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Re: Peak Charge?



Tesla List wrote:
> 
> Original Poster: "Gregory R. Hunter" <ghunter-at-enterprise-dot-net>
> 
> Dear List,
> 
> Please settle a minor but bothersome question for me.  In an AC powered
> Tesla tank circuit, what is the peak charge felt by the capacitor?  Some on
> the list say it's 1.4 x VAC, others say it is 2.8 x VAC.  This sounds like
> a "newbie" question, but after reading the mail for many months, it seems
> that newcomers and old heads alike are not sure about this basic issue.
> 
> Greg

Greg,

Excellent question... and the answer's not simple! You're both right...
sort of. Assuming that you're NOT using a resonant charging system, the
maximum charging voltage across the capacitor terminals would be
1.44*Vrms. Let's assume that this is the point that the main gap fires. 

The capacitor's dielectric now sees a rapid polarity reversal as the
tank circuit is driven into RF oscillation. Under heavy ringing
conditions, the capacitor dielectric actually "sees" a stress of up to
2X the voltage it was charged when the gap fired, or around 2.9*Vrms.
So, the tank capacitor must be able to withstand at least 3X the RMS
voltage even though the absolute voltage is only 1.44X. 

And to make it worse, if resonant charging is used AND the main gap
misfires, the above voltage stresses can climb to levels that are 2-3X+
higher unless clamped by safety gaps...

See... I told you it wasn't simple!  :^)

-- Bert --