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Re: [TCML] NST Measurements
Lau, Gary wrote:
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?
Nope.. at least not into a resistive load.
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?
If the load is a capacitor that cancels the 15-20 Henry (approximately)
equivalent series inductance of the secondary, then you can get full
current at full voltage out (and cook things as well)
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?
The NST is, for all intents and purposes, a 15kV power supply in series
with a BIG inductor (roughly 500kohm reactance at line frequency).
if you have a zero ohm load (short the output) you get 30mA at zero volts.
If you have a infinite load (open circuit) you get 15kV at 0 mA.
If you have a 500kOhm resistive load, you'll get (off the top of my
head, 0.7*15kV, at some current 15/(500+j500) (21mA?)
That's why it's a VA rating and not a Watt rating.
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