Power storage has always been a defining component of electrical products, “defining” meaning the make-or-break for whether the technology is feasible. For many amazing feats of technology found in our favorite science fiction movies and comics, it’s not a question of “How do we make them work?”, it’s “How do we power them?”.
Two current examples making headlines in the past few years are home power banks and electric cars commonly referred to as “EV”s. It wasn’t until the past 10 years that battery technology advanced enough to make these possible. These advancements include capacity, reliability, cost, and a reduction in environmental impact. The Tesla Powerwall was only introduced in 2015 thanks to these advancements. Through testing in Powerwall systems, further advancements were able to be made for EV batteries. But, even with these strides, many EV manufacturers still use another energy storage technology known as supercapacitors for their regenerative braking systems.
In this article, you will learn what a capacitor, supercapacitor, and battery are. We will cover the key similarities and differences in function and application.
Similarities
Capacitors, supercapacitors, and batteries all serve a similar general purpose, to store electrical power for later use. What differs is how this is accomplished, how much energy can be stored, and how quickly it can be charged and discharged. All of these components require a connection to positive and negative leads in a circuit to “collect” a charge. We will use “collect” as a generic term because the actual processes are much more specific and this isn’t a full-length physics course. Once connected to positive and negative leads in a circuit, one of two processes will take place depending on the type of capacitor or battery. Either a building of a static charge or a chemical conversion will take place to create a difference of potential.
Capacitors
There are several types of capacitors used for different purposes. Some are intended to store incredibly high voltages, but very little charge, analogous to a pressure washer hose versus a large drain pipe. Instead of listing all of the types of capacitors, a subject to which there are entire textbooks and graduate-level courses devoted, here are the basics you need to know.
The most basic capacitor structure is two metal plates with a dielectric insulator sandwiched between them. When a charge is applied to the two plates, electrons are pulled from the molecules from one plate to the other. The molecules don’t like this because they always want to remain neutral. By moving some of their electrons from one plate to the other, it creates a difference of potential giving one plate a negative charge and leaving the other with a positive charge. When the circuit is disconnected from the capacitor, this difference in charge remains because of the insulating material in between. While in reality, the insulator is never perfect allowing for “leaks” resulting in a gradual discharge as well as environmental leaks.
There are two major groups that capacitor types are categorized into: polarized and non-polarized. The term “polarized” means that the charge can only be applied in one direction, there is a positive side and there is a negative side. Reversing the connections on these types of capacitors will, at best, render them useless if not destroy them. In contrast, the non-polarized varieties don’t care which lead is connected to what. Non-polarized varieties tend to have much lower capacitance values than that of polarized meaning they are used for very small charges.
Ceramic and film capacitors are the most popular non-polarized, featuring several varieties within themselves for specific applications. They are highly economical and very simple in their construction, most resembling closely to the previously mentioned plates and dielectric sheet example. The amount of charge they can hold is determined by how well the metal sheets are insulated from one another and how many sheets are layered. Most ceramic capacitors are a simple setup of just one pair of plates meaning they can withstand incredibly high voltages but have limited capacitance typically falling between a few pico-farads up to 0.1 micro-farads.
Electrolytic capacitors operate on the same principles but have a key difference. Instead of stacked sheets or films of material, the two metal strips are rolled into a