Homemade Capacitor

[Anon_LG]

I can give very little information about this project as it is for the Google science fair, so I can not reveal the reason that I require this information.

Does anyone have any suggestions for a high relative permittivity material, available in thin sheets, that can either be bought online or would be accessible within my home. I need to make a > 1 Farad capacitor in under about 2m^2, needs to have a breakdown voltage of above about 40 volts (will be charged with roughly this many volts across the plates) and needs to have an effectively indefinite lifetime. The dielectric material must be a solid. I am operating under the capacitance equation:

Yes I have done my research, no I not going to kill myself.

I plan to use aluminium foil (kitchen foil) to make up the plates, using two plastic plates either side, screwed together, to keep the plates in contact with the dielectric in compression. Will the idea of using aluminium foil for the plates work?

This appears rather strange upon re-reading, however I have run out of ideas for the dielectric material.

 

[Arouse1973]

Mylar may work
Thanks
Adam

 

[Anon_LG]

Thankyou for the suggestion Adam, however I have just done the equation, in order to get any where near the desired value I required this:
3.1 * electric constant * ( 2m^2 / 0.0000000001 metres) = 0.55 farads
The situation is dire, the required thickness, 0.0000000001 metres, is one angstrom, about the width of an atom.

The realistic substitutions : 3.1 * electric constant * ( 2m^2 / 0.000001 metres) * 40 volts ^ 2 = 2.2 milijoules
that is at 1 micron thick, I require joules.

I am beginning to highly doubt the likelihood of build a home made ultracapacitor, I will continue researching and hoping for forum advice until I either build one or have checked every realistic possibility.

Thanks,

 

[Arouse1973]

The only other thing that will work is Graphine coated insulators, good luck with that. I work with a student that made one as a uni project. Dont know what capacitance it was. Cant you just purchase one?
Adam

 

[hevans1944]

Nanoparticles of charcoal offer your best hope of constructing an ultracapacitor with more than one farad of capacitance. Good luck with that. I have a attached a file explaining how one company manufactures ultracapacitors using activated carbon particles. You would need to place about fifteen well-matched capacitors in series, each capable of about 2.7 WVDC, to obtain 40 WVDC. And of course each ultracapacitor would need at least fifteen farads of capacitance, since they are in series, to reach one farad total capacitance.

 

[Osmium]

Thinking in 3 dimensions, if you have alternate layers of foil and food wrap connecting every odd numbered "plate" as one side of the capacitor and the evens as the other side, what does a 2m cube give you? Apart from a hernia trying to lift it...

Alternatively, a 200m roll of food wrap sandwiched between 2 x 200m rolls of foil and rolled?

 

[hevans1944]

Thinking in 3 dimensions, if you have alternate layers of foil and food wrap connecting every odd numbered "plate" as one side of the capacitor and the evens as the other side, what does a 2m cube give you? Apart from a hernia trying to lift it...

Alternatively, a 200m roll of food wrap sandwiched between 2 x 200m rolls of foil and rolled?

@Lavaguava in post #1 provided the formula for calculating capacitance. Plug and chug.

 

[Anon_LG]

Cling film. I did not think of that. It appears that using plastic wrap would be rather effective compared to other substances, the equation taking into account the relative permittivity of 4, and 200 m^2 of plate and dielectric.

4 * electric constant * (200 m^2 / 1.25 × 10^-5 metres) * 40 volts ^ 2 = 22.67 milijoules

*Cries*

Will this torture never end, maybe a hydrogen fuel cell is the way forward...

Thankyou for the help,

 

[Laplace]

Will this torture never end...

One more flogging......Consider that whatever you can create in your kitchen will not have the volumetric efficiency of a commercial polyester film capacitor. So choose an appropriate film capacitor, determine how many would be necessary to satisfy your farad capacity needs, then arrange them into a cube form. What is the volume and weight of that cube? Whatever you make will be larger.

 

[BobK]

If he is going to do that why just buy a 1F capacitor?

Bob

 

[AnalogKid]

>1F is an enormous amount of charge, up in the trick question range. There probably is one material that is available and has the right properties, and unless you figure that out you're sunk. This kind of test is more about the superiority of the questioner than teaching.

Moving on, cheap kitchen storage film and aluminum foil are thinner than the brand names. Both have the thickness on the box, so get the thinnest stuff you can find. Make sure the film is wider than the foil (might have to trim the foil). Foil/film, roll as tightly as possible starting with the foil on the inside. Then measure it and see what you get. The capacitance will be higher than the area calculation because of the interaction between layers.

ak

 

[hevans1944]

>1F is an enormous amount of charge, up in the trick question range. There probably is one material that is available and has the right properties, and unless you figure that out you're sunk. This kind of test is more about the superiority of the questioner than teaching.

One farad is an enormous amount of capacitance. Charge is what you put on it, electrically, and can be any value up to where the capacitor fails by arcing through the dielectric. Q (charge) equals C (capacitance) multiplied by V (voltage across the capacitor): Q = CV.

... Moving on, cheap kitchen storage film and aluminum foil are thinner than the brand names. Both have the thickness on the box, so get the thinnest stuff you can find. Make sure the film is wider than the foil (might have to trim the foil). Foil/film, roll as tightly as possible starting with the foil on the inside.

That's good advice on how to make a capacitor, but be aware it will require a LOT of film and foil to reach one farad.

... Then measure it and see what you get. The capacitance will be higher than the area calculation because of the interaction between layers. ...

