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RE: [TCML] MMC building - some questions

Sorry, I should have mentioned to all that I am using a 6000V nst. 

Anyway, I'll do 2 strings of 16 caps as per DC's instructions

Thanks to all - 19 days to the Cambridge UK Teslathon now!

- Thomas

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: 05 October 2008 18:32
To: Tesla Coil Mailing List
Subject: Re: [TCML] MMC building - some questions

Hi Thomas,

I don't see a reason why you couldn't do this if it's just one or two 
caps at the ends. You must however consider the voltage division in the 
series string.

Say you use 11 of the .15uF 942C series caps. As you know, Ct = .0136uF.
Also say you have 10000Vp across the string, then ideally you have 909V 
across each cap as Vc=Ct/C x Vt.

Now parallel parallel cap with #11. You still have 11 caps in series 
with the last cap pair having a value of 0.3uF.

Ct ends up at 0.0143uF.
The voltage across the first 10 caps in the string increases to 953V and 
the voltage at the paired caps is 476V.

Should be ok from a voltage standpoint, but it's important to evaluate 
the voltages seen across each cap.

V1=Ct/C1 x Vt,..... V2=Ct/C2 x Vt, .... etc...

However, don't put too few of caps in series. 11 caps isn't much and may 
put a decent voltage stress across each cap. Also, the voltage seen 
across the remaining non-paired caps increases significantly with fewer 
caps in a string. Hopefully, your using a low peak voltage as in the 

Trying to tweak capacitance can be difficult compared to simply 
adjusting the primary inductance. The slight difference in C with a coil 
isn't important. It's easier to ball park the needed capacitance and 
adjust the primary.

Take care,

Thomas Ryckmans wrote:
> Hello,
> I am now building my MMC. From previous JavaTC calculation, I need about
> 0.013 uF to reach resonance. Since I am using CDE capacitors 
> 942C20P15K-F (2000Vdc 0.15 uF) I would need a single string of 11 caps to
> reach 0.013 uF and have a (recommended) voltage rating of 22kV.
> Since 1/Ctotal =1/C1+1/C2+... 1/C11 I have 
> 1/Ctotal = 11/Cn = 0.0136 uF
> The question is: can I put ONE extra cap in parallel with another within
> string to tweak the total capacitance if needed? In effect, one cap in the
> string becomes a larger cap, with twice the value at 0.3 uF
> 1/Ctotal = 1/C1+1/C2+. 1/C11 with say, C1= 0.3 uF and the others at 0.15
> Then 1/Ctotal = 0.01428 uF
> A small sketch is here:
> Could this be an easy way to tweak my tank cap value, adding caps in
> parallel to caps in the initial string to a max possible of 0.027 (which
> equivalent to two strings in parallel)
> Many thanks
> Thomas
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