Old School High Voltage Capacitance

What would MacGyver do if he needed a high voltage capacitor but only had some foil, tape, water, salt, a nail and a plastic jug?  He would build a salt water Leyden jar, that’s what.  The Leyden jar is a very simple capacitor. Invented in 1745, it has been integral to many scientific experiments. Check the wikipedia entry to learn more about the history.

This specific type is quite easy to make. It uses a salt water interior instead of foil on the inside and outside. That means you could slap one of these together in a few minutes to impress your friends and/or electrocute yourself accidentally.  Please be careful as this is high voltage.

29 thoughts on “Old School High Voltage Capacitance

  1. This is not a hack, but at least its
    something new on high voltage on this site

    Can we get some crazy impossible hacks like a pic running linux or something??

    Also, you guys used to be so awesome with your hacks, but now its just simple diy type of things :T

  2. Eh, kinda neat, but Hak8or is right, not exactly a hack… On the other hand, it’s not like you can just snap your fingers and a genius puts linux on a pic. Think about it, a pic has so little processor capability compared to most things that run linux.

  3. @ bob. you could have phrased it better but i can understand the sentiment
    unfortunately there will always be trolls that can’t handle the slightest changes on hackaday

    funky hack though :) now i just need to figure out something really dumb to do with it ;)

  4. Honestly though guys your expectations are a bit lofty. Hack a day is a WONDERFUL resource for those hacks and projects that come out, are documented enough to provide a thoughtful and insightful article, and are also new and ground breaking. Only so many good advances can come to the surface if there is no fresh input. The best solution to your concerns: Get out there with your soldiering irons, pic programmers, tools, and what ever know how that you’ve picked up or are able to teach yourself and get inventing. The ONLY solution to that which you are complaining about is a lack of fresh material. So instead of just griping, be proactive.

  5. I’ve long thought of making a simple axial capacitor from two rolls of tinfoil, and two rolls of wax paper (or saran wrap) interleaved and rolled up tight.

    It would be easy enough to measure the capacitance, but you’d destroy it the moment you found the maximum working voltage.

  6. @almost_there

    You could make a guess as to the maximum voltage of the Capacitor by examining the dielectric strength of your unit, wax paper. If you worked under half of that (possibly more, but half is a good start), that would be a good maximum working voltage.

  7. while the “standards for entry” have certainly decreased a bit as compared to the former hackaday, i’m not complaining. although all of the articles may not be “how to get linux running on a pic” grade hacks, most of them (like this homemade capacitor) are at least mildly interesting, and give me something to read when i am looking for a distraction from my work. :) and as others have said, if it’s so easy to get your project featured on hackaday now that there are more people here to post them, then what’s stopping you from being the one to share the next awesome hack. seriously, if you know how to run linux on a pic (or better yet, a single vacuum tub), by all means share. but until then, no whining.

  8. The rolled aluminum foil/waxed paper design is a good start, but it would work much better with a few improvements.

    First, to keep it from arcing over on the edges at (relatively)low voltages, you need to stat by cutting down the aluminum foil. Just use hacksaw/bandsaw/etc on the bare role of foil. The next improvement would be to switch to some type of plastic over the waxed paper (its a much better dieletric, so you will store considerably more energy in your capacitor, and it is available in a much wider range of thickness so you can design a cap for any voltage you want). If you wanted to stick with kitchen supplies cling/plastic wrap, although your max voltage would be limited (but if you made a cap out of a whole role of Al foil/cling wrap you would probably have 100nf-1uf of capacitance!). Better would be painters plastic (made out of hdpe) sized for whatever voltage you want, 500v per mill of thickness (best to make the cap good for about 2x the voltage you plan to use so it will last a while). Over about 10kv you will run into corona problems, so you have to dunk the cap in oil to take care of that.

  9. almost_there: You can use two layers of tin foil and ceran wrap in between. (paper clips for the hook up).

    Don’t roll it up though, hang it up flat, the voltage will pull the layers tight.

    And, to some extent it is self healing, a couple sparks through the ceran wrap won’t kill it but evaporate enough aluminum to keep it insulated.

    Just as a warning: Capacitance goes up with surface but also with 1/distance of the plates. Since ceran wrap is very thin, the foil plates can hold quite a charge. It is not safe to touch!

  10. I think the reason for lots of Digg/Instructables/&c stuff getting posted is /that’s where the hacks are going!/

    In the ‘good old days’ folks would use their college/uni.ac or .edu/~[name]/projects.html to host their stuff, then wait for it to be picked up on by (for example…) Hackaday!

    Now, they’re hosted on instructables and/or dugg before hackaday gets to them.

    I have to agree – at least in part – that the (subjective) quality of submitted hacks has dropped, but that’ll be mostly a function of sheer numbers due to accessibility, like working your way through the dross on deviantart.

    [pithy conclusion here]

  11. also something that should be considered is th fact that there just aren’t that many hardcore hacks these days that aren’t on some ones private blog or dig or engadget.its hard to find deacent hacks so they have to use filler until the good stuff comes along

  12. the only things annoying about h-a-d are the trolls. maybe they would prefer “hack a once in a while” or “hack whenever i get around to it” so that we can wait for the great hacks to come along.

  13. How is DIY not a hackish topic?
    I mean… DIY is doing that with what is not contemporary of the present time period; hacks are in the same vein.
    DIY is like… hacking nature… or… not relying on a corporate entity to big brother you through life.
    A hack is like… hacking consumecr products… or… not relying on a corporate entity to tell you what is and is not possible to do with one of their products.
    Seem similar to me… and this kind of diy project could even be used in a pic controlled hack project, charged by electrostatic energy, stored in these jars… or something.

    I agree that it’s better than product placement ads of other sites.

    An African Swallow or a European Swallow?

  14. I saw a show about some German students who made a Hydrogen fuel-cell powered go-kart and they used large (commercially made) caps to make up for the low current output capability of the F.C.

    This and other homemade condensor designs (yeah, I’m old-skool ;) have great worth in DIY alternative energy/transportation applications (ie. “hacks”).

  15. It’s wholly ironic that the trolls who come here to complain about the lack of ‘hacks’ are the ones that have never done anything original in their life. hack8tor, yoshi, pip: let’s see what you’ve contributed over the last 12 months.

  16. As a non-hacker who is interested in technology old and new, this site is great fun and informative to view. I might not want want to learn how to run linux on a pic should such a thing ever become possible, but you must remember that this kind of article is inspiring for people like me. Keep up the good work Hackaday.

  17. I like this as it puts things in perspective. if you don’t know where you came from, you’ll never understand where you’re headed. Plus, it makes a nice project for somebody that doesn’t want to spend lots of time and money on something much more complex that is equally impractical.

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