# 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 example.
```
```
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,
Bart

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 the
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 uF

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 is
equivalent to two strings in parallel)

Many thanks

Thomas

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