Terry, Re: Protecting NST's

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

Original poster: "jpeakall by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jpeakall-at-mcn-dot-org>

Terry,


>The super killer of NSTs is using a resonant size primary cap and not have
>the safety gap set right or not using a safety gap at all.  If the main gap
>does not fire for any reason, the voltage will skyrocket to maybe 80kV!!
>That will easily blow the NST as has been demonstrated 1000 of times...

Thanks for the advice. I have to admit that I don't know exactly what a
"resonant size primary cap" is. 

>
>2.  Effective filters will prevent RF from getting back into the NST's high
>voltage windings where it may do damage.  A filter circuit that I
>particularly like that also has safety gaps and even solid state over
>voltage protectors right across the NST is at:
>

And is this all the filters I should require? Nice looking job, BTW.

>
>3.  Put a fast blow fuse on the NST input.  When really large LTR cap
>values are used, there is a very odd condition where the NST looses it's
>ability to limit current.  This is believed to be due to the shunts in the
>NST saturating and no longer being able to control current.  The output
>current and voltage suddenly go to very high levels and the NST hums like
>mad.  A fuse on the input will remove power if the NST starts to draw too
>much current and stop this dangerous condition.  My small coil is very
>close to this point.  I have tried to use this effect to get super powers
>out of an NST "SLTR operation" but it just gets to scarry ;-))
>

What value should I use on the fuse?
>
>It should fire "every" time the voltage gets too high!  Once the coil is
>all happily tuned it will fire much less and maybe not at all.  Don't go
>messing with the safety to stop it from firing or the NST may very easily
>get blown.

I'm still trying to get a handle on how much is too much. So far I have
played with the primary coil tuning, (I haven't played with topload, tank
cap value or gap settings) and it doesn't seem to help. In fact, where I get
the most backfire seems to be when the primary is adjusted for maximum spark
length. But is every second or two too often? I'm leery of blowing my
sweet/cheap/in perfect shape NST!

Thanks for all the help. It would take years of experimenting to learn what
I have learned in the last three weeks.

Jonathan Peakall