RE: I need help!!!

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Chris,

I would start to worry about running a 15/120 system in five rows of
68nF/1600V caps.  You are getting near the safe limit for RMS current.
Hard to say without knowing the exact type of caps?  But I think they are
only good to 4 amps RMS each row.  That gives 20 amps RMS total.

There is a program that all the MMC calculations are based on.  I guess it
has sort of been forgotten now days with the tables, but it "made" those
tables.

http://hot-streamer-dot-com/TeslaCoils/programs/Mmccalc2.zip

Just simple open source free DOS based program that runs some critical
numbers for you.

Also, data like this is used when "things get close":

http://www.pupman-dot-com/listarchives/2000/May/msg00529.html

Resonant systems run at about 200BPS which also places more stress on the
caps.  RMS current is directly proportional to the BPS rate.  This is why
very high BPS systems tend to have dramatic cap explosions.

So I ran the program for your caps guessing a dissipation factor of "40"
(trust me, since I am good at this :-))):

MMC Calculator  Ver. 2.2   9/12/2000  Terry Fritz
Transformer voltage =  15000 
Transformer current =  .12 
Firing voltage =  21213.15 
Fo =  250000 
Break rate =  200 
Thermal dissipation constant =  40 
Individual cap value =  6.800001E-08 
 
Strings  Caps/Str  Capacitance  Voltage   Temp C    Cost              I Arms
  3        8         25.50        12800    20.13   24.00  :-((  :-((  14.59 
  4       11         24.73        17600    10.65   44.00  :-|   :-|   14.14 
  5       13         26.15        20800     7.62   65.00  :-|   :-)   14.96 
  5       14         24.29        22400     6.57   70.00  :-))  :-)   13.89 
--------------------------------------------------------------------
  6       16         25.50        25600     5.03   96.00  :-))  :-)   14.59 
  6       17         24.00        27200     4.46  102.00  :-))  :-))  13.73 
  7       19         25.05        30400     3.57  133.00  :-))  :-))  14.33 
  7       20         23.80        32000     3.22  140.00  :-))  :-))  13.61 

So I guess the RMS current is only about 14 amps RMS and the program says
your on the high side of fine :-))  Not too much to worry about, but I
thought I should show that there really is some science behind MMC design.
Perhaps it is getting to be a little forgotten these days when it all seems
so easy :-))  However, I was not "always" easy....

Cheers,

	Terry



At 11:26 AM 7/28/2002 +1200, you wrote:
>Hi Steve
>
>Sorry no caps but I'm doing an MMC for the same 2 x 15/60 NST's and just
>wondering what parameters your designing to.  I'm to use 68 nF caps at
>1600 VDC rating trying for 25 nF (resonant).  So I took transformer peak
>voiltage and divided this by 1600 to get the number of series caps then
>(rounded up to 14/string) then got 5 strings to give my required
>capacitance.
>
>Is this your approach?  I'm concerned about enough saps/string to handle
>the voltage.
>
>Cheers, Chris.
>