Re: nonresonant cap = imcomplete charge ?

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 10/23/02 1:34:50 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:



>
> 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



Shaun,

I assume you are not overvolting the NST past 120 Volts input?
I assume too that you have not depotted the NST or changed it in
any way?

Well in any case, I said that what I said below may not be true
in every case....

John


>
> ----------------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
>
>