[R-390] Caps

[David Wise]

Don't let FKP1's metallization put you off.  The construction is foil...film...floating electrode...film...foil... etc.  The floating electrode is metalized, but that bit of film is not acting as dielectric; it's just a cheaper way to make a floating electrode.  There is non-metalized film to either side of it.  This is not like the hybrids, where metalized film is sometimes the dielectric.  Given the construction diagram, I can't see why they call FKP1 self-healing - it's a film-foil cap.

Dave

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Charles P. Steinmetz
Sent: Tuesday, April 30, 2013 4:29 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Caps

David wrote:

>I did a bit of shopping at Mouser, and found the following film/foil 
>C553 candidates:

>Wima FKP1 (five voltages, $1.13 at 1kV to $2.84 at 6kV)
>Wima is the cheapest and most abundant.  Are they reliable?

Wima is a very reputable manufacturer.  However, the FKP1 is a very 
specialized snubber cap, not really suitable for other uses.  Besides 
that, it is a hybrid metalized/foil.  Note that the datasheet heading 
specifically mentions self-healing ("Double-Sided Metallization and 
Self-Healing Internal Series Connection").

The Wima FKP 3 polypropylene film/foil caps are outstanding 
capacitors, but available only in the familiar Wima "box" form factor 
with short (PC mount) leads.  Nobody stocks them in the US in any 
depth.  Mouser does not stock them, but will quote.

>CDE DMT ($1.64, 630V)

The CDE DMTs are similar to 225P ODs.

>CDE WMF (axial leads!  $2.14, 630V)

I thought these were discontinued, but I may be mistaken.  Mouser has 
some stock.  The epoxied ends are not as environmentally rugged as a 
dipped cap, but that shouldn't matter for BA purposes.

Best regards,

Charles








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