Re: [EE] kapton thickness for transformer

"Human beings are the only creatures on earth that claim a god, and the only living thing that behaves like it hasn't got one.  Does the world belong to no one but you?"  The Lobster in "The rum diary"


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On Thursday, January 23rd, 2025 at 6:41 AM, David Robertson <[email protected]> wrote:

> I thought transformer winding tape was usually polyester rather than
> polyimide.
> 
> David
> 
> On Thu, Jan 23, 2025, 08:34 Chuck Olson [email protected] wrote:
> 
> > Forgot the link to the November 1976 issue of QST with the Ugly
> > Duckling article :
> > 
> > https://www.worldradiohistory.com/Archive-DX/QST/60s/QST-1976-11.pdf
> > 
> > Best Regards,
> > Chuck, WB9KZY
> > 
> > On Thu, Jan 23, 2025 at 6:47 AM Chuck Olson [email protected] wrote:
> > 
> > > I only rewound one transformer, never wound one from scratch. Lew
> > > McCoy had an article in November 1976 QST on the "Ugly Duckling" where
> > > he rewound an old TV set transformer for a low voltage (18 volt)
> > > output (can you say E I ?). He left the primary alone and also the
> > > insulation over the primary. The secondary windings were gauged by
> > > the number of turns on the 5 volt winding.
> > > 
> > > My victim was a non-working Knightkit tube amp (KG-240 ?) - it still
> > > works but it buzzes and the laminations do kinda warm up :)
> > > 
> > > In these modern times I'd consider a design for a 3D printed plastic
> > > bobbin - usually the primary and secondary are two windings side by
> > > side separated by plastic - check the data for Tamura (or other
> > > brands) of transformers for ideas.
> > > 
> > > If this is a toroid, yikes, good luck on that !
> > > 
> > > There is a book on tubebooks.org on transformer design:
> > 
> > http://www.tubebooks.org/Books/Lee_1955_Electronic_Transformers_and_Circuits.pdf
> > 
> > > Best Regards,
> > > Chuck, WB9KZY
> > > 
> > > On Wed, Jan 22, 2025 at 10:53 PM madscientistatlarge
> > > [email protected] wrote:
> > > 
> > > > I'm building a large isolation transformer (1KW+-) on a laminated
> > > > steel core. How much kapton is typically used for insulation between the
> > > > windings and the core, i.e. how many 1 mil layers (or 2 or 5 mill is also
> > > > available).? I know that surviving power spikes requires planning for
> > > > 10KV+ surges. I'm thinking 4 or 5 layers at 1 mill thickness? Lets say
> > > > the voltage is 250V (I'll also be using the output in series with the
> > > > outlet to get "220" V). I'm in the U.S. so power line is about 127V (they
> > > > keep creeping it up to increase power levels). Thank you.
> > > > 
> > > > "Human beings are the only creatures on earth that claim a god, and
> > > > the only living thing that behaves like it hasn't got one. Does the world
> > > > belong to no one but you?" The Lobster in "The rum diary"
> > > > 
> > > > Sent with Proton Mail secure email.
> > > > 
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Both are available, similiar cost between Kapton and the polyester.  A web search mostly turns up the grade for masking powder coating, but the type inteneded for insulation is available.  I'll see if I can track down a source.  My only issue with polyimide is that it's halogenated so if you do manage to get it way, way too hot it's bad.  I already have the wire, with polyimide but that coating isn't thick.  Then again, I shouldn't ever get it near the failure temp.  Mostly I'm over designing so it can tolerate occasional abuse (long enough so I realize it or a fuse pops), because that happens in a lab.  Also I can put in a thermal fuse without too much worry about nuisance trips.

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