RE: capacitors

To: tesla-at-pupman-dot-com
Subject: RE: capacitors
From: "Payne, Will E" <will.e.payne-at-lmco-dot-com> (by way of terryf-at-verinet-dot-com)
Date: Tue, 25 Aug 1998 17:42:11 -0600
Approved: terryf-at-verinet-dot-com
Never re-invent the wheel while on a steep hill  !

I'm probably running 2 to 3 kV per mil, but maybe this is still possible.
So far I have blowed up two PSWCs, the first lasted 10 sec the second one
survived 3 min.  If I can cut the E-field in half again, that would give a
life of 1.5 hours.  According to you, if I take a PET plastic dielectric
capacitor with a rated life of 100,000 hours to 3x its design voltage, it
should survive 400 hours.  At six times over voltage, it should survive 10
hours.  Corona problems are still my main concern, although none of the
Tesla List responses specifically mentioned corona in their PSWC attempts.

Since the Tesla list is generally interested in high voltage caps and
especially home grown ones, I'm forwarding your experience to the Tesla list
server unless someone objects.

Will

ps : Mike Foster tells me the PET in soda bottles is molecularly oriented as
a byproduct of the blowing process.  My CRC handbook does not list the real
part of the vector permittivity nor the dielectric strength.  Yes, I know
about teflon, but unfortunately have no source of cheap Teflon soda bottles
;-)

> ----------
> From: 	Kip Turner[SMTP:kip-at-mindspring-dot-com]
> Sent: 	Tuesday, August 25, 1998 12:21
> To: 	will.e.payne-at-lmco-dot-com
> Subject: 	capacitors
> 
> Will,
> 
> As mentioned by one of your respondents, Mylar dielectric film is grain
> oriented PET. I don't know if the soda pop bottles are or not.  The DF
> (Dissipation Factor) is about 1 % at low frequencies(the dielectric
> stuff).
> If heated above about 150 C, it will un-orient and the DF (DF= watts/VA...
> like power factor) will increase to 3 or 4 %. I never checked it at RF
> frequencies. Obviously, it's rather lossy for RF use.  Teflon as a DF
> of about 0.01%...a factor of 100 lower.
> 
> I highly recommend the oil floating on the electrolyte, to reduce corona
> which is very damaging to the dielectric.  You may have a higher than
> average field at the edge of the electrolyte.  Life on a dielectric
> varies approximately as 1/(E^5) where E is the field intensity in the
> dielectric. Working fields, depending on life requirements, are usually
> in the range of 600 to 1,000 V/mil for foil construction.  Self healing
> types, such as electrolytic and metallized dielectric construction operate
> at somewhat higher fields, though a lot of the space saving is the lack
> of foil (typically about 6 micron thick).
> 
> Hope this helps you to estimate life.   Remember...corona in a capacitor
> is
> a NO-NO !
> 
> 73,
> 
> Kip
>