Roll your own capacitors


Rolling your own electronics components can be fun, but can also help in explaining how certain items actually work. [Addie] from The Toymakers recently set off to figure out how capacitors work, by making her own.

She understood the general concept behind capacitors and how they are constructed, but she wanted to see how it was done first-hand. To construct her capacitor, she selected aluminum foil as her conductor, and saran wrap as the dielectric. She admits that her first attempt was a failure, but undaunted, she carried on. Friends suggested that her conductors were a bit too small to hold any reasonable charge, so she tried larger sheets of aluminum foil to no avail.

She kept at it and found success after using several feet of foil to construct her capacitor. She charged it with a handful of AA batteries and was excited to see her multimeter come to life when she touched the leads to the cap.

While you likely wouldn’t use a hand-made capacitor in your next build, it is a fun experiment to do with children interested in learning about electronics.

[via Adafruit blog]

29 thoughts on “Roll your own capacitors

  1. We did this as a project in my highschool electronics program. We were also scored on the total capacitance we achieved. This put an element of competition into the project and some of us did research to try and give us an edge.

    Good times

    1. Hai DerAxeman,

      I see ur comment about DIY capacitor here. I said that you sort like winning a competition for making DIY capacitor. At the same time, I am also working on the same thing. Mind to share or suggest some ideas? I know how the basic works, but not sure how to maximize the capacitance in this case.


  2. I have no idea what the relationship is, but I suspect that using an even longer strip might be still more effective. Also a different dielectric is probably even better. Granted, this is easier and safer in some ways, but a saltwater leyden jar ( probably makes a better capacitor.
    Anyone know why the author of that instructable calls it a high-voltage capacitor, I assume that to be a context thing and not a general rule.

    This is an interesting air capacitor for ham radio stuff->

  3. Probably could have gotten a little more from it had she put the saran wrap on top as well at the end, since the foil touching itself would lower the surface area of one panel.

    1. Yes, but after the bomb drops, I will be more concerned about replacing all the burned transistors and constructing IC replacements. Now all we need is a diy transistor and diy diode. Diy resistors are easy.

  4. When building caps it isn’t so much the thickness of the material but the number of layers. You can construct caps really easily with copper clad pc boards. Stack single sided boards on top of each other.

    Back before the laser diode was possible we used glass to make capacitors for the laser power supplies. Stack sheets of glass on sheets of 1/8″ aluminum for 25 pairs in each stack. Sheets were 2 feet square and wired in parallel.

  5. We did this in the first level ee lab. Had to make one, calculate the capacitance, and compare results. Also made paper resistors and had to find the max voltage they could handle before catching on fire. Fun lab.

  6. I remember ten years ago when I was building a Tesla Coil, which needs a capacitor than can take 10k or 20k volts, which isnt all that common. Most of the tutorials said to get a big vat of oil and fill it with alternating sheets of glass and aluminum. The whole setup would have weighed 50 pounds or more and been almost impossible to transport.

    Instead, I went on ebay and bought some 30kv capacitors from a laser power supply from Los Alimos National Labs for $75. They work great.

  7. This is a fine explaination of the basics. But a more refined and useful technique is documented over at the 4HV (For High Voltage) wiki:,_3.5_nF

    “The capacitors are based on PP copolymer foils used in laser copiers and printers. Each sheet should stand 14 kV and depending on how many sheets you use you can get different capacitance (two sheets 9 nF – six sheets 3.5 nF). The foil is thick kitchen aluminium-foil (for grilling).”

    I’ve made a couple of these myself and they stand up to abuse well. The kind of experiments you don’t want to risk your ceramic doornob caps on.

  8. ok… now I am sure many a person has mentioned how this could go mental… but this site gives a mathematical way of working out how many Farads a capacitor has/is.

    so… a a roll on aluminium foil (two to be precise) is easy enough to buy, say 300mm wide and 10m long (my maths makes that 3m squared… waked paper, or baking paper has a ‘permittivity’ of 2.5 (apparently) and is less then 0.01 mm thick (I would say) or 0.0001m which means two rolls of foil could give make a capacitor that is 75,000 Columns… which is an insane amount of charge is it not?

    Am I missing something here or is it really that easy to ‘roll’ something that could easily be used to yield insane amounts of POWER!

    1. Your math is incorrect, you did use the numbers given on the website but that site failed to provide you with the correct absolute permittivity. It does say you have to use the absolute permittivity of a dielectric next to the equation but it fails to provide the absolute permittivity.

      The absolute permittivity is the relative permittivity multiplied by the absolute permittivity of a vacuum, 8.85418781… x 10^-12 F/m.

  9. Have done this experimentally with paper and foil. I wonder if the plastic wrap isn’t easy to pierce. I think paper would stand up to tighter rolling. The smaller the gap between your capacitive plates, the higher the capacitance. Fun experiment. Hook it into a 555 timer or op-amp relaxation oscillator and try for the lowest frequency! Try oiling your paper to see if that changes your capacitance value.

  10. I did this many years ago when I was building a tesla coil. It was of the plate variety using aluminum plates, polyethylene sheets and oil. Although air bubbles between plates equals internal arcing and one big oil covered mess. Have also seen beer bottles and salt water used. Ahh memories of things that could have killed me..

    1. Better shielding. Unrolling them greatly improves their performance as sensors, and will reduce the predictability of the circuit it is in. And makes them take up a ~lot~ more room.

  11. I’m experimenting with different types of capacitors and if they can replace batteries voltage-wise, economics-wise, and environment-wise for my science fair and I made this. It didn’t generate that much but it was fun to make XD

  12. Your multi-meter probably didn’t include a “capacitance” range. A slightly more expensive multi-meter that would have this capability would be informative. It would have allowed a measurement of the capacitance in pico-farads. This way one can get an actual measurement of what you are attempting to make. Comparison of different construction methods, including the size of plates, etc is easily compared this way.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s