Re: [TCML] NST Measurements

[Sfxneon@xxxxxxx]

Gary,
 
With a largely resistive load, like neon tubes, the NST will not  output 15 
kV -at- 30 mA. It is designed to produce 15 kV open circuit until  ignition, 
and then the voltage should drop to about 60% of the nameplate rating.  The mA 
rating on American transformers is the shorted value (ammeter directly  across 
the NST) such as 30 mA or 60 mA, but this value should drop to 80% (24 or  48 
mA) when properly loaded. 
 
15 kV x 30 mA does equal 450 VA, which is also the input VA, but only after  
power factor and losses are corrected for. The actual secondary VA rating  
would be closer to 216 VA across a resistive load.
 
So, a 15/30 NST properly loaded will output about 9000 volts at 24 mA while  
operating. I know that everything goes out the window when L and C are  added 
to the circuit, but these are the specifications that NST manufacturers  
design their transformers to. 
 
(NOTE: The recommended method of loading a NST is to measure the secondary  
operating current, and select a transformer that will produce between 77.5% and 
 82.5% it's nameplate rating.)
 
Tony Greer
______________________
 


In a message dated 1/22/2009 8:33:47 A.M. Central Standard Time,  
Gary.Lau@xxxxxx writes:

Maybe the question I really want to ask is - under what conditions will  a 
15/30 NST deliver 15kV AND 30mA?  Is that even possible?  I would  have assumed 
that with a "proper" load, Vload would be 15kV and would draw  30mA.  Could it 
be that the open circuit voltage really is supposed to be  something much 
higher but settles down to 15kV under load?  

You  mention that "30mA would drop the voltage very low ".  If that's true, 
then  we should never be able to draw anything close to the faceplate-rated 
power from  an NST.  Have you measured this?  Or does the faceplate VA rating  
reflect just what is being pulled from the wall, with much or most of that being 
 dissipated as I2R losses in the core?

Sorry for all the question marks,  but it appears that our understanding of 
NST's is not as good as we had  assumed.

Regards, Gary Lau
MA, USA
 
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