Can aluminum foil store electricity

Answer 1

The answer is YES. One can build an energy storage capacitor, using aluminum foil and a suitable insulator, in the comfort of one's own kitchen.

The following essay is provided based on my analysis of this question several decades ago, early on in my career as an electrical engineer. The cost estimates which I used for the concluding paragraphs were based on prices available at the time; but times change, so things might pencil out differently today; I'll leave that to someone else.

I designed a large storage capacitor using aluminum foil and mylar film used for preserving food in the refrigerator.

The amount of VOLTAGE that can be applied to this storage device is strictly limited by the characteristics of the insulating material. Newspaper could work. Wax paper is better than newspaper. And Mylar is better than wax paper. All three of these can be used to build a quick and dirty storage device in the comfort of your own living room. Mylar, as available on a household roll from the supermarket, can handle a lot more than 12 volts. Wax paper has been used in the distant past for very low power applications. Newspaper has never been used, to my knowledge.

I cut all the sheets in a square format, roughly 1 foot square using the materials I found in the kitchen cupboard, with the mylar squares being just enough larger than the aluminum squares that every aluminum square will be definitely and positively separated from its neighbor sheets. This is important.

The wife spotted me and I had to make an emergency trip to the grocery for replacements. This is important, too.

I started placing the sheets in the following pattern:

One sheet of insulator

One sheet of aluminum foil, offset to the left about 1/4 inch so that it was slightly exposed;

One sheet of insulator

One sheet of aluminum foil offset to the right

One sheet of insulator

One sheet of aluminum foil offset to the left

...and so on, repeating that procedure.

All the exposed aluminum edges on the left are connected together electrically. and all the exposed aluminum edges on the right are connected electrically. One side is meant to be connected to the positive electrode and the other to the negative electrode. Doesn't matter which; just don't accidentally touch the two together.

Charge it up to twelve volts, and it will take and hold that charge for quite a long time. Connect it to a (12 volt) device that uses minimal current, such as a small radio or an LED light, and it could power that device for quite a while.

It behaves in every way like a battery. It is charged up using DC (Direct Current) electricity, and its energy is fed out to DC devices only.

CAUTION: This device will NOT store AC (Alternating Current) electricity. This will make the circuit breaker out in the garage go pop, and you will have to go find it to turn it back on again. DO NOT connect this device to a wall socket.

Using DC, a larger pile of sheets will store commensurately more electricity.

Theoretically, one could build one of these things without limit.

However, there is a certain hazard, and the risk from this hazard can be devastating. I never went beyond designing a modest storage device, because of the risk of having anything larger. Here's what I mean by THE HAZARD:

None of these insulating materials were produced with the idea of storing electricity. So from an electrical point of view, the insulating properties of each of these materials is variable. The thickness is variable, and there may be tiny holes. Newspaper will show the most variation. Wax paper will be slightly better in this regard, as the wax fills in the weak spots somewhat. Mylar will be best ... but there are still variations, not only in thickness but in the occasional tiny hole, too small to see.

Consider this scenario: You and your friends decide to build a GREAT BIG storage device in your buddy's garage. You plan to use it to jump start vehicles which have dead batteries, without having to wait around while the vehicle battery gets enough charge to help out. You want to make it start NOW, so you want a big storage device.

You get hold of the cardboard carton that once held his new refrigerator and you start building an enormous storage capacitor. You place it in the garage, in between the wife's SUV and the riding lawn mower.

After several weeks of cutting sheets, laying them out, going to the grocery for more aluminum foil, more mylar and more beer, finally everything checks out and you start charging it up. One of you plugs in the battery charger. The battery charger makes a complaining noise and pops its little safety circuit breaker.

This has never happened before, but every time you reset it and try it again, it pops again. Eventually one of you puts down the beer can and digs out the instruction manual for the battery charger. You discover that this charger has a safety feature that detects a short circuit, such as when your 5-year-old hooks the leads together. This is to keep the battery charger from burning itself up.

The storage capacitor looks like a short circuit to the battery charger, at least at the first. Once some charge has built up, then the current requirement will drop and the battery charger will be able to handle the job.

Gotta limit the current flow.

Eventually someone thinks of the idea of including some form of resistance to put into the charging circuit. After several unsuccessful tries, one of you finds a spare headlight bulb with one working filament, and hooks that in series. The battery charger is capable of pushing current through the headlight bulb without popping its circuit breaker, and doesn't even know that the storage capacitor is there. The storage capacitor happily begins storing up energy.

