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Polystyrene and oil?



I have got 2 sheets 2 x 1 meters of Polystyrene (PS), 0.5mm (0.02") thick.

Dielectric constant:                    2.5
Dissipation factor (-at- 1MHz):            0.0003
Dielectric strength (0.2 mm thickness): >40 kV/mm  (i.e. >1016 kV/mil)
Water absorption:                       <0.1%

So I believed that was a feasible material for my capacitors until some of you
mentioned that it cannot stand oil. A call to the manufacturer confirmed it:
they
spoke about it standing 4 hours, maximum one week.

>From the web I found a table about PS were it was possible to see that PS
stands
SOME oils but not ALL oils. So I tested two samples of PS:

A - clear PS, 0.25 mm thick
B - white PS, 0.5 mm thick (the one for the capacitors)

I used olive (!) oil and motor oil (full synthetic). I haven't got yet
transformer oil!

Several days at 20C degrees didn't change a thing in the samples. Then I put
the samples
in motor oil to bake into my furnace for 5 hours at 75C degrees. The B
(white) sample
didn't show any visible change. The A (clear) sample lost its transparency,
became opaque.

With the aid of a microscope I saw on the B sample a lot of microscares:
still the sample is
as flexible as it was before, and the scares aren't deep.

I have read that silicon oil is used fro transformers and that it doesn't
attack most of
plactics. 

Do you know what is the oil you use for your capacitors ?

Has anybody used PS in rolled capacitors ?





________________________________________________________________________

 Marco Denicolai                   Vista Communication Instruments, Inc.
 Hardware Development Manager      www.vistacom.fi   

 marco-at-vistacom.fi                 Kaisaniemenkatu 13 A
 fax:    +358-9-622-5610           SF-00100 HELSINKI
 phone:  +358-9-622-623-15         Finland

   Remember, Murphy was an optimist! I am not...
________________________________________________________________________