Re: 8 inch coil at 100 amps

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 12/17/00 8:43:40 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:

John Freau wrote:

<< Basically the coil must be tall enough for the power input.  For instance
 Richard Hull used a 45" tall coil for 10kW or so, at about 500 bps.  If 
 your bps is lower and the bang size larger, the coil may need to be
 taller than that.  I'm guessing that your coil is shorter than 45" esp if
 you're using a high bps.  >>

Hi John, Dave Wightman,

My "Medusa" Tesla system runs up to the 10 kVA range and the secondary
is 12" dia. by only 38" long. I run appr. 300 bps and with an 8" X 33" toroid
(~35 pF), it easily produces 10 ft sparks . I now don't have any trouble with 
the secondary flashing over. However, I had to substantially reduce the initi-
al pri/sec coupling to keep it from doing this. Before I loosened the 
coupling,
I had sec turn/turn flashover problems, usually about 3 to 4" above the bottom
secondary winding. I ended up removing the bottom 15 to 20 turns from the
sec which, in effect, raised the secondary higher, in relation to the primary.
I ended up with the bottom sec windind about 2 1/2" above the innermost
primary turn. I get sparks consistantly in the 8 to 10 ft range with the 
power 
control set in the 7 to 8 kVA range with the coupling this loose.

<< I would chose
< a wire thickness that gives 1600 turns on the secondary.  This will 
< give nice low gap losses, and make the coil efficient overall.  A wide 
< coil is good too because it increases the inductance and makes the
< frequency lower (helps the gap de-ionize and quench) and it makes
< the inductance higher, which results in a higher primary surge Z
< which reduces gap losses. >>

BTW, my "Medusa" secondary is only ~ 660 turns of close-wound # 16
magnet wire and my rotory gap is twin rotory lexan disc on each end of
a double shafted motor, so I end up with 4 spark points in my RSG. My
rotory electrodes are only 3/8" X 2" long threaded brass rods and there
are 6 on each of the two disc. They are set in the discs so that one elec. in
each disc pass between the 4 stationary electrodes at the same moment.
The stationary electrodes are 1/2" X 4" long threaded brass rods, each
affixed with (3)  2" X 2" X 1/8" thick aluminum squares to help with heat
dissipation. The rotory electrodes don't get hot to the touch as they are 
cooled by the natural air flow. There is some erosion of the stationary elc-
trodes after extended use, though, and they do get quite hot to the touch 
after running for a while at high power. However, the alum. heat sink plates
keep the temp. low enough that they do not sizzle when touched with a wet
finger.

The primary cap is 83 nFD and the primary coil is 6.5 turns of 5/8" copper
tubing in Archemidian spiral with a slight (10 deg) upslope (~ 32 uH). This 
would make my bang size around 10 J/ bang. I have noticed that if I turn the
motor speed down to low that the RSG will start to double fire with each pre-
sentation, just like John mentioned. With my cap being smaller than resonant
for the 10 kVA, 14400 volt pig and the cross section of the electrodes being
as large as they are, this is to be expected.

Keeping 'em Sparking,
David Rieben