# RE: MMC resister problem

```Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

I can vouch from experience that a charge sufficient to make a healthy
"snap" when shorted exists on individual MMC caps after the power is turned
off, even though the MMC end-terminals are shorted by virtue of the NST
secondary.

It's not at all clear how these asymmetrical residual charges came to be.
If individual caps have slightly different capacitance values, then their
respective voltages will scale inversely with their value, but there's no
(apparent) way that they can develop a voltage reversal with respect to
others in the string.  Same thing with unequal leakage resistance.
Something non-linear must be going on.  Could there be some rectification
occurring as the corona inception voltage (AC voltage rating) of the caps
is exceeded?

But the fact that such unequal residual voltages does exist has some
troubling implications for the MMC's voltage rating.  Say we have a string
of ten 2000V caps and we want to charge the whole thing up to 20kV.  Fine,
that's 2000V per cap.  But if one cap has an initial charge of 500V, then
we've exceeded it's rating by that much.

So, it may be that the value of individual bleeder resistors goes beyond
personal safety and benefits the well-being of the caps.

Gary Lau
MA, USA

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, June 03, 2002 8:36 PM
Subject: Re: MMC resister problem

> Original poster: "david baehr by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<dfb25-at-hotmail-dot-com>
>
>
> I think some of the large commercial made caps use many' packs' of caps in
> series inside them........do they put resistors on each pack in these
> caps???????
>
Nope, but as pointed out in a subsequent post in response, they are in a
sealed container, not intended for access at any time after manufacture, so
the safety implications of voltage on the individual units are negligible.
The external user cares not what the inside does, since all they can see is
the exterior terminals, and those CAN be discharged to zero with a short or
bleeder.

This might have life implications though... keeping a capacitor charged puts
mechanical stress on the innards..... Such things are probably one of many
of the factors affecting rated life of commercial pulse caps.

```