Re: Oil Caps

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Actually, there's lots of info on oil dielectric caps in the archives.  The
breakdown voltage of oil isn't infinite, however.  Figure on 100 kV/cm as a
starting point.  It depends a lot on dissolved/suspended water, gases, and
particulates.  For liquid insulators, purity is important.
http://home.earthlink/~jimlux/hv/insulliq.htm has more info.

Suitable oil (i.e. electrical insulating oil, like Shell Diala AX) runs
around $25 for a 5 gallon pail.  You can also use mineral oil from the feed
or drug store, but you DO have an issue then with water, and the price is
about the same.

Castor oil is used in some capacitors, the primary advantage being higher
epsilon (ca 4), for more C in a given size.  The breakdown is about the
same as most other insulating liquids, but the cost is higher, particularly
in small lots (I suspect that like most other liquids, it's about the same
cost in 1000 gallon truckload lots: $2-3/gallon)

In a classic oil insulated capacitor, the plates are spaced by kraft paper
(i.e. thin brown paper), but oil is actually the dielectric.  For TC use,
most use polyethylene as the dielectric in combination with the oil.  For
any layered dielectric, more thin layers is better than 1 thick layer (so a
defect/pinhole, etc. in one layer doesn't cause breakdown)  Plastic bags
have been used, as has various sheet polyethylene materies, and so forth.



Tesla list wrote:
> 
> Original poster: "Johnson, Jeffrey D -at- PWC by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jeffrey.d.johnson-at-l-3com-dot-com>
> 
> Greetings everyone,
> I would really like to use the Geek caps everybody is so happy with but it
> seems their availability is limited.  I only have a few things left to do to
> finish my coil and can't wait several weeks.  The Panasonic caps in Terry's
> web page (.056 uF, 1600V) caps are too expensive (according to MMCcalc I'm
> over $100 for my planned cap).  So I was looking at oil as a dielectric.
> Epsilon r of mineral oil is 2.22, tand < 0.0005 and infinite puncture
> voltage.  I haven't seen any discussion of this on the list (I haven't been
> on for that long however).  Any thoughts on feasibility, etc.  Oh yeah, any
> design information?
> 
> Jeff Johnson
> slc, ut