Re: Please Advise

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

Original poster: "Emmett Secrest" <secrest2032-at-msn-dot-com> 

Bart...thanks for the info. Forgive me for asking for an explanation but I 
am not sure I understand what you stated about the spark gap setting.

"Probably Dan, I don't remember discussing gap distance. Have you checked
the NST with the sparkgap out of the circuit? This will identify the NST's
maximum output voltage for arcing across a given distance. Just be sure to
do the adjusting with the NST unplugged. Decrease the gap until you find
the arc distance which is steady. Then lock the distance in place and put
the system back together."

If I understood you I should find a spark gap setting where the NST fires 
continuously across the gaps and lock it in at that setting( that is 
without the cap bank or primary connected). I had previously set the safety 
gap at where it just didn.t fire with the NST powered up.

I think that rather than lower my secondary so much and thereby decrease 
the distance  between the toroid and the strike rail I will cut my primary 
and add more turns to obtain the 1" clearance you are running.. I have felt 
I should do this but had been avoiding the task. Thanks for the prod I needed.

Emmett


----- Original Message -----
From: <mailto:tesla-at-pupman-dot-com>Tesla list
To: <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
Sent: Tuesday, January 06, 2004 9:00 AM
Subject: Re: Please Advise

Original poster: Bart Anderson 
<<mailto:classi6-at-classictesla-dot-com>classi6-at-classictesla-dot-com>

Hi Emmett,

Tesla list wrote:

 >Original poster: "Emmett Secrest" 
<<mailto:secrest2032-at-msn-dot-com>secrest2032-at-msn-dot-com>
 >Bart...just to give you an update on the Toroid change.  As I said
 >previously I produced less numbers of streamers with the 6x30 Toroid and
 >they also did not appear as bright and were not as long as with the 4x21
 >Toroid.  Again tonight I had the same results. I decided to change my
 >overall spark gap setting since either you or Dan had stated I was pushing
 >it with a total of 3/8".

Probably Dan, I don't remember discussing gap distance. Have you checked
the NST with the sparkgap out of the circuit? This will identify the NST's
maximum output voltage for arcing across a given distance. Just be sure to
do the adjusting with the NST unplugged. Decrease the gap until you find
the arc distance which is steady. Then lock the distance in place and put
the system back together.

 >I changed the total gap to .165" and was surprised by the results.  It
 >required re-tuning .5 turns out from the center. It went from 4.5 turns to
 >5 and 1/6th turns for the 4x21 Toroid and 6 and 1/6th turns for the 6x30
 >Toroid. Can you explain why changing the total spark gap setting affects
 >the tuning point?

The gap distance decreased substantially and lowers the voltage at the cap
at gap conduction. I think what you've done is basically tuned for longest
sparklength at the lower voltage, and in the process of this, your slightly
detuned high on inductance (the correct direction) about 8 to 10%.

 >This is probably basic stuff for you experienced coilers but it really has
 >my curiosity peaked.  I think the 6x 30 may be a little large so I am
 >going to cut it down to 24" O.D. and give it another try.  I will also try
 >your suggestion on raising the primary via lowering the secondary. I
 >originally had it set at 2.5 inches up from the bottom winding of the
 >secondary. Honestly I had forgotten about that and it is an easy change.
 >The results should be interesting. I did receive some racing sparks on the
 >secondary with the 6x30 Toroid.

Racing sparks are caused from too much voltage stress at some point on the
secondary. Coupling and being off-tune are the two most common situtations
to cause racing sparks. With the 6 x 30, I expect you were tuned low on
inductance.

Coupling adjustments should be performed. Something to be aware of is you
have 2.5 inch clearance between secondary and primary. This is actually
quite wide compared to most. I run 1 inch myself on a similar coil. This
allows me to set the sec base about even with the inner primary turn for k
of 0.153. Coupling is a function of the proximity of the two coils. Because
of your 2.5 inch clearance, your coil will have to be lowered further than
my own to achieve the same k factor.

 >I'm not sure what I did to stop them but it hasn't happened again with the
 >large toroid. With the 4x21 and the new gap setting I am getting two to
 >three streamers at a time that are very bright, seem to be wider than
 >before and are around 4 feet in length. I am not positive on the distance
 >as I have not tried to accurately measure them.  Lets just say they are
 >nice streamers and they make me very happy.  Oh , one other question, is
 >the .165" gap acceptable or do I need to decrease it further?

One person can say "here's where I set my gap", but there are a lot of
variables which make possible a gap to arc from point A to B at a given
distance ("far" more than simply the voltage potential). Setting the gap to
the NST output is a perfectly valid "measurement". It beats hope and
guesswork any day of the week.

Take care,
Bart