Re: nonresonant cap = imcomplete charge ?

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Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <biomed-at-miseri.winnipeg.mb.ca>


Hello,

I partially disagree your statement.  The capacitive reactance of the tank
capacitor will cancel out some of the inductive reactance of the NST and in
resonance, all the inductive reactance.  Which causes the primary current
of the NST to increase up past the VA rating of the transformer.  The
inductive reactance in the secondary of the NST and its magnetic shunts
limit the current and  therefore VA power draw.

My system uses an unmodified NST, 12kv 60mA, 720 VA, which should give 6
amps of primary current but my system, measured with a RMS meter, pulls 13
amps or so.  Cap value is LTR 0.0212 uF.

Shaun Epp

----------------original message------------------
Larry,

An interesting thing about resonant sized caps, is that this
seems to be the only type that can cause an unmodified NST to
draw more than its rated power without using a step-up type variac.
This may not be true in all cases however.
However there's more danger of NST failure with a resonant
value cap.  More robust non-shunted types of transformers can run
successfully with resonant sized cap value.  Of course
in these cases, resonant value is determined by the external
ballast setting, rather than by the transformer characteristics.

A disadvantage of resonant operation with a typical primary
circuit ballast is that it steps up the transformer primary
voltage and can cause saturation and poor efficiency.
Ballasting the secondary for resonant systems is therefore
preferable, but is rarely done.

In general, an LTR cap in an NST system can provide a
reasonable bang size because although the voltage is lower,
the uF value is larger which compensates to a degree.

John