Re: Questions??

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "resonance" <resonance@xxxxxxxxxxxx>

I ran your data through a computer program and I think I spotted your 
problem --- you don't have enough turns on your primary coil to hit 
the resonace point to match the resonant frequency of your secondary 
system.  I would suggest making up a "scrap wire" primary, flat 
spiral, of 20 turns of standard #12 AWG house wire scraping a bare 
point as each turn comes around --- stagger these slightly so your 
primary tap will fit on without shorting to an adjacent turn.

You can calculate your length of wire on your sec. coil with good old 
high school math.  First, go to your local library and pick up a 
current copy of the ARRL Radio Amateur's Handbook.  They have wire 
tables that will tell you the dia. of your wire and the number of 
turns per inch.  Or, just take a piece of wire into your high school 
machine shop and ask a teacher to measure it's diameter for you with 
a micrometer (mike for short).

Circumference of a circle = pi * dia.   This gives you the length of 
wire for one turn on your sec. coil.  In the case of #26 AWG wire, 
the wire dia. is .0159 inches (159 mils), and with some slightly 
spacing in winding, this gives you 58 turns per inch.  You calculate 
the length of one turn, then multiply x 58 turns per inch, then 
multiply this by your 10 inch coil length.  Divide by 12 in/ft and 
you get approx 425 feet of wire on your sec. coil.

With 425 ft., your sec. operating resonant freq is 513 kHz for this 
coil with your pie-pan capacitance on top.  (I estimated the topload 
at 12 pF). If you have a high school electronics shop they probably 
have a multimeter than can accurately measured the capacitance of 
this pie-pan topload for you.

With your .0075 uF primary capacitance, you need 9.4 turns of primary 
coil to resonate your system.  With the 8 turns you have now --- it 
won't hit resonance point of the secondary coil.

I would suggest going to a full 18 turns and then tapping out one 
turn at a time from 5 turns until you hit the resonace point --- it 
should be around 9 or 10 turns but may be more.  The scrap wire 
primary uses 12 ga. scrap house wiring (PVC covered) and you can just 
use some slices of cardboard on edge --- make slits in the cardboard 
(4-5 pcs) to hold the wire -- to hold your temporary primary in place.

Stick a short 6 inch long wire off your pie-pans to allow the spark 
to jump into free air so you can see it's length.  Best to let it 
jump to a ground stand you can slowly back off as it gets 
longer.  Run your variac up to only 40-50% while you are doing this 
tuning and always unplug the unit before you touch the primary 
coil.  When you find the tap point for the best spark length then you 
can bring it up to full power.

Your should get 7-8 inch long sparks with this coil.

Later, if you want to improve your performance with this capacitor 
and transformer, you should use a 4 inch dia. coilform, closewound 
with #30 AWG wire.  The larger inductance (which increases as the 
square of the radius of the coil and also as the square of the number 
of turns on the coil) will increase your voltage output 
substantially.  The squaring factor is important to achieve high 
inductance ---- use large dia. coilforms.

The equation is  Vout = -L x dI/dt    inductance x the rate change of 
current (I) with respect to time.  Your spark gap controls the time 
factor, the current I is determined by your capacitor and sparkgap, 
so your best variable is L.  To increase the inductance (L) you use a 
much larger dia. sec coil.

Have fun!

Dr. Resonance