[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] NST Measurements



Talking about NST behavior is a bit like discussing the weather--interesting chat, but not likely to change anything.  I'm not being critical--I'm as intrigued by this topic as anyone, since I have a pretty good collection of old NSTs.

Yes, the measured short-circuit current of every (good) NST I've ever tested was very near the faceplate value.  I don't own a high voltage probe, but others have assured me the open-circuit voltage equals the faceplate value.  This is not terribly useful for determining "real" power.  15kvac X 30mA = 450VA, but I doubt the NST can really support its full potential across a load that draws 30mA.  Anybody have a high voltage probe plus a 500k, 500W, non-reactive, high-voltage resistor to test my thesis?  Me either!

Besides, I don't know how useful a true dummy load test would be for either coilers or sign makers.  a neon sign doesn't present a pure resistive load, does it?  A Tesla coil cap bank certainly doesn't.  The sign presents a negative resistance load which feels like an open at first, but almost like a short-circuit once the arc is struck.  In its proper role, the NST is really just a self-starting lamp ballast rather than a true HV power supply.  Likewise, the Tesla coil tank cap presents a dynamic, highly reactive load which rapidly swings from a short early in the charge cycle, to an open at the end.  The cap repetively dumps its load, presenting the NST with a wild bucking bronco ride, with mains resonance effects thrown in for good measure.  The NST manufacturer never imagined such an abuse of their product.

Perhaps the most useful info on real NST power is right on the data plate.  I've seen more than one 15/30 NST marked "250VA" by the manufacturer.  Given their insider knowledge, this seems like a sensible figure.  I'm no sign guy, but I bet a 15/30 NST can fire 250W of neon lamps 24/7.

So how much real power can an NST deliver to a TC tank circuit?  We can only guess until someone comes up with a way to accurately instrument it.  Until then...make some sparks!

Cheers,

Greg


--- On Thu, 1/22/09, Sfxneon@xxxxxxx <Sfxneon@xxxxxxx> wrote:

> From: Sfxneon@xxxxxxx <Sfxneon@xxxxxxx>
> Subject: Re: [TCML] NST Measurements
> To: tesla@xxxxxxxxxx
> Date: Thursday, January 22, 2009, 5:25 PM
> Exactly. The whole point of the shunts is to turn the NST
> into a current  
> regulated transformer. Unlike incandescent lamps which are
> self-ballasting  
> because they increase in resistance as the current
> increases, neon tubes  (or spark 
> gaps) DECREASE in resistance as the current increases, and
> have to  have a 
> constant current (with a floating voltage) power supply.
> The current will  
> remain essentially the same as the tubes age and require
> more voltage. Exactly  how 
> this translates into useful coiling information I'm not
> really sure, but  
> that is the design principles of an NST.
>  
> Tony Greer
> ____________



      
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla