Re: Best cap size for a sync gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org> 

On Thu, 29 Apr 2004 16:49:38 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> I doubt that the nature of 
>the load is significant, as the charging is done before the gap fires and 
>the load is connected.
>
>I think the issue may be that the "recommended" value may have been 
>derived from simulations which do not take into account the non-linear 
>behavior of the NST when the volume is set to "11".

I would argue that simulations are fairly poor for any transformer 
regardless of "volume setting...."  I have yet to see any SPICE package 
correctly simulate a transformer with measured R and L components.  Case in 
point if I short (nearly) the output of a "pole transformer" model using 
the info in Terry's NST PFC Test spreadsheets, I get a primary current of 
only a few Amps (23A in my model).  When I simulate an NST whose outputs 
and inputs have been measured (except actual open load voltage), I never 
get the same short circuit current to within 30%.

I recall that the "recommended" values were arrived at empirically.  Terry 
would be able to explain in more detail, but simulations were used to "what 
if," then MMCs were used to test and tune.  The best performance seemed to 
happen at about 2.6 * Cres, which was assuming some resistive losses in an 
RC filter.  Lately the trend has been to go for 3+ * Cres, which I haven't 
seen any evidence to support other than SPICE.

I think results of the same test with the input set to 120V would be 
telling as well.  ;)

Thanks for the work, Gary!

Mark Broker
Chief Engineer, The Geek Group