Re: Mylar sheeting

To: tesla-at-pupman-dot-com
Subject: Re: Mylar sheeting
From: "Harri Suomalainen" <harri.suomalainen-at-pp.inet.fi> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Mon, 19 Apr 1999 18:52:33 -0600
Approved: twf-at-verinet-dot-com

>Can anyone tell me what the dielectric strength of mylar is per mil of
>thickness? I am building a custom made transformer and I want to use mylar as
>an interlayer insulation.

DuPont's web site has specs available. It depends on the exact grade of mylar
and foil thickness. If my memory serves well, mylar B at 1mil thickness is
specified for 100kV/mm (2.5kV/mil) !! Check the site for further info on
the exact type and thickness.

Just a suggestion: overdo it. Use more insulation than you'd actually need.
Use multiple
layers at critical points just in case some layer does break. In
transformers there are
usually two reasons for mylar anyway: insulation and getting a nice flat
surface to wind
next layer on. Something like 1mil foil certainly won't satisfy the flat
surface requirement.

There is another reason for using thin foils. Heavy mylar is not too nice
to bend if a very
tight transformer is wanted. It is much easier to use couple of thinner
layers. Especially
in switch-mode power supply ferrites (small!) you'll notice this in no time.

Harri