What material is everyone using these days to gap ferrite double U cores?
jpsmith123, Thu Mar 28 2019, 01:31PMI was thinking about using some 0.01" thick "Multipurpose Flame-Retardant Garolite G-10/FR4 Sheets and Bars" from McMaster Carr.
I wonder: What would be the best way to cut this stuff? If it's only 0.01" thick would scissors work, or would it chip and/or crack? Or maybe a glass cutter?
Re: What material is everyone using these days to gap ferrite double U cores?
klugesmith, Thu Mar 28 2019, 02:15PM
You could use your least favorite scissors. Or score it, preferably with a tool shape & orientation that removes material, then break.
Either way, the edge won't be pretty under a microscope, but can be deburred with sandpaper.
Why not use plastic film (e.g. acetate, Mylar) -- too hot?
Or fish paper or a manila folder -- going to get wet?
klugesmith, Thu Mar 28 2019, 02:15PM
You could use your least favorite scissors. Or score it, preferably with a tool shape & orientation that removes material, then break.
Either way, the edge won't be pretty under a microscope, but can be deburred with sandpaper.
Why not use plastic film (e.g. acetate, Mylar) -- too hot?
Or fish paper or a manila folder -- going to get wet?
Re: What material is everyone using these days to gap ferrite double U cores?
johnf, Thu Mar 28 2019, 06:06PM
I uae Kapton tape 68 microns per layer
temperature performance is better than ferrite or wire insulation
johnf, Thu Mar 28 2019, 06:06PM
I uae Kapton tape 68 microns per layer
temperature performance is better than ferrite or wire insulation
Re: What material is everyone using these days to gap ferrite double U cores?
jpsmith123, Fri Mar 29 2019, 03:04AM
Hey thanks klugesmith and johnf for the ideas.
While researching Kapton, fishpaper and mylar, I came across PEEK film and Ultem PEI film, both of which seem to have fairly good characteristics. Of these two, Ultem seems to be cheaper and more readily available, so I am leaning toward that material.
jpsmith123, Fri Mar 29 2019, 03:04AM
Hey thanks klugesmith and johnf for the ideas.
While researching Kapton, fishpaper and mylar, I came across PEEK film and Ultem PEI film, both of which seem to have fairly good characteristics. Of these two, Ultem seems to be cheaper and more readily available, so I am leaning toward that material.
Re: What material is everyone using these days to gap ferrite double U cores?
2Spoons, Fri Mar 29 2019, 04:10AM
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
2Spoons, Fri Mar 29 2019, 04:10AM
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
Re: What material is everyone using these days to gap ferrite double U cores?
jpsmith123, Fri Mar 29 2019, 01:44PM
A few years ago when I was researching insulation systems for HV transformers, I came across a few papers that touched on the aging of kraft paper, and I discovered that it's subject to several time and temperature dependent chemical processes (oxidation and hydrolysis or something like that) that cause it to eventually break down. And IIRC the breakdown process releases moisture, making it auto-catalytic.
I realize that in my low-duty application this would probably not be a factor, but being the semi-perfectionist that I am, the thought of it bothers me. So while it would probably suffice for most people, I don't like it.
(Moreover, the thought of cutting up paper bags to add to one of my transformers, also offends my gentle semi-perfectionist sensibilities :).
jpsmith123, Fri Mar 29 2019, 01:44PM
A few years ago when I was researching insulation systems for HV transformers, I came across a few papers that touched on the aging of kraft paper, and I discovered that it's subject to several time and temperature dependent chemical processes (oxidation and hydrolysis or something like that) that cause it to eventually break down. And IIRC the breakdown process releases moisture, making it auto-catalytic.
I realize that in my low-duty application this would probably not be a factor, but being the semi-perfectionist that I am, the thought of it bothers me. So while it would probably suffice for most people, I don't like it.
(Moreover, the thought of cutting up paper bags to add to one of my transformers, also offends my gentle semi-perfectionist sensibilities :).
2Spoons wrote ...
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
Re: What material is everyone using these days to gap ferrite double U cores?
klugesmith, Fri Mar 29 2019, 07:11PM
You might be amazed how many insulating parts inside pole- and pad-mounted electric utility transformers
are made from paper or wood. Might be epoxy-impregnated paper in recent decades.
klugesmith, Fri Mar 29 2019, 07:11PM
You might be amazed how many insulating parts inside pole- and pad-mounted electric utility transformers
are made from paper or wood. Might be epoxy-impregnated paper in recent decades.
Re: What material is everyone using these days to gap ferrite double U cores?
jpsmith123, Sat Mar 30 2019, 03:05AM
I know paper is widely used. And I'm sure it would work fine in my application as a spacer for a ferrite core transformer. I just don't like the idea of using it.
Another example is teflon, which I also considered. I know it's prone to cold flow (more so than other plastics) so I found a data sheet with a graph showing total deformation under various levels of compressive loading, at 100 degrees C. And I concluded that it would probably not cause a problem for me.
But the idea that the teflon sitting there squeezed between two pieces of ferrite will slowly extrude from the gap - maybe only a few nanometers per day - nevertheless irritates me, so I have to reject it.
So the problem isn't really the materials, but my idiosyncrasies...
jpsmith123, Sat Mar 30 2019, 03:05AM
I know paper is widely used. And I'm sure it would work fine in my application as a spacer for a ferrite core transformer. I just don't like the idea of using it.
Another example is teflon, which I also considered. I know it's prone to cold flow (more so than other plastics) so I found a data sheet with a graph showing total deformation under various levels of compressive loading, at 100 degrees C. And I concluded that it would probably not cause a problem for me.
But the idea that the teflon sitting there squeezed between two pieces of ferrite will slowly extrude from the gap - maybe only a few nanometers per day - nevertheless irritates me, so I have to reject it.
So the problem isn't really the materials, but my idiosyncrasies...
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