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capacitor questions!!!

 * Original msg to: Robert.thaden-at-amd-dot-com
 * Carbons sent to: usa-tesla-at-usa-dot-net

Quoting Bob Thaden <Robert.Thaden-at-amd-dot-com>:

> I've got a question that a 20 year EE probably ought to know, 
> but I don't: The plans for my old Tesla coil provided by Morris
> and Lee include a chart used to select the right sized 
> capacitor, independent of the tank frequency. 

> It is a chart that shows the voltage attained across the HV
> transformer and capacitor (with a 15kv neon sign supply) due to
> _60Hz_ resonance.  For small variations in the capacitor size,
> we see the voltage range from 15 up to 30KV.

I edited out the chart. RQ

> According to this chart, the caps we're buying would not work 
> in my circuit, since the neon-sign secondary would surely 
> breakdown (even if the caps can take it).

Humm, in practice I have never had a problem. A decent RF choke,
safety gap, and bypass caps should prevent any damage to the cap
or power supply in the event of any problem. By varying the value
of the bypass capacitance and the inductance of the choke you
should be able to tune out any low frequency resonance between
the xfmr and the tank circuit capacitance. Those "old" books
really are out of date for the most part.

> Did anyone ever supply those requested specs (dc rating and 
> shot life)?  

The DC rating should not really be much of an issue, but these
caps are high-pot tested to around 35 kvdc and withstand
considerably more in a pinch. The shot life is great enough to
provide many years of service to the typical coiler.

> I still don't understand the '100% reversal' comment. 

Voltage reversal during oscillatory pulse discharging.

> I don't even understand the significance of the 'pulses per 
> second'. 

This is referring to the break rate, or firing rate, of the tank
circuit. This number is typically expressed in "BPS" meaning
Breaks Per Second or "PPS" which is Pulses Per Second (these
terms are interchangeable in this application). This is
essentially the number of times per second the spark gap fires.
The higher the PPS (or BPS) the harder the capacitor is working.

 > These are running at 100khz.  Does this mean you can't use a   
 > static gap? 

These capacitor will work fine with any type spark gap.

Richard Quick


... If all else fails... Throw another megavolt across it!
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