Re: stacked poly cap

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Hollmike-at-aol-dot-com>

Justin, 
    I bought a sheet of this once and it seemed very suitable for a homemade 
cap.  The thickness is 62.5 mils.  For a straight DC charge, it would likely 
be good to as much as 60kV, but since this is high frequency, you must derate 
considerably.   I would estimate that it would be good for about 20kVAC as 
far as puncture resistance.  The border you leave around the foil(I cut 
plates from aluminum flashing myself) will be a bigger issue.  In a couple of 
tests I did, I caused carbon tracking from the edge of the plates and around 
the plastic.  I would use at least 1.5 to 2 inches of border around them and 
make extra allowance in the spot where the tabs (for connecting the plates) 
protrude. 
Mike 


>
> I was thinking of building a stacked poly cap using the HDPE sheets 
> available 
> from McMaster-Carr. I wanted to use the 1/16" thick sheets. They are pretty 
> cheap ($1.67 I think.) Does anyone know what voltage the sheets should be 
> able to withstand? I haven't been able to find reliable information on the 
> dielectric strength of HDPE. Almost everything I have seen has a had a 
> different value for the dielectric strength. Also, I was wondering if 
> someone 
> could give me the formula for calculating the capacitance of a plate cap. 
>                                    Justin 
>
>