.
No it won't. There is only one layer. Whether it is rolled up or laid flat on a football field makes no difference. The only things that makes a difference is the area, the separation between the two layers of foil, and the dielectric constant of the film. The OP posted the formula for calculating capacitance of a parallel plate capacitor.

 

[AnalogKid]

Yeah, my fingers got ahead of my brain, twice. As for the amount of film, that was my point. Way too big a requirement to teach anything useful.

ak

 

[hevans1944]

... As for the amount of film, that was my point. Way too big a requirement to teach anything useful. ...

The requirement was self-imposed. @Lavaguava is doing this (or at least trying to do this) as part of an entry to the 2015 Google Science Fair, which entries closed early in May of this year for the 2015 world-wide competition. Regional winners will be announced in July. Well, if @Lavaguava and possible team-mates don't win this year, maybe they will still be young enough to enter next year if technology has advanced enough to allow home-built farad-sized capacitors in the forty volt range. If they can do that, I would take the money and run... anywhere that suited my zillionaire fancy. One can but hope that tech will keep up with our dreams, lest we are forced to wake up and invent it ourselves. A lot of progress has been made that way.

As for my dreams (even though no one asked): I have been waiting at least forty years for Hollywood to resurrect with CGI my favorite movie actors so they can do their stuff on the big silver screen again. As in, "Well, Pilgrim, are you gonna use that blaster or talk those aliens to death?" Yee Hah! Yippee ki-yay, rubber plucker! (Ooops! He's still making RIM [Retirement Investment Movie] films. The latest one I've rented was the 2013 film "The Prince" with John Cusack, also into RIM films now, which I thought decent if not memorable.) Really looking forward to Marvel's new films as soon as they appear on Blu-Ray disks. If I can't have CGI actors, at least I can have CGI everything else.

 

[Anon_LG]

Luckily I have a few years left of possible entry, I am 14 so there are three more potential years ahead. After careful review of all the options (I have done quite a few hours of research), I believe that I should focus my efforts on a hydrogen fuel cell based project, however as with the capacitor, the hydrogen cell will only one part of the project. I am still researching capacitors, as you have said @hevans1944 , the technology is advancing.

My deluded vision of a dielectric with a suitably high relative permittivity, under my stated requirements, is looking like a broken dream now (at least with current materials technology...). This thread is very interesting to follow, I did not expect to recieve so many replies (with possibly more on the way), if anyone can deliver that miracle answer then the supercapacitor is back in use. I will not stop until I have found built a full working super capacitor (and the rest) or a full working fuel cell/s (and the rest).

Your advice is very much appreciated,

 

[hevans1944]

@Lavaguava Hydrogen fuel cells have been used for years by NASA to power outer space Earth orbit and Moon excursions. They have the advantage of producing only water (which can be re-cycled for human consumption) when the hydrogen fuel is "burned" (oxidized) in the fuel cell. They will probably be used in future manned missions to Mars and the planetoids of the asteroid belt and the moons of the gas giants, Saturn, Neptune, and Jupiter. A man's gotta have water to survive!

The downside is hydrogen is difficult to handle and store. In gaseous form it has an explosive concentration range of something like four to ninety-nine percent when diluted with oxygen or air... a wider range than any other combustible gas. The public is still wary of hydrogen, remembering the Hindenburg disaster. Right now, the only practical way to store hydrogen for use in a fuel cell is as a cryogenic liquid (NASA's method) but there is a lot of research on storage based on binding the hydrogen atom with other things, either chemically (as a hydride for example), or mechanically in the pores of a hydrogen "sponge" material. The latter is promising since a huge surface to volume ratio can be achieved with nano materials.

The biggest problem facing commercial use of hydrogen fuel cells (after the storage and safe handling problems are economically solved) is where do you obtain cheap hydrogen? Separating hydrogen electrolytically from water using electricity is a non-starter because of the inefficiency of the energy supply chain. Perhaps if it is done with solar-generated electricity it might eventually "break even" but the data so far is not encouraging. A break-through design in photo-voltaic solar panels is needed, something equivalent to a cheap spray-on coating of an inexpensive substrate (think glass, or steel, or aluminum) that offers at least ten or fifteen percent conversion efficiency at a cost of a few cents per kilowatt of energy harvested from the Sun. There is always maintenance and energy deliver cost to consider too, so capital investment in generation capacity is just a small part of the overall picture.

Quite a few years ago someone was demonstrating photo-chemical dissociation of hydrogen from water, using a type of algae IIRC. Haven't heard anything about it since then, but you might want to do a Google search to find out what the current state of the art is. I have attached an interesting paper from India to get you started.

It is encouraging to hear that our youths are working on the "energy problem". After all, cheap hydrogen fusion generators are always fifty years in the future, and have been for almost a hundred years since the atom bomb was invented. The only working fusion reactor the human race can use for power right now is the Sun, parked a safe 93,000,000 miles away with hard vacuum between it and us to transmit its broad-spectrum radiation and charged particles (protons, mostly) to Earth. We should be using it more than we do, and not just for global warming, although that is essential for human survival. It would get mighty cold here pretty quickly if the Sun were to vanish. Just ask the outer planets about that.

Hop

 

[Anon_LG]

Agreed, safe storage of hydrogen is a major problem. I will however be storing only a few litres of hydrogen gas at most, I understand that there is a risk, one that I am wiling to take. The sponge idea sounds interesting, I will research this further. Obtaining the hydrogen will be no problem.

I would like to provide more information however I run the risk of having the idea taken. Thanks for the great advice,