# [TCML] MMC design for 12kV @ 120mA xfmr

Lau, Gary Gary.Lau at hp.com
Thu Dec 4 18:49:51 MST 2008

```64 caps?  I'm not sure it needs to be that spendy!

For a static gap and a 12kV NST, firing voltage is about 17kV.  Let's up it to 20 kV for a nice round number.

The mains-resonant cap value for a 12kV/120mA/60Hz NST is .0265uF.  I typically use 2X the mains-resonant value, but of course there's a lot of wiggle room there. So .05uF, give or take.

Ten caps per string gives a 20kV rating.  Three strings of ten caps yields a .045uF/20kV cap.  30 caps total.  If you plan to run the coil for hundreds of hours, you may wish to use a more conservative voltage rating.  But Terry Fritz experimentally determined that the life expectancy of using these caps at 2000 peak AC volts is ~70 hours, if I recall correctly.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
> Behalf Of DC Cox
> Sent: Thursday, December 04, 2008 5:57 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] MMC design for 12kV @ 120mA xfmr
>
> Each series string needs to be a minimum of 16 pcs for a 32 kV DC rating.
> Erms x 2.5 is an absolute minimum value.
>
> Each string will be 9.375 nF each, so dividing .04 / .009375 uF gives 4.2
> strings, so go to 4 strings at .009375 uF per string =  .0375 uF (37.5 nF at
> 32 kV DC) will work well with a 12/120 mA setup.
> I recommend an 8" dia sec for very high inductance ratio to give you the
> best output.  Wind 40" long with #22 AWG double-build insulated magnet wire.
>
> 64 total 0.15 uF caps required for this coil.
>
> Top toroid 24 x 6 inch size.   Dryer duct toroid will work fine.
>
> I have around 300 MMC caps (0.15 uF and 0.1 uF) in stock at present.
>
> Dr. Resonance
>
>
>
>
> On Thu, Dec 4, 2008 at 10:40 AM, John <guipenguin at gmail.com> wrote:
>
> > Planing out my MMC before I order some CD942c 0.15µF caps. I'm planing
> > on building my next coil with a 12kV @ 120mA xfmr.  LTR cap value =
> > 0.0398µF so I'm setting my cap value at 0.04µF.
> >
> > series string A: 2kV @ 0.15µF / 10 = 20kV @ 0.025µF
> > series string B: 2kV @ 0.15uF / 6 = 12kV @ 0.015uF
> >
> > Both strings in parallel giving 0.025µF + 0.015uF = 0.04µF
> >
> > Does that look good?
> >
> > --
> > <John Paine>

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