The brief history and technology in capacitors by Jeri Ellsworth, this is part of our A – Z of electronics series we’ve teamed up with Jeri to do! You can view A and B here!

Capacitors, or also known as condensers, are devices that store an electric charge between two parallel metal plates. The plates are separated by a gap or a non-conductive dielectric material.

Although friction methods of producing electric charges have been known for thousands of years, there was no method of storing or accumulating charges for extended periods of time. In 1745, it was commonly believed that electricity was a fluid, and the German experimenter Von Kleist was convinced he could lead electric fluid from his generator and fill a bottle with it. During one of his experiments, he discovered that filling a bottle with a liquid such as water or mercury, placing a wire down the neck, and touching the wire with a friction generator would store an electric charge, but only if he held the bottle. He could carry the bottle around for hours, and from room to room, and still pull a large enough spark to ignite alcohol or cause painful shocks.

Eager to share his discoveries, he wrote to the leading scientists around Europe describing his experiments. In one letter, he warns, “I would not take a second shock for the kingdom of France.” Kleist was not well-known or respected, so those who received this letter did not manage or care to recreate his claims.

The following year, a Dutch scientist, Pieter Musschenbroek independently made the same discovery accidentally while trying to measure the strength of electricity with a suspended gun barrel and a brass wire extending into a jar of water which he held in his hand. To his surprise, he received a strong shock from the jar, which made him believe that he was done for. After further experimenting, he found that metal on the outside of the jar could take place for his hand.

Because of his reputation as a teacher, the science community took notice, and his device was named the Leyden jar after the city in which he taught. Soon after hearing about this effect, Daniel Gralath, a German physicist, found that he could attach multiple jars to increase a discharge which was strong enough to kill small animals and birds.

Curiosity was at an all-time high all over Europe. The well-to-do would gather to experience the effects of electricity. It was common for royalty to line people up hand in hand and watch them jump when discharging Leyden jars across them. Capacitors continued to be studied, and Benjamin Franklin eventually proved that the charge is not stored in the liquid, but on the glass.

Over the last 200 years, capacitors have been refined and come in many forms. A capacitor’s ability to store charge is measured in farads. A 1 farad capacitor will accept 1 amp and change 1 volt over 1 second. The surface area of the metal plates, distance between the metal plates, and the dielectric material are the major factors that determine the farad rating.

In this demonstration, I’ll charge a polarized electrolytic capacitor with a 9-volt battery. You will see the current flow momentarily on the meter, and then stop once the capacitor is fully charged. I’ll then remove the battery clips, and then discharge the capacitor with an LED. Some capacitors may hold a charge for hours or even days. Some of you may have experienced this when working on CRT-based TVs.

Here I’ll demonstrate the relationship of electrode distance and capacitance. The metal surface will be one electrode, and a disk with taped spaces on the edge, the other. The meter is set to nanofarads, and you’ll see the value go up when the electrode distance is very close. The maximum voltage a capacitor can tolerate is mostly determined by the dielectric breakdown voltage. For instance, placing material such as glass or plastic between electrodes will increase the maximum voltage but will reduce the farad rating.

The overlapping surface also plays a role in the farad rating. You can see the value goes down when I slide the upper electrode so there’s less overlap. This technique is commonly used in variable capacitors.

This is a fun demonstration of a switch capacitor circuit that illustrates how charges can be reconfigured to increase or decrease voltage. First I’ll charge up the capacitors in parallel, disconnect the power source, and then connect them up in series, which doubles the voltage across the capacitors. If we put the capacitors back in parallel, we can see their individual voltages have not changed besides the normal discharge rate of the capacitors.

You can also decrease the initial voltage by first charging the capacitors in series and then connecting them in parallel.

It should be noted that changing the configuration of the capacitors increases or decreases the available usable current. I’m demonstrating this by manually moving capacitors, but switching devices, like transistors or relays, would be more commonly used in power supplies.

The last example is DC blocking. Since the two electrodes don’t have direct electrical connection, electrons will not flow from one to the other. This prevents DC current from passing through a capacitor, but alternating current on one electrode will induce the current on the other electrode due to attraction and repulsion of charges. This is useful for changing the DC offset of a signal.

