Re: Maxwell Capacitor abuse, voltage reversal?

To: tesla-at-pupman-dot-com
Subject: Re: Maxwell Capacitor abuse, voltage reversal?
From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 02 Feb 2000 11:47:08 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme



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> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Maxwell Capacitor abuse, voltage reversal?
> Date: Wednesday, February 02, 2000 3:44 AM
> 
> Original Poster: Adam <adamsmith-at-mediaone-dot-net> 
> 
> Re: will I need to series-parallel my 40kV maxwells...
> 
> > Original Poster: "Megavolt Nick" <tesla-at-fieldfamily.prontoserve.co.uk>
> > 
> > It depends very much which type they are.  With all tank caps the
crucial
> > thing is the Ipeak not the Vpeak therefore you should be fine up to a
few
> > kVA as the V peak off a 15kV neon is no where near 45kV (35kV tops).
> 
> Well, I'm not sure that the Maxwell's I'm getting are the ideal type for
> Tesla Coil use, but they're all I could get my hands on.  They look like
the
> type "SP" shown on this site: http://www.surplussales-dot-com/Maxwell.html
> 
> The Maxwell part numbers are: 37218, 31507, 31677 and 31393, but I don't
> have access to the datasheets.  Except for the 31393, these are no longer
> listed on Maxwell's site as best I can tell.  The voltage ratings are
just
> 40kV, AC or DC is not specified.  The current ratings are 25kA pulse, 25A
> rms, but these are all at 20% "voltage reversal".
> 
> If someone could explain the definition of the voltage reversal
percentage
> to me, it would be quite helpful.  Do they they mean the peak-to-peak
> voltage divided by the rated voltage?

Reversal is how high the "negative" peak is on the damped sine wave
compared to the original charge voltage.  In a TC application, VR would be
quite high, say 80%, which dramatically shortens cap life.  It is related
to Q. High Q (low loss) means that the circuit "rings" for a long time,
meaning that each successive cycle is almost as big as the previous one
(i.e. big VR percentage).  A constant amplitude sine wave is a VR of 100%. 
A critically damped discharge (with no overshoot) is a VR of 0%

The voltage rating is peak DC voltage: these aren't designed as filter caps
to hold a constant voltage, rather, you're supposed to charge them up and
then discharge them.  The 25A RMS rating is the important one for you,
because it is limited by the heat buildup in the cap. 




> 
> -Adam
> adamsmith-at-mediaone-dot-net
> 
>