i am trying to build a low inductance capacitor. I could just buy a doorknob capacitor but i don't wanna pay that much. So i know that you need a dielectric, i am using overhead transparency sheets. And im just using aluminum tape as my conductor. Now i know how to build these, i just dont know how to build it to get close to my capacitance i need. I want 4700 pf, i know i have to stack so the whole thing isnt so big. How do i figure out how big to make each sheet and how many sheets i need to get to my capacitance i am looking for. Any help is greatly appreciated!


1 Answer 1


You need to know the exact dimensions of the plastic material including the exact thickness. You need to know the exact area of the conductive material. Depending on the voltage, the conductive material should not go all the way to the edge of the plastic except at the edge where it is joined. Tape is a questionable choice of conductor. The adhesive will be an additional dielectric that you don't know anything about. It will also interfere with making a good connection at the edge.

Look up the dielectric constant for the chosen dielectric and find an online calculator to calculate the capacitance for one layer.

  • \$\begingroup\$ My dielectric is 125 micrometers thick. It can withstand 12kv. As for the tape I figured that would be a problem, i knew it would i just wanted to see what others had to say \$\endgroup\$ Dec 10, 2017 at 15:09
  • \$\begingroup\$ I was about to revise my answer re checking the voltage rating. You need to know exactly what kind of plastic you have to find the dielectric constant. An online calculator should be easy to find. \$\endgroup\$
    – user80875
    Dec 10, 2017 at 15:17
  • \$\begingroup\$ as a kid, I build a 0.0127 uF cap (computed value) of foil and wax paper. \$\endgroup\$ Dec 10, 2017 at 23:21

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