Re: troubleshooting tesla coil, continued (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 14 Sep 2007 12:52:21 +0000
From: David Rieben <drieben@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Cc: drieben@xxxxxxxxxxx
Subject: Re: troubleshooting tesla coil, continued (fwd)

Hi Marko,

The first thing that immediately sticks out to me is that your
primary capacitor is WAY too small! That much is obvious
from viewing the picture of your setup. 7 pFd is a very small
capacitance and higher values than this are likely experienced 
accidently from  the surface area of conductive objects. There's
probably just about that much capacitance in the connective
wiring of your circuit. If you apply the math, E = .5 x C x V*2, 
and assume the pk voltage of a 12 kV sine wave at 16.9 kV 
(12 kV x 1.41), you will see that you would only be firing about 
.001 Joules per bang. However, your JavaTC plots a .007 uFd, 
which is in fact 700 pFd, not 7 pFd, and 700 pFd would trans-
late to .1 Joules and this would definitely get you closer to making
sparks although it would still be smaller than resonant to the mains
60 Hz frequency. With a staitc gap, .02 uFd (2000 pFd) would be
the target capacitance area that you should be looking at to make
your capacitor larger than resonant (LTR) with your transformer
and this would further increase your "bang" energy to about .3 J.
As long as the transformer is big enough to completely charge the 
capacitor in between each bang, a bigger capacitor means a bigger 
spark.You should consider the CD 942 series MMC capacitor route, 
as they have proven theirselves to be quite durable in Tesla coil service 
and tend to end up much less bulky and more reliable than their equi-
valent "homemade" capacitor couterparts. A lot less work, too.

Once you've addressed the capacitor issue, you will almost certainly
see an improvement in your coil's performance but you will probably
be able to get even more performance by improving your spark gap 
design. I'll leave it at that for now though as your capacitor issue is
the first thing that you must address to get your coil to sparking ;^)


David Rieben

-------------- Original message -------------- 
From: "Tesla list" <tesla@xxxxxxxxxx> 

> 
> ---------- Forwarded message ---------- 
> Date: Thu, 13 Sep 2007 19:19:45 -0400 
> From: Marko Ruban 
> To: Tesla list 
> Subject: troubleshooting tesla coil, continued 
> 
> Hello guys, I'm back from a long summer vacation. As per previous 
> suggestions I have acquired an old NST transformer (12kV, 60Hz, 60mA 
> output). And the spark gap does run now with capacitor/primary in 
> circuit. However, there's no visible effect on the topload, still. 
> Could it be that badly un-tuned? 
> 
> Please see the photo of my simple setup and make any suggestions... 
> http://marko.dppl.com/TC_setup.jpg 
> 
> The flat rectangular thing in front, is the capacitor, which should be 
> about 7pF. Can't make a more specific measurement since my new 
> multimeter is still in the mail. Spark gap is on top of the NST, and 
> consists of two screws facing each other (about 0.2" adjustable 
> spacing). Wire running in the back to the right is the ground. 
> 
> Also, here's a dump of JavaTC for my coil... 
> http://marko.dppl.com/coil.txt 
> 
> Thanks in advance for any assistance. 
> 
> 
>