overstreet by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ross-o-at-mindspring-dot-com>
I better clarify. My little coil can do the occasional 6 ft arc IF indoors,
in completely still air, and running a smooth toroid. Most of my outdoor
runs can only reliably hit 5 ft. My static gap is starting to show signs of
being overpowered and I can't recommend using a similar TCBOR/RQ gap on a
coil any bigger than mine. I have no way of measuring input power to my
coil. The NST produces 200ma out at 120VAC input but I have been running it
at 140VAC lately. This measurement is also dead shorted through a meter and
will not hold for a functioning coil. My power meters bounce all over the
place but seem to average around 130V -at- 25A. Again, this doesn't tell us
much because my PF is terrible.
I believe that the design principles for small coils (say secondaries less
than 10" in diameter) and the design principles for large coils are a little
different. I'm working on a post about this but haven't gotten it together
yet. Not many hobbyists have experience with large coils. Only a handful
of serious hobbyists and Special Effects companies have built more than 1
big coil. Those that have build lots of big coils aren't talking :-)
There is no doubt that John F has figured out how to coax the longest arc
out of a medium size coil but I don't know of any sucessful big coil that
has more about 1000T. I also note that most use some sort of insulated wire
instead of magnet wire to lower the TPI and inductance/inch. I also don't
usually see large primaries on big coils - most seem to use as much capacity
as they can reliably charge and then use only the number of primary turns to
I would be interested in hearing the thoughts of any of those who have built
large coils on the best design principles.
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, February 18, 2001 12:59 PM
Subject: JF efficiency theory (again)
Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>"
First off, If you haven't done so already, read through
I was wondering why some coilers get such good results when completely
disregaurding such details. For instance, Ross Overstreet's coil:
6"x24" wound with #22 for a total of ~880 turns, a primary of approx 7-8
turns (from the photo) and ~2.2kVA input along with a static gap. He gets
6-7 ft sparks which is just about right from 1.7(sqrt(input power)).
However, he's only using half the reccommended number of turns on both the
primary AND secondary. Is it possible that it is not the NUMBER of turns,
that maybe it's simply proportionate on some level?
Also, I Find that where people follow the 1600 turn rule they, more often
than not, neglect the 24-34 primary turn suggestion. I personally don't see
how one could always use 24-34 turns and still maintain a resonant
condition. How is anyone supposed to achive such high levels of efficiency
if they must choose between resonance and high primary surge impedance? Are
we just supposed to use thin wire on the primary?
I once used two #22 wires in parallel for the primary on an early coil I
made. It worked quite well too.
If we want high primary surge impedance, why does everyone concern
themselves with using welding cable as tank wiring?
Mike Waddick and I compare notes often and he is using the 6x24 with #22 as
well. Wouldn't the optimal wire guage be as follows?:
Just trying to get more bang for my buck,