# Re: [TCML] MMC design

```Matt:

it's 30mA

Paul  (not the comfy chair!)
```
----- Original Message ----- From: <Mddeming@xxxxxxx>
```To: <tesla@xxxxxxxxxx>
Sent: Wednesday, January 16, 2008 3:01 PM
Subject: Re: [TCML] MMC design

```
```
In a message dated 1/16/08 11:00:29 A.M. Eastern Standard Time,
dunnsept@xxxxxxxxxxx writes:

I'm  going through some of the MMC calculators on the net trying to figure
this  stuff out.
I have a 9kv NST and LTR capacitance is 12.5nF
output of the  NST is ~13kv p-p   (close enough)
so, assuming 0.1 2kv caps
1  string of 8 = 16kv and 13nf
2 strings of 16 = 32kv and 13nf

is 16kv  "high enough" above the NST?
```
is it just a waste to go with 2 strings of 16, should I, in this scenario,
```stick with 1 string of 8 and call it  good?
if the caps were 0.047 and 2kv, then 2 strings of 8 = 16kv and  11.75nf
or 3 strings of 11 at 22kv and 12.82nF

which is more  important in designing the MMC?
is it more important to be as close as  possible to the LTR value or have
```
enough voltage "padding" above the xmfr? is there some other factor in here
```to use (like the discharge energy or  something?)
thanks

Paul (I didn't expect the Spanish Inquisition) in  Michigan...

_______________________________________________

Hi Paul,

There is some flexibility around the LTR value; many folks consider  20%
```
tolerance as OK. In general, longer strings = more voltage-spike protection, more strings = more current handling capability. Dr. R's suggestion will give you
```a virtually bullet-proof design from a voltage standpoint.  You didn't
```
mention the current rating of your transformer. Too few strings, and your caps will
```heat up on peak currents, too many and your cost goes way  up.

Matt D
"NOBODY expects the Spanish Inquisition" Ximinez  ;-))

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