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RE: [TCML] cde 942C20P15K-F caps for sale



It's important to understand that these cap's won't "pop" with any sane overvolting.

The normal failure mode is that tiny holes are burnt into the thin-film (floating?) plate and the number of these holes increases with time, resulting in lower and lower effective capacitance.  The more severe the overvoltage, the faster these holes appear.  If you want the cap to remain within spec for years of continuous operation under worst-case temperature conditions, you'll need to adhere to the rated AC voltage spec (a LOT less than 2000V/cap).  Terry Fritz experimentally determined that the life expectancy with an applied 2000V peak 60 Hz applied voltage was something like 75 hours (from memory), which is a long time to be throwing sparks for a hobbyist, IMO.

At a minimum, the total string voltage should be the NST RMS voltage x 1.414 - at least 22kV for a 15kV NST.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Davetracer@xxxxxxx
> Sent: Tuesday, June 02, 2009 2:20 PM
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] cde 942C20P15K-F caps for sale
> 
> I'm interested ...
> 
> These are 0.15 uf caps rated at 2000V ea, right? A string of 5 would be
> rated for 10 Kv.
> 
> I may be running them in a neon sign transformer configuration. I have a
> 12kv/60 now,
> may get a 15 kv/60.
> 
> Do you happen to know how much over 12 or 15 kv I need to go to not pop the
>  caps?
> 
> Thanks,
> 
> Dave
> 
> 
> 
> In a message dated 6/2/2009 11:45:36 A.M. Mountain Daylight Time,
> forcijo10@xxxxxxxxx writes:
> 
> Hi all,  I had recently purchased 105 cde 942C20P15K-F caps for a large
> drsstc i am  building but i have made some large design changes and i can no
> longer use  them.  They are brand new never used however they are soldered
> into  strings of 5.  I am offering $15 per string + shipping or $305 for
> the
> whole lot + shipping.  Here is a pic of them in the bank i was  going to
> use
> http://farm4.static.flickr.com/3622/3567968631_ba883dd858_b.jpg
> 
> If  you are interested contact me off list, i prefer money order but if  you
> want to use paypal, i will have to up the price to make up for the 2%  they
> take off.
> 
> Thanks,  John
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