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Re: [TCML] Toroid question



bartb wrote:
Hi Gary,

That is an interesting point indeed.. But I'm not so certain the claim you stated is certain. For example, I tested 0V to 150V on a 15/30 NST for various measurements. In this example, take a look at Vout, when Vin is pushed beyond the 120V measurement.
http://www.classictesla.com/temp/15-30nst-vout-vin.gif
Note that Vout begins to diminish linearly to the previous input values linearity. Also note this is open circuit Vout (nothing terrible occurred, but not a recommended measurement).

Here is a look at short circuit current through 120V up to 150V. EXTREME LINEARITY! This is telling.
http://www.classictesla.com/temp/15-30-shortcircuitcurrent.gif

And lastly, I think the coupling is really showing what happens. Note how the internal coupling with the NST peaks and decreases as V is increased, I'm sure this is matter of the leaky shunts affecting the core.
http://www.classictesla.com/temp/15-30nst-coupling.gif

All in all, I think the increase in voltage above and beyond is actually linear from a a current stand point. I agree that using NST's above their nameplate rating is common and normal. Spark gap breakdown setting is of course important and dictates NST probability of failure. If a moron opens up the gap beyond the NST's winding withstand voltage, then the darwin award is up for a grammy!

Dex is not only wrong, but obviously very new to coiling (as you know). We've been down this very path a thousand times...

Best regards,
Bart


I think it's not a coupling change, but an increase in loss as the core saturates. The VA drawn from the wall increases, but the VA out from the secondary decreases. (with the difference going into heating the core)..

I've got some measurements around on a similar transformer and it shows a definite flattening out as the vPri went above about 130V. The PF actually gets better as you go higher (because instead of looking like an inductor, it's now an inductor and a resistive heater).

I'd also note that the current waveform starts to get real funky and non sinusoidal (it gets peaks on top of the sine), so a average or rms reading meter may not be reading correctly.

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