Re: [EE] kapton thickness for transformer

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:
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> "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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> 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.
> > > >
> > > > I'll read that. I intend to be conservative on this, and apply some derating. I may make a bobbin, though I could just put a plasic disc between primary and secondary. I was planning on side by side with a gap/insulator. The whole point is safety, I really, really hate getting shocked, I've had some good ones (BAD!). One nice thing about kapton/polyimide is that it doesn't track much, i.e. an arc usually doesn't make a conductive carbon path on the surface when heated by an arc. The arc heating is actually why you feel static electric shocks with door knobs and such.
> > > >
> > > > I'm thinking of gluing a bobbin together. Transportation is a problem for me, but there is a local hackers gild with all the neet stuff (They were just recently gifted a 2.4kw laser that's probably been refurbished by now. More importantly 3D printing both with filament and liquid polymerization. I could probably find one online. A bobbin would definately work best, and makes it easy to wind off the transformer, I could hack together something to turn it slowly pretty easily. I am sure it will tend to deter me from rewinding other transformers but I have time and little $$ Though I can now spend something on my hobbies. I won't be ordering materials until the first part of next month so I have plenty of time to think and try not to be stupid. I've worked in life safety, we all make dumb and dangerous mistakes more than most people realize.
> > > >
>
> Not too worried about spending time.  I'm disabled and with the health issues never got my degree (or I'd be making high 6 figure by now, I was going for a PHD ultimately.  On a good day still test so well that you learn the test isn't adequate to evaluate me.  I've done this on IQ and vocational testing.  I finish parts of the test no one finishes and get it right.  Testing and life experience has shown me I can do pretty much anything my body is up to.  This type of thing mostly keeps my brain ticking over and reduces boredom.  It's first and foremost for fun overall.  I am in my sixties, a real grey-beard.  I assumed the winding part would be tedious.  A lot of things look like more fun than you find out they are when you do the thing.
>
> 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.
>
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