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Simple DIY capacitor

  1. Nov 28, 2011 #1
    Hi,

    I am currently working on a small project to create an simple DIY capacitor with stuff that you can get from the supermarket. Probably, I will alternate with two aluminum foils and two insulators like plastic each other, and wrap them together. Do anyone have suggestion how I can maximize the capacitor that I will constructed within a toilet roll? What is the affordable and best insulator that I may get from the store?

    Thanks
     
  2. jcsd
  3. Nov 28, 2011 #2

    davenn

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    Welcome to PF

    mylar film would probably be the best and easiest to obtain

    See what others suggest :)

    Dave
     
  4. Nov 28, 2011 #3

    OmCheeto

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    Not a clue. But please keep us up to date on your research. I've been wanting to make a Saran wrap/aluminum foil capacitor for quite some time now.
     
  5. Nov 29, 2011 #4
    Do you think mylar film will be better choice rather than saran wrap or wax paper?
     
  6. Nov 29, 2011 #5
    I will post some update once I did it. But before that, I wish to get some more feedback on what insulator layer that I should use in order to maximize the capacitance. Up to this point, I am considering saran wrap, mylar film, and wax paper. Do you have any suggestion about that?

    Thanks
     
  7. Nov 29, 2011 #6

    sophiecentaur

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    Possibly but can you buy Mylar from a supermarket? 'Cling film' will be fine as long as you are careful not to puncture it with wrinkles in the aluminium foil. For a high capacity you need as close a spacing between the capacitor plates and as big an area as possible. That means a lot of care to keep the foil un-kinked and rolled up as carefully as possible.
    I would recommend cutting lengths of foil and film and winding them on three individual 'bobbins' first and then you have the best chance of rolling them all together neatly and tightly into a cylinder. You MUST avoid a Short Circuit between the layers at all costs. Make the dielectric layer a bit wider than the two aluminium layers to allow them to wander a bit without touching.
     
  8. Nov 29, 2011 #7
    Thanks for the reply, sophiecentaur.

    I am referring the saran wrap as the Cling film actually.
    What do you mean by "cutting them on three individual 'bobbins' first and then you have the best chance of rolling them all together neatly and tightly into a cylinder"?

    By putting more insulator layer between the foil(let say 3 layer of cling film between the foils), do you think it will increase the capacitance?
     
  9. Nov 29, 2011 #8

    berkeman

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    Thicker insulation between the layers lowers the capacitance (but raises the withstand voltage). What voltage are you going to use this DIY capacitor at? How will you measure the capacitance? Is this for some contest? :smile:
     
  10. Nov 29, 2011 #9
    You r right, its sort like for contest. Capacitors will be tested for DC shorts using a precision LCR meter after the submission. The capacitor should stand 30V. Do hve any suggestion how to maximize the capacitor itself?

    Thanks
     
  11. Nov 29, 2011 #10

    berkeman

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    Since it is a contest, what do YOU think are ways to maximize the capacitance?
     
  12. Nov 29, 2011 #11
    C=E *A / d

    There are 3 ways, choose insulator with the highest permittivity, make bigger overlap area, and decrease the width between two foils. In this case, I am thinking to make bigger area and connect the capacitance in parallel. At the same time, I am still wandering what insulator layer that should I use.
     
  13. Nov 29, 2011 #12

    berkeman

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    Good. Sounds like some simple experiments could go a long way in helping you choose a dielectric material. Do you have access to the LCR meter for experiments? How about a 30V power supply? What kind of experiments would you do to figure out how best to put your project capacitor together?
     
  14. Nov 29, 2011 #13
    That is the thing, there will be a special time where student can test their capacitance during the day. Outside of that, I am not sure how to test this capacitor. What I am thinking now is to build few different capacitors and bring it during the scheduled testing time. I will probably prepare different set of capacitors with insulator between the foils, and tested the capacitance. At this point, I will not have to roll those up, since it's just a test.

    Do you think my basic idea about connecting the capacitor in parallel is okay? And do you think that I only have to work with what is the best insulator layer that I should use? Or is there any other possibilities that may work in order to maximize the capacitor? Just to make sure, you say that by adding more insulator layer is not going to increase the capacitance but will only related to let the capacitor hold more voltage, right?

    Thanks
     
  15. Nov 29, 2011 #14

    berkeman

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    We are not seeing a lot of effort on your part on this schoolwork project, beyond asking for others to do your work for you on the Internet. You need to figure out what experiments to do in your limited lab time to help you optimize your design. What experiments are you going to do?

    We don't spoonfeed students here at the PF. Show that you are doing a lot of work, and we can provide some tutorial hints. Otherwise, your thread will be closed. Learn how to learn.


    EDIT -- google Capacitor Construction. Have you at least tried that yet?
     
  16. Nov 29, 2011 #15
    I did some research on it. And the experiment what I am able to think about is to prepare several capacitance with different types of dieletric. Once I know which dielectric works the best, then I will move forward to work on minimizing the width between conducting plates, maximizing the surface area, and work on paralleling or stacking few capacitance at once. At the same time, I should reduce the air volume between the the layer.
     
  17. Nov 29, 2011 #16

    berkeman

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    Very good.
     
  18. Nov 29, 2011 #17
    I will update it back once I finished the experiment. Thanks for the help.
     
  19. Nov 30, 2011 #18

    sophiecentaur

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    I just meant that trying to spool up three strips of material - draped over a table or a chair - can easily introduce kinks and bends. If you start off with three, pre-prepared spools of tape (foil, foil and clingfilm), held firmly and under control, you have a better chance of laying them up neatly on the final article (just like a real capacitor making machine does, in fact). Neatness is everything if you want to maximise the capacity.
     
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