[TCML] Subject: Overheated Secondary

[bartb]

Hi David,

I think John's latest is 1.7*sqrt(input watts). I think it started out 
at something like 1.42 as the factor? John's done a number of tests 
since then including bps testing and he posted some variations to the 
equation. I think the 1.7 factor has been out there a while now as the 
number to shoot for but may be hard to achieve depending on losses. In 
Javatc I also show John's value but I incorporate a k factor depending 
on secondary diameter from which I got from Dr. R. For coils less than 
10" diameter, I'll multiply by 0.85 as an efficiency factor.

John also tested the above at 120bps. In John's testing, he lost some 
spark length with increased bps. However, that can be true in cases but 
not true in all cases. Depends a little on several factors. Actually, I 
worked this equation out several years ago. A lot more could be looked 
into, but the gap efficiency will vary for each coil which makes going 
any further a mindless ordeal.

Don't be surprised I'm running an NST in STR mode. I still believe LTR 
is safer for NST's, but it also means more dollars! I'm no different 
than anyone else (I get away with what I can when I can). But also note 
I lowered the NST voltage. Remember the static gap is self limiting as 
based on the gap width and it's own ability. So the voltage is clamped 
by the static gap and the Terry filter (with safety gap) also provides 
needed protection. BTW, this is that same coil I've ran for 30 minutes 
non-stopped. There is no resonant rise as I'm far off to the left of 
resonance. Now if I had a gap problem (stopped firing for whatever 
reason), that's when things could turn ballistic (but that's why we have 
safety gaps). Without the safety gap and with a main gap that stopped 
firing, the NST would certainly pop!

Take care,
Bart

David Rieben wrote:
> Bart,
>
> Ok, it doesn't affect the spark length as much
> as I thought it would, though. I didn't realize
> that the math worked out like this either. I was
> just assuming that the spark length was a simple
> result of the sqrt(power) x 1.2  and the power was simply a factor of 
> the bps x C, in joules. I
> guess that's what I get for assuming ;^) Also, I
> am a little surprised that you are actually running
> an NST coil STR, considering the prevailing
> school of thought about LTR operation for the
> fragile NSTs in the last decade.
> Spark on,
> David Rieben