Re: tank circuit of VTTC

["Bert Hickman" <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:
> 
> Original poster: "Herwig Roscher" <herwig.roscher-at-gmx.de>
> 
> Bert Hickman wrote to the list:
> 
> > ...... Another alternative to the MMC may be a water-cooled
> commercial induction heating capacitor. 235 amps is a lot ofRF
> current... :^)
> 
> Bert,
> 
> Your answer sounds discouraging, but obviously is was *my* fault.
> The 235 A I've mentioned is *not* the RF current but the peak
> current my planned MMC could handle.
> 
> I'd like to know whether amperage (235 A peak) and voltage (40
> kVdc) of my tank cap and wire gauge (AWG 8) of my tank
> inductance are in the ball park.
> 
> Very sorry for confusion.
> 
> Regards
> 
> Herwig


Herwig,

No problem. In that case we need a bit more information to properly
answer your question:
- Planned plate voltage?

- Planned tank circuit C and L?

- Planned duty cycle (are you planning to drive from half-wave,
full-wave, or filtered DC)?

- How many strings of caps will be connected in parallel?

Assuming you're running in class C operation the peak-peak RF voltage on
your tank cap can be 2X the applied plate voltage, and the peak
circulating tank circuit current can be as much as Vplate*Sqrt(C/L).  

Once you've defined these, you can then begin to determine the
suitability of your planned MMC tank cap design. Unlike a disruptive
coil, a VTTC typically has a much higher duty cycle... as much as 100%
in the case of a system driven off a filtered DC supply. The combination
of high RF RMS currents and high duty cycle make your application a
potential capacitor killer, especially as you begin to increase plate
voltage. Flimsy leaded caps need not apply for this job... :^)

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-com
Web Site: http://www.teslamania-dot-com