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Re: Polyethylene Capacitors



Tesla List wrote:
> 
SNIP
> 
>  I've just spent my
> > lunch hour calling around to the local Indiana plastics suppliers.
> > Bloomington, Indianapolis, Cincinatti and even someplace near St. Louis.
> > The prices were very high. A single sheet of 48"x96" LDPE 30 mil
> > averaged around $18 a sheet! The 60 mil averaged $34 a sheet. A
> > sheet of HDPE 48"x96" 60 mil was $43.96.
> >
> >         Please would somebody answer my question regarding 6 mil
> > thickness LDPE stacked for 90 mil thickness. Will this work and
> > are there any pitfalls?
> >
> >
> >
> > Any comments are more than welcome.
> >
> > Big Red, HV Capacitors. Burn Baby Burn.
> > ITS Member
> > D. Gowin
> 
> D.,
> 
> Stack away!  you could easily use 180 sheets of .5 mil poly and have the
> required 90 mils!  It just doesn't matter.  The cutting and aligning
> hassles are bad enough with just two sheets.  If you want to lay out time
> and  the extra effort, there is no reason why it wouldn't work.
> 
> Plexiglass is rather lossey stuff.
> 
> Richard Hull, TCBOR


All,

I note a lot of talk about air bubbles in multiple sheets.  It's not as 
bad as a single bubble in a two sheet job!  With lots of bubbles in lots 
of sheets, the voltage gradiant would distribute itself evenly and the 
air might not even corona!!!! (lotsa sheets needed).  I also note, as did 
someone else (sorry, memory overflow), that the swelling of the capacitor 
due to all the sheets and included air and poor adhesion would reduce the 
capacitance over the calculated value, SIGNIFICANTLY!!!

Again the best way is the pro way.  1 mil or thinner dielectric with end 
foil construction in two sheet capacitors with several in series.  Allot 
of you may not realize this, but in those 40KVAC CP caps, you probably 
don't have ten mils of poly separating the two high voltge end plates in 
the caps!  A superb amateur construction would be 5 - 10mil rolled caps 
in series of .1ufd each!  (Use a 20 megohm resistor across each pack in 
series).

Richard Hull, TCBOR