Re: Protecting NST's

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Jonathan,

At 12:00 PM 4/22/2001 -0700, you wrote:
>Howday All,
>
>I got a 15kv/60ma NST yesterday for $20, along with 20' of HV wire. Sweet!
>(saw the NST tested too!) I hear so much about blown NSTs, and I don't wanna
>blow mine. So, aside from a safety gap, what can I do to protect my NST?

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...

I recommend three things that should make your NST practically kill proof.

1.  Always use a safety gap at all times that is properly set and never go
messing with it.  It will save the NST 90% of the time!

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:

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg

The filters on my coils are shown at:
http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/BigCoil.htm
http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/protection.jpg
http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/SmallCoil.htm
http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/small_protection.jpg

DigiKey sells all the parts.  www.digikey-dot-com  

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 ;-))

>
>I hooked up the NST to my coil (a very small one) and have applied about 70%
>power from my variac. I seem to get a fair amount of "backfire" from the
>safety. How frequently is it ok for this to fire?

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.

>
>Will the NST require substantially different tuning or SG settings? I have
>been using an OBIT up until now.

The primary cap size may have to go down.  That depends on many things.
Many programs to adjust tuning are around so you can consult those.

Cheers,

	Terry


>
>Thanks all
>
>Jonathan Peakall
>