Re: Polyester Film Capacitors

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Oops!  The dissipation is 0.0007 not 0.07 so it only runs 7 times hotter :-)

Cheers,

	Terry

----------------------------------------

Hi Duncan,

Polystyrene is alive and well and is commonly available as a capacitor
dielectric.  However, the newer films are much more popular and are getting
designed in as just the defacto standard.  Polystyrene's dissipation factor
is 0.07 compared to polypropylene at 0.0001  That means they would run 700
times hotter in our favorite application ;-)  There are many high voltage
films out there, but we need super low dissipation factors.  Such caps also
have high dV/dT and low inductance which we love too.

Cheers,

	Terry


At 03:49 PM 3/27/2001 +0100, you wrote:
>Hi All!
>
>
>
>>Polypropylene caps are the lowest-dissipation high-voltage
>high-current
>>caps out there
>
>They probably are, but I can't help wondering . . .
>
>Purely out of idle curiosity, has anyone ever seen high voltage high
>current rated polystyrene caps?  Based on the dielectric properties of
>polystyrene they ought to be pretty good too.  I have an illustration
>in a book from 40+ years ago showing metal-cased polystyrene caps of
>generous dimensions with the usual massive ceramic standoffs on them
>and evidently intended for HT valve circuitry, but the British company
>which made them (TMC in Orpington) no longer exists.  Just wondered if
>anyone still produces such things.  The only polystyrene caps I've
>seen recently are the small signal, low loss 160V jobs for your
>average silicon circuitry.  I'm just wondering if there's a good
>reason why we don't see hefty polystyrene caps, but from a polymer
>chemistry view of things I can't think of a single reason why they
>shouldn't be made.
>
>Dunckx
>