Re: Wire Guage and Q?

In a message dated 00-01-01 16:29:08 EST, you write:

<< Greetings, All!
>      I am wondering about Q and how it relates to wire guage.  My present 
> coil seems to be getting rather poor output.  I have a 15/30 NST power 
> supply (I kicked it up to 60 mA a couple times because I do have a bunch of 
> other trannies) but my dad won't let me pump more raw wattage in until I 
> out the coil at its present spec.

Nathan, all,

THere is presently some controversy on just how important the Q is,
but I doubt that the Q is what is hurting the performance of your coil.
I didn't see any mention in your post about the actual spark length
you're obtaining.
> I have a 0.005 uF cap that's polyethylene sheeting, and I just moved to a 
> rotary gap that is now synchronous at 120 BPS.  I am pretty sure it's sync 
> now that I modified it because the lights turn off when I run it until the 
> demand controller catches up.

Well it's easy enough to tell if it's in sync, just tape a white cardboard
disc onto the gap rotor, and draw a heavy black line across the diameter,
and if this line can be seen as a fuzzy line that's not rotating when the
gap is spinning, under fluorescent lighting, then it's locked and synched.
(some folks have trouble seeing this, so there are other ways to observe
it....but they're more trouble to set up.  The TC should *not* but running
during this observation.)  I don't understand what you mean by the lights
turning off on the rotary.  Do you mean it doesn't fire until a certain
point.  You say you're pretty sure it's synched now?  Does the spark
output change as you adjust the mechanical phase setting of the
rotary?  If not....then it's not synched.  Running non-sync will probably
ruin the NST.

With the size of capacitor you're using, you'll tend to get some resonant
charging, so your voltage will go quite high on the NST output and
capacitor.  I've had good results with this method in my own sync-
gap TC's (45" sparks from a 15kV, 30ma NST), but many coilers prefer
to use a larger cap to keep the voltage lower and reduce the stress on
the NST and cap.  I used 0.0073uF.  And I do use larger caps 
(0.0147uF) now in general.  With the cap size you're using, you'll
have to set the safety gaps very wide on your NST, for good spark
output.  This stresses the NST and cap.
> Anyway, straight to the point.  My secondary is on 7" dia T-600 PVC pipe 
> 24.5 inches of it are wrapped with 20 AWG wire.  Most of the coils I have 
> seen comparable to my size are wound with at least 22 guage, some even up 
 >25.  How exactly does Q come into play? I originally wrapped the secondary 
> with 20 guage because I read bigger guages get higher Q but also higher 
> isotropic capacitance.

The isotropic capacitance will be the same regardless of the wire size.
Larger wire gauges do not necessarily give a higher Q.  I did a recent
test in which I rewound my secondary which was originally #28 wire
on a 6.5" by 24" form, and originally gave 42" sparks at 570 watts.
After I rewound it with #20 wire as a test, it gave only 38" sparks.  So
I lost about 10% spark length with fewer turns of thicker wire.  So 10%
is the most you can expect to gain if you go to a thinner wire such as
#28.  It seems that the reason the #28 wire gives longer sparks is 
because of improved impedance matching to the streamer, but more
work needs to be done in this area.  Actually, because of the proximity
effect, the best Q will be obtained if the windings are spaced a little.
Aim for a winding fill factor of 50% to 75% for best Q.  (My coil is
closewound however).  But if you use thick wire and spacewind, this
will be *very* bad, because the inductance will be low and the impedance
match poor.

> My primary is 15 turns of 1/4" refrigeration tubing at a 35.5 degree angle 
> spaced 1/2".  I think my secondary operates at about 300 kHz and I thought 
> with higher Q, precise tuning is required, but I can't see much difference 
> in output between the 13th and 15th turns on the primary.

I don't think the Q will really make a noticeable effect on the tuning
precision.  Did you try reducing your coupling by raising the secondary
BTW?  Sometimes this can help a little.  You have a  pretty sharp
angle on your primary, so the secondary may need to be raised some.

Are you sure you have enough turns in your primary?  You could
try adding a piece of #12 scrap wire to the outside of your primary
to see if it helps as a test.
> If I made a new secondary with finer wire (23-25AWG) would my coil run 
> better?  I tried to run my specs through WinTesla as best I could, but you 
> have to put in your desired output voltage first in the coil designer 
> instead of putting in your own specs and the program tells you what your 
> output should be.

You most likely won't gain more than 10% longer sparks with thinner
wire, but the coil will probably run better and the gap will run cooler,
due to better impedance matching, which will improve the spark
loading and quenching.
> It told me for 200,000 V output voltage (which I think represents a foot of 
> output) with my present power supply and 15 primary turns that I needed 25 
> guage wire on the secondary.  Shoot! especially after all that work, AND 
> blowing $40 on a full 10 lb roll of 20 guage.  I may be able to trade that 
> roll and some money for a roll of 24 guage or so, but need I do this? have 
> really maxed out my specs?

Well, I'm curious how long your sparks are now?  What about a toroid?
What size is it?  I use either a 4" by 13" smooth toroid, or a 5" by 20"
dryer duct toroid.  With a larger toroid, you'll need more primary turns
to tune the coil properly.

Well, I would make sure your sync gap is really synched, that the
coil is tuned well, with large enough toroid, etc.  BTW, beware the
*many* coiling myths "out there".

Coiling for the New Millennium
John Freau
> Thanks, and Happy New Year!
> Thank goodness Y2K didn't take down our beloved discussion list!
> Nathan Ball >>