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Re: 942c20p1 caps

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Stephen,
You must be looking at a chart for the 0.15uF CD caps, not the 0.1uF CD caps which you listed in the subject line. However, for a 12/60 NST, the 0.0133uF is the resonant cap size. You don't want to run at resonance with an NST, but outside of resonance to protect the NST from being overvolted due to resonant charging. If using a static gap, you'll want to be somewhere between 1.4 and 1.6 times larger than the Cres value (in my book). You can of course run larger, but I have found better performance in this range. 

0.0133uF x 1.4 = .0186uF
0.0133uF x 1.6 = .02uF.
A value of C somwhere between would be ideal.
The caps have a 2000V rating, so 11 caps would yield a cap bank value of 22000V, which is a little under twice the NST output voltage and you don't really want to go much lower. I prefer to use more caps per string myself for a bullet proof rating. Anyway, you could setup your own chart and identify how strings stack up, kind of like this: 

1 string of 11 = 22000V at .0091uF (0.684 x Cres) *too small*
2 strings of 11 = 22000V at .0182uF (1.37 x Cres) *OK, but with a little resonant charging* 
3 strings of 11 = 22000V at .0273uF (2.05 x Cres) *large*

1 string of 12 = 24000V at .0083uF (0.624 x Cres) *too small*
2 strings of 12 = 24000V at .0166uF (1.25 x Cres) *small with resonant charging* 3 strings of 12 = 24000V at .025uF (1.88 x Cres) *large, but would be ok. low bps* 

1 string of 13 = 26000V at .0077uF (0.579 x Cres) *too small*
2 strings of 13 = 26000V at .0154uF (1.16 x Cres) *small with a lot of resonant charging. NST death likely* 3 strings of 13 = 26000V at .0231uF (1.73 x Cres) *large, but would be ok. low bps* 

1 string of 14 = 28000V at .0071uF (0.534 x Cres) *too small*
2 strings of 14 = 28000V at .0142uF (1.07 x Cres) *small, NST death likely*
3 strings of 14 = 28000V at .0214uF (1.6 x Cres) *GOOD*

1 string of 15 = 30000V at .0067uF (0.504 x Cres) *too small*
2 strings of 15 = 30000V at .0134uF (1.01 x Cres) *small, NST death likely*
3 strings of 15 = 30000V at .02uF (1.5 x Cres) *GOOD*

1 string of 16 = 32000V at .0063uF (0.474 x Cres) *too small*
2 strings of 16 = 32000V at .0126uF (0.947 x Cres) *small, NST death likely*
3 strings of 16 = 32000V at .0188uF (1.41 x Cres) *GOOD, with slight resonant charging* 

1 string of 17 = 34000V at .0059uF (0.444 x Cres) *too small*
2 strings of 17 = 34000V at .0118uF (0.887 x Cres) *small, NST death likely*
3 strings of 17 = 34000V at .0176uF (1.32 x Cres) *OK, with resonant charging. NST death possible* 

1 string of 18 = 36000V at .0056uF (0.421 x Cres) *too small*
2 strings of 18 = 36000V at .0112uF (0.842 x Cres) *small, NST death likely*
3 strings of 18 = 36000V at .0168uF (1.26 x Cres) *small with resonant charging. NST death possible* 

And the candidates are:
2 strings of 11 for .0182uF = 22 caps = least expensive. Not a great voltage rating. Some resonant charging. 3 strings of 14 for .0214uF = 42 caps = good voltage rating. Keeps NST alive for a long time. 
3 strings of 15 for .02uF = 45 caps = same as above.
3 strings of 16 for .0188uF = 48 caps = good voltage rating. Some resonant charging.
I personally like the .0188uF cap size taking advantage of slight resonant charging and faster charging rates. The nearer C is to the resonant value, the higher the charging voltage is at the transformer. Too high and the NST will overvolt one of the secondary hv windings. NST's won't tollerate resonant charging well, but will work for slight resonant charging. 

Take care,
Bart




Tesla list wrote:


Original poster: "stephen costanza" <baywatch106@xxxxxxx>


I was wondering about those caps . I have a 12000 60ma transformer,
and from some MMC design chart it is telling me that I only need 1 string of 11 caps. Does this sound right? The chart says I should have a desired capacitance of .0133uf and an actual of .0136 with the 11 MMC caps. Any ideas?