Re: MMC resister problem

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Voltage reversal is possible in a series of capacitors the same was it is in
"unbalanced" nicad battery packs.

If your cap string is building up voltage due to hysteresis and a few caps
don't make any voltage themselves (leakage capacitance or combination of
both) and the entire string has a load of some sort like your transformer
secondary, they become part of the load and will see a voltage reversal and
possible charge up from this current flow.

KEN



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, June 04, 2002 9:01 AM
Subject: 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>"
> <jimlux-at-earthlink-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.
>
>
>
>
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>
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>