Re: Please Advise

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

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

Hi Emmett,

I second Gary's toroid size recommendation. I started a reply this morning 
and went through a pretty extensive evaluation, but low and behold, I got 
up to refill my coffee cup and the power went out for about 15 minutes. 
Lost the whole darn thing! And now I'm just too lazy (well, really I'm 
going to wind a helical primary in a minute).

Anyway, I was going to reply with a 6" x 20" toroid recommendation. This 
should add approx. 100kV potential at the terminal. Your new cap size of 
0.0375uF is about perfect for a static gap LTR size. Your 5 turn tap looked 
off about a turn higher than I would have expected. It may be that the 
0.25" spacing between turns is not exact for each turn. This is typical 
with primarys (in my case, it's always larger than I want). Your average 
spacing appears to be a little closer than 0.25". Kind of why it's good 
idea to give inner and outer diameter measurements (everything can be 
figured out from there). Javatc predicted the random air spark length at 57 
inches, so that seems to agree well (which I am personally pleased with).

The larger toroid should help breakout at a higher potential, but 
workmanship of course is key (smooth if possible). Any offbeat protrusions 
will reach breakout at a lower potential. It will be interesting to see if 
you actually gain any sparklength between your current toroid size and 
whatever you decide on next, or if the spark formation changes only. 
Thickness, direction, etc. Definately worth a go.

Emmett, I've really enjoyed watching your coil come along the past couple 
months. It's a good coil!

Keep up the great work!

Take care,
Bart

Tesla list wrote:

>Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
>Hi Emmett:
>
>Are your caps really rated for 2600V each?  If so, your cap looks great,
>I just haven't seen a voltage rating that high.
>
>I agree that you could do with a significantly larger toroid.  Assuming
>everything else in your coil is good, you probably could do with at
>least a 6" x 24" or 30" toroid.  If you ask me how I know, the best I
>can say is it's a gut feel based on my experience.  Sadly there is no
>known formula for calculating the optimal top load size, and the right
>size can make a world of difference.  Generally, performance improves as
>the top load size is increased, up to the point where it will no longer
>break out without a breakout point.
>
>Increasing your top load size will also allow you to use more turns on
>your primary, resulting in lower losses in the gap.
>
>A 3/8" total gap for a 12kV power supply may be pushing things a bit.
>I'd recommend checking that with just the NST hooked up, that the gap is
>on the verge of breaking down.
>
>Regards, Gary Lau
>MA, USA
>
>
>Original poster: "Emmett Secrest" <secrest2032-at-msn-dot-com>
>
>First let me say Happy New Year to everyone on the list. I added a
>second
>NST and additional caps to my coil tonight. I had to decrease the tap
>point
>from the 7th turn to the 5th for estimated best performance. I am
>getting
>roughly 5' streamers with frequent strikes to the strike rail. I had one
>
>primary hit but it didn't cause any damage.  I repositioned my strike
>rail
>and did not get any further strikes to the primary. I have not changed
>my
>coupling or Toroid. I get multiple streamers of 4 to 5 feet and in quick
>
>succession. My question is whether I should increase the size of the
>Toroid?  I presently have one  that is d=4 D=16.  Please correct me if I
>am
>wrong but it seems I read that if there are lots of streamers being
>produced it means the breakout voltage required for the Toroid is small
>compared to the amount of voltage being delivered. If this is the case,
>then wouldn't a larger Toroid have a higher breakout voltage point and
>then
>for a given voltage supply produce less numbers of streamers that are
>longer?  I was considering making a d=6 by D=16 Toroid.  Any suggestions
>as
>to a better size would be appreciated.  These are the spec's on my coil:
>
>(2) 12/60 NST's
>(2) strings of eight .15 uF LTR 2600v MMC's
>RQ Gap w/ fan ( 3 gaps of 1/8" each)
>15 turn primary of .25" cu tubing w/ .25" spacing between turns
>4.5 dia. secondary  22.5" winding length/ 22 AWG
>pri. even with bottom of sec winding
>2.5 spacing between pri. and sec.
>bottom of Toroid 1" above top winding of sec.
>
>Thanks for your help.  It is due to everyone's kind assistance that I
>have
>successfully built my first coil and I am sure that with your help I
>will
>get the bugs out of my recent upgrade.
>
>
>Emmett
>
>
>
>