Re: Peak Primary currents (was Re: MMC bleed resistors)

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

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

On Sun, 14 Mar 2004 09:40:27 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Robert Jones" <alwynj48-at-earthlink-dot-net> Hi Mark,
>
>  > Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
>  >
>  > Actually, if there are more strings of MMCs and the same overall
>  > capacitance is maintained then the current is shared more or less equally
>  > amongst the strings.  So two strings will have half the current of a
>single
>  > string.
>
>Assuming the charging voltage remains fixed (and frequency) as you increase
>the number of strings you increase the number of caps per string to maintain
>a given total capacitance..
>Which is just a round about way of saying the charge voltage across each cap
>is reduced.

Absolutely.


>If  for some reason small TCs are generally designed with a low charge
>voltage across each cap then your statement is true.
>
>I think a better statement for you to have made would have been the caps are
>usable if used in a low frequency system (big secondary and or  more turns
>than general) and or only charge them to a low voltage compared to their max
>rating. This would avoid perpetuating the myth that small coils or adding
>extra strings ( fixed caps per string) decrease the peak cap current. ie its
>a voltage and frequency.

I did explicitly state that the MMC's "overall capacitance is maintained," 
meaning more capacitors per string are required to maintain the value when 
more strings are added.  Therefore I guess I don't think either of our two 
statements is "more correct" than the other, just different ways of 
explaining the same thing by looking at different aspects (overall in my 
case, individual in yours).


>When I tried to design an geek cap MMC for a small coils( 8in x 1.25in) I
>had have only 200v across the geek cap to keep the peak current within spec
>else it would have been 5000A.

Ouch!  Are there better alternatives out there for MMCs for super-high 
frequency TC capacitors than standard PP caps?


Best regards,

Mark Broker
Chief Engineer, The Geek Group