Re: term understanding: voltage reversal.

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Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 08:06 AM 2/18/2004 -0700, you wrote:
>Original poster: "Christoph Bohr" <cb-at-luebke-lands.de>
>Hello All.
>
>I came  across something I am no longer sure I understood that right:
>
>In pulse cap data sheets there is usually a point called "voltage reversal".
>To say it less technical I understand that voltage reversal causes stress on
>the cap and is undesireable if you like longelivity.
>But what exactly is this voltage revesal in a AC, sync gap, TC? is it:
>
>1.: The changing polarity of the carging current, i.e. the fact that I once
>carge the cap with the one polarity and during the next half sine wave to
>the other
>
>or
>
>2.: The changing polarity during the HF-"ringing". As the changes happen
>more often and more rapidly here I feel that this is the main voltage
>reversal relatet Stress on the cap.

It is the latter... the ringing of RF 
waveform.  http://home.earthlink-dot-net/~jimlux/hv/caplife.htm has some 
equations from Maxwell Labs on how to scale it.  (and how to convert Q to 
VR...)  For what it's worth, the usual TC probably has a loaded Q of 5-10.

By the way, when you run the primary without a secondary, the Q is quite 
high, and that may be why this kind of operating is notorious for being a 
"cap-killer".

For what it's worth, reversal is hard on a cap, but higher voltage is 
harder.  The exponent on voltage is much, much higher than that for the 
reversal.