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Re: All Oil Cap
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Friday, September 19, 1997 5:53 PM
To: Tesla List
Subject: All Oil Cap
>
>
> From: Dennis Hoffman[SMTP:hoffman-at-werewolf-dot-net]
> Reply To: hoffman-at-werewolf-dot-net
> Sent: Friday, September 19, 1997 12:22 PM
> To: tesla-at-pupman-dot-com
> Subject: stacked plate capacitor
>
> Hello all,
>
> I was thinking about building a stacked plate capacitor using oil
as the
> dielectric and completely eliminating the polyethylene. This
should make
> the cap more bulletproof as to overvoltage conditions. Has anyone
ever
> used galvanized steel cut into squares to construct one of these?
Also, is
> it better to go with larger plates with a wider gap between them
or
> smaller plates with a closer gap? Any comments would be greatly
> appreciated.
>
> Thanks, Mike H.
>
>
Dennis,
galvanized steel seems like overkill. You can get adequate structural
integrity with rigid thin aluminum plates. Much lighter and generally
less expensive. Of course if weight is not a problem, and you have an
inexpensive source, then go for it.
Whatever form of metal you use, clean the surface well and degrease
thoroughly before final assembly. I suggest wearing latex gloves as
body oils can cause problems.
Since you are using only oil, go for larger plates further apart (but
see remark below about bowing). One thing you have to watch out for
is the sharp edges. There will be a real tendency for fields to build
up at the edges, and this can cause breakdown. Curve the edges
instead of having a 90 degree cut, if possible. Sanding all edges so
they are smooth may help a bit. How will you be maintaining
structural rigidity? Make sure the individual plates are as parallel
as possible. Arrange vertically if possible. Such a cap may be used
minutes after it is constructed, assuming you have shaken the unit to
dislodge little surface bubbles. A brief break-in at reduced power
levels is still suggested, as the unit will then have an opportunity
to work loose and absorb any tiny air bubbles still on the plate
surfaces.
Be aware that when powered the plates will be strongly attracted to
one another. Failure to take this into account can lead to the plates
bowing and possibly initiating an arc through the oil. Any such arc
will instantly make the oil turn dark and cloudy wherever the arc
established itself. As plates become larger, the tendency to bow will
increase.
An all-oil capacitor is capable of tremendous abuse so long as you
don't get internal arcs. Oil has a low dissipation factor, so doesn't
heat as much as poly. Also, the oil can circulate a bit, and thus
more heat can be tolerated. Such circulation is based on the hotter
oil rising, and it is an action you get for free. Oil depth along the
top of the cap must be at least an inch.
Avoid resting cap plates along the bottom. To do so is to invite a
surface arc, which can travel many times further than an arc through
the oil!!!
Hope this helps.
Fr. Tom McGahee