Two or three days go by and eventually you notice that the headlight bulb is getting dimmer. This means that the current flow is slowing down. This is normal. It means, in turn, that the voltage which has built up in the storage capacitor is now at some respectable percentage of the capacity of the battery charger. A voltage meter (DC) applied to the storage capacitor will probably show that it is around 4 or 5 volts now.

Depending on the capacity of the battery charger, it will be desirable to remove the light bulb from the circuit and connect the battery charger directly across the storage capacitor. The battery charger hums loudly, and the voltage meter shows that the voltage is slowly building up.

You plan for the moment when you can disconnect the charger and provide a demonstration of the power of this device. You decide to use your kid's pickup, which has been sitting dormant in the street for weeks because he can't afford a new battery. You push it into the garage, in front of the storage capacitor, and lay out the jumper cables.

Next Saturday comes. The guys all arrive with beer and families and prepare to see the storage battery begin to do its work. A small crowd arrives at the driveway in front of the garage. They are just about ready to open the garage door to inspect the storage capacitor at full readiness, and shut off the charger ... when something unexpected happens.

There is a pop, immediately followed by a BANG, and the garage door is tossed out in front of the garage. Smoke and flames billow out, a wave of heat hits everyone with enough force and heat energy to curl the hair of the closest bystanders. The inside of the garage is totally engulfed in flames. Every container of gasoline (such as the gas tank in the pickup, in the lawn mower, and in the wife's SUV) is totally on fire and busily destroying everything around it.

We won't go into the visits by the fire department, the insurance investigator and the contractor hired to rebuild the front half of the house. Let's cut to the chase: What happened?

Somewhere inside of that storage capacitor, a weak point in the mylar insulation allowed a tiny trickle of current to get through. It wasn't much, but it was just enough for the current to build up a bit of heat. This hot spot began melting the mylar from a solid to a liquid, and when the liquid got hot enough to turn into vapor, it made a hot bubble ... the pop ... and escaped from the capacitor as a gas, like air leaving a popped balloon.

Then the two opposing aluminum sheets came together and made positive contact.

The stored energy developed an enormous instantaneous short circuit entirely within the storage capacity ALL AT ONCE, and ALL IN THE SAME PLACE. That produced an enormous amount of heat ... nearly instantaneously ... and vaporized chemicals from the mylar, which made a flammable gas, which ignited, thus producing the BANG, which spread the heat, which ignited everything around it (the interior of the garage).

The mylar sheets are good for a hundred volts DC or more. Twelve volts is an eighth of that. So why did it happen?

It's because the household mylar sheets were never designed to hold back electricity; they were designed to hold back microbes, and air molecules. And the household mylar does this just fine. But every now and then there is the tiniest imperfection, much smaller than the size of an air molecule ... yet it's big enough to let electrons through.

There aren't many imperfections like that.

But all it takes is one.

Caution Notice: Don't use household materials for purposes for which they were never designed. Not without a very large safety factor.

OK, so now I'll back away from giving the caution notice, and give a bit of advice.

If you've gotta have an electrical storage device for the kid's science fair project, and you've gotta have it TOMORROW, and Radio Shack is closed, then go ahead and build a small storage capacitor as described above. Choose a demonstration such as a light bulb that runs on low voltage and requires low amperage. LEDs are much better than light bulbs using a filament.

Next, what if you really do want to make a really big storage device?

Advice: Stack the odds in your favor: Use two sheets of mylar in between every sheet of aluminum.

Up side: Your safety factor just went up by a huge amount.

Down side: The storage capacity of your device just went down. (Because the aluminum sheets are now twice as far apart, and this decreases the storage capacity.)

As a science fair project, this is a good, fun thing to build.

If you want a rugged, reliable and safe storage device for your home for permanent use, use large size capacitors from Radio Shack. These are all designed by the best engineers to use the thinnest mylar films, made to stringent standards, with the minimum of aluminum films, resulting in devices which have a remarkable amount of energy storage for their size. They can be connected in a series-and-parallel arrangement to give considerable power storage capacity. Safely. Except for the risk from the do-it-yourself connections. All it takes is one unwanted cross-connection and everything will go up in flames before you can say"Oh! No!"

Yet, even here, there is a safety factor in comparison with the do-it-yourself aluminum foil and mylar; because every commercial capacitor is encased in a capsule which gives considerable protection from the smoke-and-flames scenario described above.

When you do the calculations, be sure to compare the total cost (aluminum foil, mylar sheets, soldering equipment and BEER) to the cost of a deep-cycle (RV-type) lead-acid battery. When I did that, years ago, I found that it was MUCH less expensive to go with the battery. Holds more energy, in a smaller package, for LOTS less money, LOTS less risk...

And LOTS less beer.

Morry