Re: GE Capacitor 42L2121

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

Original poster: "Scott Hanson" <huil888-at-surfside-dot-net> 

Like Dan McCauley and Terry Oxendale, I have used several different models
of the GE 42L metallized polypropylene capacitors in Tesla coil tank
circuits with zero failures. My MMC's are designed conservatively, with the
MMC's DC voltage rating 1.5X to 2X the RMS voltage of the power supply.

I have examined several different GE 42L's that failed in Tesla coil
service. Upon "disassembly", it was obvious that they failed by two
different mechanisms: overvoltage and overcurrent.

Those that failed by overvoltage had the polypropylene dielectric film
pockmarked by scores or hundreds of punctures, but finally failed
catastrophically when continued interlayer arcing burned a cavity through
many dielectric layers.

Those that failed by overcurrent had the metallization burned away at the
end terminations of the rolls, where a sprayed metal coating makes contact
with the metallized polypropylene and the leads are attached.

Although the Cornell Dubilier 942 series capacitors (hybrid metallized
film/metal foil) may have a bit more margin to survive "abuse" due to poor
system design or intentional overstress  ("I'll just open the safety gaps up
a little further ......."), the GE 42L caps can function with great
reliability in Tesla coil systems when their ratings are not grossly
exceeded.

  I'll continue to design conservatively and use the GE 42L's with full
confidence.

Regards,
Scott Hanson

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, March 04, 2004 2:54 PM
Subject: RE: GE Capacitor 42L2121


 > Original poster: Ethel Poulos <pulse.systems-at-verizon-dot-net>
 >
 >
 > Re: GE Capacitor Part Number 42L2121 1.2uf 1200 vdc.
 >
 > These GE capacitors are really getting hot.  They replaced an SCR
 > commutation capacitor rated at 15uf 1200v.
 > the SCR capacitor was polypropolene and aluminum foil.  the GE capacitor
is
 > metalized polypropolene.
 >
 > Is there any one that makes a polypropolyne and aluminun capacitor for
 > snubber high current applications.
 > This capacitor is used in a solid state hard tube modulator.
 >
 > I will appreciate any information or expertise you can give me.
 >
 > Many Thanks,
 >
 > John
 >
 > -