Aluminium Capacitors Overview

Aluminium capacitors are very common electrical components that have been in use for over a century. They are electrolytic capacitors, which means that they have an electrolyte introduced into them, generally a paste in the case of these components.

An aluminium capacitor is a very simple device and the technology that makes it work dates back to the mid-1700s. A German scientist by the name of von Kleist is acknowledged as being the first to build a capacitor. The first common device that functioned as a capacitor, however, bears the name of a Dutch scientist, Leyden, who created the Leyden jar.

While the aluminium capacitor would come later, it shares much in common with the Leyden jar. The Leyden jar had metal on the inside and outside of the container. The glass provided the insulator against electricity flowing from one plate to the other, though the principle that creates capacitance was not fully understood at the time of invention.

The jar would be charged with a positive charge on the inside plate. The top was sealed with a stopper through which a metal chain descended. This was used to charge the device. Leyden discovered that he could discharge the capacitor he’d created by connecting the inside and outside plates. Until that connection was made, however, the device would hold the charge applied to it.

The jar was filled partially with water. At the time, this was thought to be integral to the device. Benjamin Franklin, however, later discovered that, by affixing two flat pieces of foil to a plate of glass, he could get the same result. The jar—and the water—were not necessary.

This work was still being done as experimental novelty. Eventually, Michael Faraday changed everything. An inventor and avid experimenter, he started using capacitors to hold unused charge from his experiments. His capacitors were made out of large barrels.

Faraday ended up being the scientist most associated with capacitors. His name was chosen for the measurement of capacitance, the farad. The farad is a very large number, so most capacitors are measured in decimal amounts of a farad.

While it took many years to develop the capacitor as a component, the basic workings of it are familiar to everyone. When you see lightening, you’re seeing the release of a stored charge. The clouds act as one plate in the capacitor and the ground acts as another. When it discharges, the electricity is observed in the arc of lightening that travels between the charged “plates”.

Those plates need not be so far apart as earth and sky. In fact, they function better when the separation between the plates is very small, which is achieved in aluminium capacitors by using the very thin sheet of paper to separate them.

 

The Advent of the Electrolytic Capacitor

The electrolytic capacitor—the type to which aluminium capacitors belong—has its roots in the first days of radio. As radio sets became more popular, the fact that they were mostly battery powered became very inconvenient for consumers. With mains power being available, it was natural to want to hook the radios up to this essentially endless source of electricity.

The problem with doing so stemmed from the noise that the AC power introduced into the circuit. You can still hear this on some devices, notably instrument amplifiers. It manifests as a humming noise.

A capacitor is the natural solution for this problem. A man named Lilienfield developed a capacitor that allowed people to plug their radios in and enjoy them without the distracting humming noise from the mains power. These capacitors were the basis of the aluminium capacitors in use today and heir design is very similar to the modern versions. They featured a dielectric placed between two conductors, which in today’s aluminium capacitors is the paper and two aluminium surfaces that make up the devices.

Capacitors are sometimes known by the name condensers, though the term capacitor is generally preferred in modern usage.

 

What Is an Aluminium Capacitor?

An aluminium capacitor is a type of electrolytic capacitor that is capable of achieving high levels of capacitance. This has kept the devices useful for many decades and, because they are inexpensive, they provide a low-cost solution to demanding and diverse engineering needs.

Aluminium capacitors come in a variety of sizes. They range from devices that can easily fit on a circuit board to devices that require a great deal of space. Some of the largest with which most people are likely familiar are the beverage can sized capacitors that are found in the back of older television sets.

 

Which Parts Reside Within an Aluminium Capacitor?

The internal components of an aluminium capacitor are quite simple. They consist of an aluminium oxide layer, aluminium foil and capacitor paper, which is also known as electrolytic paper.

The electrolytic component contributes to the formation of a lawyer of oxide that is vital to the function of these devices. When that oxide layer provides the forward direction insulation of the capacitor.

Pulling such a capacitor apart, one would see two strips of aluminium foil with the paper between them. The two strips of aluminium function as the anode and the cathode of the capacitor, with the paper providing a barrier between them. The foil is wrapped around a structure and the wrapped parts are treated with the electrolyte.

The dielectric in an aluminium capacitor is aluminium oxide. Other capacitors employ different dielectrics to archives their capacitance, but the aluminium oxide is always the dielectric in an aluminium capacitor.

There are two variations on these capacitors. Some of them have plain foil and some of them have foil that has been etched with a chemical. The etched foil types have a larger surface area. The etched types can provide higher capacitance in a smaller package than the plain types, but they are not as tolerant of high DC currents. They are also characterized by having a higher tolerance value than the plain foil types.

These devices are very easy to disassemble, provided one makes certain that they are fully discharged beforehand. This can be done by connecting the device to a load—such as a lamp—that will give an indication when the capacitor is completely discharged. After it is, the outer casing can be cut away, revealing an inner sleeve into which the device is packaged. Removing that sleeve will reveal the rolls of aluminium foil and the paper that separates them, which are very tightly packaged into the device.

