Re: Home-brew Capacitors

In a message dated 12/18/98 12:59:18 AM Central Standard Time,
tesla-at-pupman-dot-com writes:

> If mineral oil warps poly, why have I seen so many papers explaining that
>  cap should be filled with it? Are there any other oils that are bad? What 
> oils
>  with give a poly cap the longest life? I plan to build a vertical poly
>  cap soon, and I don't want to use the wrong materials.
>  Matt Behrend
>   Matt

   Mineral oil works fine on the thicker poly, such as 0.20" and up.  And is
OK if the capacitor is secured together, then adding oil.  My problem was
adding oil saturated paper "while" building it in flat plate design.  It would
warp after 30 minutes and trap air along with decreased capacitance.
    The corn oil has proven OK so far.  My main purpose of the oil is not as a
dielectric since many sections at in series to lower corona onset, but to help
keep the many thin sheets of poly in a stack and eliminating as much air as
  On the capacitors that I have used mineral oil and warped the poly, there
does not seem to be any electrical degradation as they still work also.  More
capacitors will be built in the coming weeks with higher capacitance values.

  If you plan on building your capacitor and securing it "before" you add oil,
it will most likely be OK.  Any warpage then will just pack the plates closer
together, a good thing. 

Hope this clears things a little bit.

Kevin E.