I decided to try making one for a fun project and I'm having some real struggles.
Some squares of foil. paper towel. and distilled water with baking soda mixture. I only added a little over a pinch. into about half an ounce of water.
Since its so small. I put it in a sandwich bag. rolled it up and taped it.

I went for a goal of a 16v one and began slowly charging it up with a 100mA current limit but it took so long for the voltage to climb up to 16v. and it was even getting a little warm at some point.
I had to repeatedly turn it off waiting for it to cool down. then try again.
After so many hours the current eventually fell to 8.9mA but thats still way too high to hold a charge on it's own. it drains in a half a second to only 0.5 to 0.8v
I tested it though and it seems to function. I see a small spark on the alligator clip when hooking it up to my 16v source but it drains away in only a second

There seems to be some kind of breakdown happening around 0.5 to 0.6v where past that it wants to discharge rapidly. at somewhere around a few milliamps

Could my distilled water or baking soda be contaminated?
Or the aluminum foil itself?
I tried different brands and types of paper towels and even plain printer paper. and had the same result.

if I try it with just a couple small pieces in a clean glass jar with no paper or anything it seems to not have that issue. and the charge forms almost imediately.
What could I be missing? Am I just doing it wrong? Do I need to be even more careful about contamination and use gloves for the entire process. from grocery store to finished assembly?

The current its drawing is still decreasing but at a very slow rate. Takes hours. almost an hour per milliamp of current drop.
by this rate it could take multiple days of forming for it to reach a very low level of a few micro-amps of self discharge.

 

Your experiment appears to be electrolysis, not charging a capacitor.

 

No Water, and No Baking-Soda.
Either one will simply short-out the system.

You might be able to create a crude Battery this way with the use of some dissimilar Metals,
but it will never be a Capacitor using Water and Baking-Soda.

Use Toilet-Paper only, but don't expect very much Capacitance.
It would be really impressive if You got 1-Microfarad out of it.

A small Capacitor will Charge faster than You can measure.
It will also Discharge faster than You can measure.
.
.
.

 

How do I get a suitable electrolyte then? without it I just get an open circuit and no appreciable capacitance at all. smaller than 1 pico farad.
its drawing 7.4mA at 16v right now.. so not much of anything is happening and its still dropping slowly.
I find several tutorials about doing it like this or something very similar with distilled water and baking soda or some other additive to make an electrolyte solution.
Can I get a safe non-dangerous electrolyte solution to make my capacitor work instead of baking soda and distilled water? I have some very thin toilet paper but Its so much more fragile than paper towel or printer paper it'd disintegrate on contact with water.

it takes about 0.7-1 second to drop from 16v to 1v. with the 7.4mA of leakage.
I saw someone else get it working enough to flash an LED but I can't seem to replicate their result.
How come it works so much better with just 2 foil pieces in a jar or glass of water. with no paper insulator separator? I don't get much capacitance but the leakage current is miniscule

 

It's not practical for You to create a DIY, real "Electrolytic" Capacitor.
You can create various other Capacitor designs using various insulating materials, even just plain Air,
but it will be massively-huge in comparison to a manufactured Capacitor of similar ratings,
and is not likely to last very long before some kind of failure occurs.
.
.
.

 

Thats disappointing darn. I really wanted it to work.

 

Making your own electrolytic capacitor is doable, but challenging. If you are just doing it to see if you can do it, that's fine. If you are actually thinking of using it for something, you should probably walk away now.

Start small. Don't try to make a rolled up capacitor, try to make a small parallel plate capacitor. Using, say, two 3"x5" pieces of aluminum foil, lay one down on the bottom of a glass baking tray, put down your paper towel and electrolyte solution, leaving about 1" of the short edge exposed, the lay the other down on top of the paper towel, leaving about 1" having off the other side. These are your contacts. You might put a flat-bottomed glass on top of the stack to hold it down.

By keeping it small, it should be pretty obvious if you have a short, since the forming current should be pretty tame.

One thing to keep in mind is that the oxide formed by this method degenerates pretty quickly, so every time you use it you will likely have to reform the oxide layer almost from scratch. Another reason that this is really only suitable as a demo to show that it can be done.

