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 8:04 AM, Chuck Olson <[email protected]> wrote:

> I did that rewind in 1977 while in college and then never another, I
> guess that says something :)
> 
> As you might imagine I enjoy collecting project info off the internet,
> just need to translate those ideas into more actual artifacts !
> 
> Hope you fare well with this project.
> 
> Best Regards,
> Chuck, WB9KZY
> 
> 
> 
> On Thu, Jan 23, 2025 at 8:41 AM madscientistatlarge
> [email protected] wrote:
> 
> > "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.
> > 
> > On Thursday, January 23rd, 2025 at 7:17 AM, Chuck Olson [email protected] wrote:
> > 
> > > BTW McCoy had another similar article: Tailor-Made Volts in the Feb
> > > 1964 issue of QST:
> > > 
> > > https://www.worldradiohistory.com/Archive-DX/QST/60s/QST-1964-02.pdf
> > > 
> > > He mentions 7 hours, how much is 7 hours of an engineers time worth ? :)
> > > 
> > > Best Regards,
> > > Chuck, WB9KZY
> > > 
> > > On Thu, Jan 23, 2025 at 8:03 AM Chuck Olson [email protected] wrote:
> > > 
> > > > If safety was my primary guide, I'd grit my teeth and buy something commercial.
> > > > 
> > > > The editor of QST was electrocuted in 1938 while doing some
> > > > ill-advised experimenting with TV - he literally had a doctor in the
> > > > house, no help.
> > > > 
> > > > Best regards,
> > > > Chuck, WB9KZY
> > > > 
> > > > On Thu, Jan 23, 2025 at 7:53 AM madscientistatlarge
> > > > [email protected] wrote:
> > > > 
> > > > > "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.
> > > > > 
> > > > > On Thursday, January 23rd, 2025 at 6:31 AM, 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.
> > > > > 
------------------------------
> > A bobbin always seemed like a good idea, too much insulation is a minor problem, too little can indeed be fatal, rapidly (and the whole point of using an isolation transformer for this, I'd hate to put the work in and die anyway!) I'd planned on wearing gloves, I know how dirty even clean hands are. Sorry about the bad sentences, it's starting to be another bad day for me. I won't be fully properly conscious all day with various faculties fading in and out. It's what I call a "supportive care" day and I just have to remind myself that all I'm doing today is try to manage the situation and hopefully be able to eat at some point. Oddly I find I still have a real taste for life.

Again, thanks to all.  I will be grounding the core and have a pair of ground plates isolating the cores (2 overlaping "U" structures so as not to create a shorted turn, probably on opposite sides of a pcb with a single through hole to ground them both).  And I'll check the leakage current to those plates and the core.  I have an instrument transformer and can get 440 ac out of it (backwards, not ideal but usable at very low power).  Not as high as I'd like for a hipot test but adequate with grounding anything that current shouldn't be flowing through.  Precious little information about this on the web, likely due to legal issues and the fact that U.L. has no standard for the required insulation strength that are prescriptive, just that you have to keep the leakage under a limit.  Nearly all information I was able to find on the web about this applies to higher voltage transformers that are usually in an oil bath as part of the power grid.  Then again, talking to a utilitty guy a couple of years ago, those big substation transformers start at about a million dollars!  Give the value and hazards associated with large transformers has probably convinced people that every one needs to know what works and what doesn't.  I should mention there is kapton for masking that's anti-static, that's not what you want for insulation, you want a variety designed for insulation!

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