I've recently been trying to create a capacitor at home. Capacitors store charge on opposite sides of two parallel plates that have some kind of dielectric material between them. The dielectric material can be air or another substance with a higher dielectric constant. Here is a diagram of a capacitor:
Now I've found some tutorials online that show how to make some, and it looks pretty easy. However, most of these capacitors are only in the high picoFarad to low nanoFarad range, and for the rail gun project, I'll need capacitors that are in the microFarad (uF) range. Most of these homemade capacitors used designs where two aluminum foil sheets are separated by a piece of paper or tape. I found a video on YouTube, however, that details the construction of an electrolytic capacitor:
(from yt/RimstarOrg)
These capacitors are still simple to make, and they can have values of capacitance well into the uF range. Capacitance can be given by this formula:
So if you want to increase capacitance, you should have your dielectric, which sits in between the plates, to be very small, as this will decrease your d (distance) in the denominator. An electrolytic capacitor makes this easy since the dielectric layer is essentially a very thin layer of aluminum oxide that is produced when you induce a voltage into the electrolyte solution (baking soda and water) with two aluminum plates. I thought about using soda cans like in Rimstar's video, but I couldn't find an easy way to refine them into plates. I figured using aluminum foil would be a lot better anyway since it's much easier to get a lot of and to shape. The piece of foil that will develop the oxidized layer should be made large since this will increase your A (area), which is in the numerator of the capacitance equation. This piece will also be known as the anode and will be connected to the positive lead. You can see here how I cut out the anode from a larger sheet pressed flat, which you can do with a ruler or heavy book. I also gave it a protruding section where I could connect the positive wire.
(the anode I've cut here is roughly 44cmx8cm)
Next, I got to work on curling it up so it could fit into my container. I used a highlighter to help me roll it up. After that, I used a ruler to slide into the rolled column and expand it to make the distance between the foil larger so that the aluminum didn't make contact with itself.
I placed the foil from the second image into a random jar I found in my house, and then placed a thin piece of aluminum for the negative lead to connect to. I poured in some water and added a few tablespoons of baking soda. Then, I connected the jar capacitor to a double-A battery to start the oxidation.
I left it going for a bit, then switched the battery to a 9V and left it for a few hours. I also added some more baking soda. This method can definitely be improved upon. For example, I could've made a baking soda solution, mixed it before adding it into the jar, and then placed the aluminum inside. Instead, I poured in the powder last and then had to wait for it to dissolve without shaking it because I didn't want to disturb the aluminum foil structure I had already placed inside. Obvious improvements like this, as well as others, will be implemented in the next post I make on this, so that a suitable capacitance is available for the rail gun project.
I ended up reaching a maximum capacitance of around 1.4 mF or 1,400 uF. However, my multimeter's readings were showing high variation, and it would also drop to around 800 uF as well. This variance might've been from the fact that I don't have clip-on leads to connect with, so I was using my hands the best I could. I'd also gotten open load readings a few times, but I was able to fix this by adding more baking soda. My current theory for why that happened is that after using the baking soda to oxidize the aluminum, too much is used up, and there's not enough to act as an electrolyte for the solution. Here are some of the readings:
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