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Re: Maxwell 31159 cap on eBay

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 08:30 AM 6/22/2004 -0600, Tesla list wrote:
>Original poster: Ed Phillips <evp-at-pacbell-dot-net>
>Tesla list wrote:
> >
> > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
> >
> > Your assumption is correct --- they are built differently.  The difference
> > is a Maxwell trade secret that they will not reveal.
> >
> > D
>         OK - trade secrets can be very important.  Presumably the capacitors
>with smaller reverse voltage ratings are built that way because they can
>be sold for a lower price and/or smaller in size.  Any of that correct?

Indeed, Maxwell has trade secrets, but I will guess that they are in the 
manufacturing processes, not the design.  Any would-be pulse cap mfr could 
buy a set of Maxwell caps of various types, saw them open and easily 
determine what the dielectric materials are and the construction of the 
innards, etc.

What Maxwell has, and the would-be knock off mfr does NOT, is people and 
procedures that enable them to consistently produce them.  Even if Maxwell 
were to publish all their design rules (and, frankly, I think they have, 
over the years, published enough conference papers, etc. that lays out all 
the stuff), I doubt that anyone else could use them to make capacitors that 
are the equivalent.  What Maxwell does not publish is things like how their 
winding machines work, what tensions they wind at, how they test, how they 
do the impregnation, and so forth.

There's a lot more to building any high performance widget than merely 
having the bill of materials and the construction drawings.

What Maxwell also has is engineers who understand the specific applications 
of their products to a variety of uses.  They know how to specify designs 
from their "library" that will optimally meet a particular need.  Sure, one 
could just use the catalog numbers and the derating curves and do it, 
adding in some extra margin, but if you were an equipment manufacturer, 
trying to reduce the BOM cost of your pulse cap containing widget, you'd 
want some help selecting the part that is neither too big nor too small, 
but, like chair size and temperature of porridge, just right.

In Maxwell's case, they have a certain range of "sub capacitor" units that 
are easily producable (for them), and they have to series/parallel 
mix/match them to get what the user wants, and it's not always achievable 
(energy storage and inductance push in opposite directions for 
instance).  They also have all the test data needed to make rational life 
predictions for their components, and can produce a test article for 
accelerated test and have confidence in the results.