Re: [TCML] pulse cap specs

[Jim Lux <jimlux@xxxxxxxxxxxxx>]

Yurtle Turtle wrote:
> I run my pig at 280 in, yielding 16.8 kV out. My safety gap is set
> just above that. I run my MMC (Multi Maxwell Cap) at five strings of
> two, or 75 nF 70 kV.
>
> Adam

In that case, you'd expect pretty good life. 16.8 kV (rms?) is about 
23.5 kV, call it 24 kV.  Compared to the 70kV rated voltage for the 
caps, you're about a factor of 3 undervoltage.

Using the formula from Maxwell
Lx = Lref * (Qref/Qx)^1.6 * (Vref/Vx)^7.5

Qref is the Q for 50% VR (which is what the cap is rated for) or about 2
Qx is what your tc is running at perhaps 10-15.

(2/15)^1.6 * ( 3)^7.5 = 0.03 *3800  = over 100 times the life...




> --- On Thu, 5/22/08, Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:
>
> > From: Jim Lux <jimlux@xxxxxxxxxxxxx> Subject: Re: [TCML] pulse cap
> > specs To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Date:
> > Thursday, May 22, 2008, 8:46 AM Yurtle Turtle wrote:
> > > These caps hold up just fine in Tesla duty. I've
> > got ten and have
> > > never had a problem, even when pushing them over 400
> > bps. The spec
> > > sheet says they're good to 500 pps. The only
> > problem is that you
> > > don't know how much abuse they'veseen before
> > you buy them. Keep in mind that pulses/sec is not breaks/sec, at
> > least as defined by the cap mfr.  A TC typically runs at almost 90%
> > reversal, which is a lot harder on the cap internals than the 20%
> > or 50% often spec'd in the capacitor data sheet in connection with
> > the life spec.
> >
> > OTOH, reducing the voltage across the cap by a factor of two has a
> > HUGE effect on life.
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