 

Would boric acid or baking soda be a better electrolyte solution? Any reason one would be better than the other?
I know baking soda is pretty much the safest out of anything imaginable.
Its just an experiment for fun and finding stuff out for myself.
Plans would be a sandwich baggy. two squares or rectangles of heavy duty kitchen foil. paper towel in between. layed flat. and the electrolyte solution poured in.
So quite small scale.
How would I minimize every possibility of excessive leakage current? any potential sources of contamination or anything?
Does the leakage current improve the longer I keep the capacitor charged and the more i use it?
Do I just need more industrial/pure grade ingrediants to reduce leakage? more ideal neutral and clean separator insulator material. foil. and electrolyte?

 

To form an electrolytic capacitor the process includes forming a non-conducting oxide layer, which is a complex process.
You can produce a capacitor with aluminum foil and either wax paper or that thin plastic wrap. It will take a few layers and a means to gently press the sandwich flat. You will have more success but less capacitance.

How did you come across the recipe for your first effort? What claims were made for it?

 

Capacitor electrodes need to be separated by a dielectric material.

 

Try forming the capacitor at a lower current for a much longer time, like several days. Keeping the current low should prevent overheating.

 

Given the actual construction of electrolytic capacitors, it seems that the concentration of whatever is used to form the insulating layer should be much greater.
This project smells a lot like one of the faked yootoob postings that do not actually perform as claimed.

 

Given the actual construction of electrolytic capacitors, it seems that the concentration of whatever is used to form the insulating layer should be much greater.
This project smells a lot like one of the faked yootoob postings that do not actually perform as claimed.

The concentration of the baking soda is supposed to be saturated -- you keep dissolving it in the water until it won't take any more.

As a proof of concept demo, the project can work. I haven't done it personally, but I have a few friends that are much more into that kind of stuff and they have been successful -- after a fashion.

 

Capacitor electrodes need to be separated by a dielectric material.

The dielectric is a thin oxide that electrolytically forms on the aluminum foil.

 

Back in post #1 we see that there was not close toa strong enough solution to have much effect. AND, not mentioned at all, the roll has to be TIGHT, with the paper towel compressed between the foil layers.A loose wrap will only have a small portion in contact even if everything is correct. Did any instructions even mention that???

 

I tried that way already before. but it heated up and had very high leakage current even after many hours of waiting and trying to form it.
with saturated solution.

 

The diaelectric is aluminum oxide which forms on the surface of the aluminum. This can be disolved by bases which include baking soda (usually demonstrated with sodium hydroxide):

https://chemistry.stackexchange.com/questions/7119/corrosion-of-aluminum-by-baking-soda

here's a table which might give you a hint a a better eletrolyte to use:

https://en.wikipedia.org/wiki/Electrolytic_capacitor

 

Back in the days when transistors were carved out of wood, we would sometimes have for re-form old aluminum electrolytic capacitor, but would often have have a series resistor. You are tying to anodize a bit of aluminum, and that can be a very low resistance load (as a former anodizer)

 

So would borax/glycol mixture be more suitable? Without causing the breakdown effect problem with the huge leakage current?
How safe are those? Are they immediately dangerous or harmful if you accidentally get a little on you?

I found out just putting two sheets in a container layed flat and not rolled up works very good at having low leakage current. but the capacitance is small. No pinholes are visible with a bright light shining behind the sheets of foil. so they aren't degrading as fast.
Actually they hold voltage quite well infact. holding over 10v when charged to 15v for at least several seconds while very slowly and gradually dropping.
it actually works like this and flashes an LED very brightly.

 

I did even more experimenting and seems my separator paper is too thin and I need to tripple layer it to ensure theres no breakdown occurring between the plates. Too close and the plates just breakdown current between them. too much is just lower capacitance.
Also need to keep the current as low as possible. with a resistor or something.
I got such a great result with the plates just in a container because the separation of the plates was very large. so very low leakage current even up to 16v. with lower capacitance. still enough to flash an LED!