This video was sponsored by Adafruit Industries. You should go check out some of their electronic kits. They’re pretty fun to put together. They also have a live show that they do almost every Saturday. They show new products, and they show these videos. They also give away goodies a lot of times. And you can ask Lady Ada questions about engineering, and she’ll answer them live over U-stream. Thanks for watching

Batteries – A to Z of Electronics… The history and technology in batteries by Jeri Elsworth. This is part of our A – Z electronics series, we are sponsoring these videos for Jeri to create, we love these!

Most of us became familiar with what batteries do when we were just small children with all our battery-operated toys. But the history of its invention is packed with drama and uncertainty.

Artifacts were discovered outside of Baghdad that resemble batteries. They consisted of a terracotta pot with a copper cylinder and an iron rod held in place with an insulator. Some believe if they were filled with fruit juices, they would produce a small current. The most intriguing part of the story is that it pre-dates the official invention of the battery by at least 1500 years. Currently, there’s no definitive way to determine what these were really used for.

In the late 1700s, Luigi Galvani, a professor of anatomy, was performing experiments on frogs, trying to prove their testicles were in their legs. He made the observation that their legs would twitch when touched by a statically charged scalpel. He spent the next ten years performing experiments, and found that touching unlike metals simultaneously across the legs would cause them to twitch. He concluded that there were three types electricity: friction, lightning, and his newly discovered animal electricities.

But not everyone agreed with them. Alessandro Volta, a professor of physics, a self-proclaimed genius, and a ladies’ man was convinced there was only one type of electricity. I want the frog legs. He started his own experiments, and quickly discovered that frog tissue was not the source of electricity, but a sensitive detector. He found that he could use salt water-soaked felt in place with the frog tissue and still produce electricity.

He believe that he discovered an unlimited source of electricity that came from the tension of two dissimilar metals, and the corrosion of the salt water was only an annoyance. Because of this belief, his primitive batteries, or voltaic piles, have extra plates on the top and bottom.

We now know that the current is generated by a process of oxidation and reduction. Oxidation occurs at the more reactive electrode, and reduction happens at the less reactive electrode. The electrode that’s being oxidized will be consumed, and positive ions will diffuse away from it. Depending on the chemistry of the cell, at the reduction electrodes, sometimes gas is formed, and other times, it’s plated, and negative ions diffuse away. Externally in the circuit, the electrons flow from the oxidation electrode to the reduction electrode.

This is the electrical symbol for a battery. The small line is the negative terminal. See the resemblance?

This is a partial list of the activity series of metals, lithium being the most active, and gold being the least. The more active a metal, the more likely it will lose electrons and oxidize. To the right, you can see the standard oxidation potential in volts. In a perfect world, you can use these numbers to calculate out the voltage of your cell, depending on the electrodes you choose. If we chose zinc and copper, the difference would be about one volt.

You can create your own voltaic cell at home very easily with two dissimilar pieces of metal and a piece of paper soaked in vinegar. The bottom plate is a piece of copper. I’m not exactly sure what the washer is made of. When I test with the volt meter, I can see that it’s 0.8 volts.

We can tell that the washer is the anode, because the volt meter will indicate with a negative sign if the leads are hooked up backwards. Cells like this have a disadvantage, because they continue to react, even when current isn’t flowing.

An improved cell would have electrodes surrounded by a solution that only reacts when current is flowing. This can be achieved by using a salt bridge with a permeable membrane that allows ions to pass. Rechargeable batteries are very similar to one time use batteries. The difference is, the chemistry can be reversed, restoring the electolytes and the electrodes.

Lead acid is an example of this type of battery. During discharge, the electrodes are turned from lead and lead oxide to lead sulfate, and during charging, it’s returned back to lead and lead oxide and sulfuric acid.

You can increase the voltage of a battery by adding more cells stacked in series. I’ll demonstrate this by hooking 40 9-volt batteries together.

Oops. I’d better get some bigger electrodes.

If you need to increase current, you can put batteries in parallel. This is effectively making their plates a larger surface area.

Here I’m shorting a fine wire across the leads of the 9-volt battery. Not much happening. Now we see smoke when I hook two batteries in parallel, and short the lead. And with three batteries, it’s far too much current for such a small wire, and it immediately melts.

Well, I hope you liked the video about batteries. I had a great time putting it together, and I want to think my sponsors at Adafruit Industries. It’s their concept for this. Be sure to drop them a note and let them know that you like this, and better yet, buy something from them. You might check out their MintyBoost, which is a boost converter so you can charge USB devices from double A batteries.

You can always reach me at scorched.chips@gmail.com. I love hearing from you guys. Send me your suggestions.