Because they do contain materials that may be harmful, it’s important to make sure you’re prepared with protection from anything inside the component.

 

What Happens Inside an Aluminium Capacitor?

The basic function of a capacitor is to take an electrical charge and hold it. They’re not batteries, but they do provide a way to store electrical charge for other purposes.

In the capacitor, a charge is delivered from the positive side of the circuit through the anode. This is prevented from travelling through the capacitor by the dielectric layer. In this case, that’s the aluminium oxide. When the capacitor is discharged, the charge is released very quickly. This is why large capacitors have to be discharged before handling them and why older television sets, which had very large capacitors in them, are dangerous to those who don’t know how to properly handle capacitors.

Aluminium capacitors, at the most basic level, function as does any other capacitor. The dielectric provides an insulating layer that prevents current from flowing from the anode side to the cathode side of the device. Ideally, they would be able to do this without any leakage, but leakage is a factor in any practical capacitor.

Should an aluminium capacitor overload and present a danger of explosion, there is usually a valve on the device that is designed to diminish the pressure, preventing such a catastrophe. This does drive home the point, however, that the workings of a capacitor can present some hazards. It’s imperative that these devices are hooked up according to the proper polarity, as reversing the leads can end up causing the capacitor to fail in dangerous ways.

 

Which Companies Produce Aluminium Capacitors?

These components are so common that they are produced by a huge range of different companies. Some of the most well-known names include.

 

  • ebm-papst
  • Epcos
  • Illinois Capacitor
  • Nippon Chemi-Con
  • Nichicon
  • Cornell-Dubilier
  • Kemet
  • Visay
  • Yageo
  • Sanyo
  • Robycon
  • RS
  • Phycomp
  • Panasonic

 

There are many others that produce these devices.

 

What Is Considered the Capacitance of an Aluminium Capacitor?

The capacitance of an aluminium capacitor is its most important quality. It describes how much electric charge the device can store.

Capacitance is measured in farads, abbreviated “F”. This is a very large unit, so much capacitors are measured in decimals of farads, including mili and micro farads. Even smaller capacitance values are available, including nano, pico and femto farads.

Capacitance can be calculated by determining the charges on the plates and the voltage between them using the formula C=q/V.

 

What Is the Tolerance of an Aluminium Capacitor?

No capacitor is ideal, so there is always some degree of tolerance that has to be considered when using them in builds. The tolerance is expressed in a percentage and describes the percentage of the rated value by which the capacitor might vary in use. This may change if the capacitor becomes hotter or colder during use. The basic measurement is calculated at a temperature of 20 degrees centigrade.

 

What Is the Equivalent Series Resistance?

A capacitor, ideally, would only lend capacitance to a circuit. Given that no electrical components are ideal, however, capacitors introduce resistance into a circuit, as well. This is measured as the equivalent series resistant. In electrolytic capacitors that have a liquid or past electrolyte, this value can be into the range of several ohms. This value also increases over time and can increase if the frequency of the signal passing through the capacitor increases, as well.

 

What Is the Definition of Ripple Current in an Aluminium Capacitor?

In circuits where AC is being converted to DC, the ripple current is a small variation in the DC that remains from the AC.

 

What Is the Lifetime of an Aluminium Capacitor?

An aluminium capacitor’s lifetime is measured in hours and describes the amount of time that the device can be expected to reliably function. A year is roughly 9,000 hours long, so a capacitor with a lifetime of 9,000 hours could function reliability if left on for a period of around 1 year before it started to lose reliability.

 

What Are the Different Types of Construction of Aluminium Capacitors?

Aluminium capacitors can be constructed in several different ways. They include axial designs, cylindrical designs and flat designs. The most well-known are likely the can designs, which look much like their namesakes. These are usually larger devices that are commonly hooked into the circuit board but located off of it, owing to the amount of space that they take up.

 

What Is Considered the Leakage Current of Aluminium Capacitors?

Leakage current is unwanted current that leaks out of the capacitor. This can occur when the capacitor is powered off and it leaks a small amount of current into the circuit. It can also occur when some charge manages to penetrate the dielectric, which can permit some of the energy stored in the capacitor to leak out doing usage.

 

What Does the Maximum Operating Temperature and the Minimum Operating Temperature of an Aluminium Capacitor Mean?

Aluminium capacitors are affected by temperature. These figures indicate the maximum and minimum temperatures that a capacitor can function at and be expected to remain within tolerances. Exceeding these values at the upper end with capacitors that have a liquid electrolyte can result in explosions.

 

What Is Meant by Tolerance Minus and Tolerance Plus of an Aluminium Capacitor?

The tolerance plus rating is the highest that a capacitor can go above its specified rating without exceeding the specifications of the component. The tolerance minus is just the opposite.

 

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