{"id":4284,"date":"2019-01-26T01:57:17","date_gmt":"2019-01-26T05:57:17","guid":{"rendered":"http:\/\/www.paleotechnologist.net\/?p=4284"},"modified":"2019-01-26T01:57:17","modified_gmt":"2019-01-26T05:57:17","slug":"homemade-capacitors","status":"publish","type":"post","link":"https:\/\/www.paleotechnologist.net\/?p=4284","title":{"rendered":"Homemade Capacitors"},"content":{"rendered":"

Capacitors, the electronics textbooks would have you believe, are very simple devices. In their most basic form, they consist of two conductive surfaces separated by a thin dielectric (insulating) material.<\/p>\n

Various different materials have been used over the years, from air to paper to tantalum and many more. One popular choice for dielectric material is mica<\/a> (which is also used for heatsink insulators, since it conducts heat but not electric current.)<\/p>\n

“Mica” capacitors have been made using metal deposition for decades at this point — the capacitors are much more reliable and stable this way — but the original mica capacitors from the early 1900s were simply pieces of mica clamped between two metal plates.<\/p>\n

I don’t have the necessary equipment to attempt metal deposition, but old-school clamped<\/em> mica capacitors don’t require very much in the way of equipment. The secret ingredient, of course, is the mica. While on vacation in Maine last month, I came across a large specimen for sale that looked like it might produce nice, clean sheets.<\/p>\n

\"\"<\/a>

A chunk of mica, as it might be found in nature. (Click for larger.)<\/p><\/div>\n

This is one of the nicest pieces I’ve seen. I don’t feel too bad about experimenting with it, though. The reason mica works so well as a dielectric is that the individual sheets are extremely thin — so very little is needed. (Single sheets from this one seem to be about 20-30um in thickness, although this is on the edge of what I can measure reliably with digital calipers.)<\/p>\n

\"\"<\/a>

30um thickness, to something like one sig fig or so…<\/p><\/div>\n

Using a razor blade and some patience, I was able to lift a layer of mica from the chunk. I then cut it to a roughly rectangular shape. Next, I made a template from an old business card that was slightly smaller than the piece of mica. I used this template to cut two pieces of aluminum foil, making sure they were slightly smaller than the piece of mica.<\/p>\n

\"\"<\/a>

A single layer of mica (more or less). Click for larger.<\/p><\/div>\n

The next step was to sandwich it all together. I used more pieces of business card to insulate the outside, allowing the use of alligator clips to clip on to the mica. I then connected the jumper cables to a component tester.<\/p>\n

\"\"<\/a>

The inner part of the sandwich. The two metal plates must not touch.<\/p><\/div>\n

The verdict: It works! The component tester shows a capacitor of roughly 80pF (and shows no component when one of the wires is disconnected at the cap.) The capacitance doubles to ~160pF when I hold on to the paper insulation — and almost quadruples again, increasing to nearly 600pF, when I squeeze it together. Time to 3D print a compression jig!<\/p>\n

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It works!<\/p><\/div>\n

After printing a simple compression frame, the capacitor ended up at about 214pF. This is less than when I was holding the leads — but it’s more consistent and a lot more reliable this way, even with a very simple frame.<\/p>\n

\"\"<\/a>

A working, 220pF-ish capacitor.<\/p><\/div>\n

Strips of metal, interleaved with sheets of mica, might help it get up into the nF range. But that’s a project for another day.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Making a working homemade capacitor with mica, aluminum foil, and a 3D printer. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"footnotes":""},"categories":[503,219,265,238,226,385,235,1],"tags":[529,528,527],"class_list":["post-4284","post","type-post","status-publish","format-standard","hentry","category-3d-printing","category-analog","category-components-electronics","category-electronics","category-how-to","category-mad-science","category-science","category-uncategorized","tag-3d-printer","tag-capacitor","tag-mica"],"_links":{"self":[{"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/posts\/4284","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4284"}],"version-history":[{"count":8,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/posts\/4284\/revisions"}],"predecessor-version":[{"id":4314,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=\/wp\/v2\/posts\/4284\/revisions\/4314"}],"wp:attachment":[{"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4284"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4284"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.paleotechnologist.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4284"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}