Introduction to Aluminum Capacitors: Traditional Electrolytic vs. Polymer

In the wide world of capacitors, it can be difficult to know which capacitor to choose for your application (and why).

There are three main types of capacitors: ceramic, film, and aluminum electrolytic. In this blog series, we will focus on the latter, specifically looking at the difference between the two main types of aluminum capacitors: traditional electrolytic and solid polymer.

Read on to learn the most important factors in comparing aluminum electrolytic capacitors.

Technical Basics of Capacitors

Before we begin an advanced discussion of aluminum electrolytic capacitors, it may help to review the technical basics of capacitors in general.

There are three main parts of a capacitor:

  • Electrodes
  • Dielectric material
  • Distance between electrodes

These are the three key parameters you can use to distinguish the power and manipulate the capacitance of a capacitor. So how do you do that?

To increase the performance of a capacitor, you can change one of the following three parameters:

  • Surface area: The surface area of the two conductive plates that make up the capacitor (the larger the area, the greater the capacitance)
  • Dielectric material: The type of material that separates the two plates, called the “dielectric” (the higher the permittivity of the dielectric, the greater the capacitance)
  • Distance: The distance between the two plates (the smaller the distance, the greater the capacitance)

But those parameters are just the beginning of the factors used to determine a capacitor’s performance. There are several other considerations to take into account.

Equivalent Series Resistance (ESR)

The first factor to consider when attempting to increase the performance of a capacitor is the equivalent circuit inside the capacitor.

There are several components inside the capacitor that determine the equivalent circuit, including:

  • Equivalent Series Inductance (ESL)
  • Equivalent series resistance (ESR)
  • Isolation resistance (RISO)
  • Leakage current (RLEAK)
  • Capacitance (C)

Of these, the ESR value may be the most important. Obtaining a low ESR value is critical to increasing a capacitor’s performance.

Basically, ESR causes heat generation within the capacitor when an AC ripple current flows through the capacitor. The maximum ESR is normally specified at 120Hz or 100kHz at 20°C, though you typically want it to be much lower than that.

Here’s where we begin our comparison between the two main types of aluminum capacitors: electrolytic and polymer. While ceramic capacitors have lower ESR values than both of them, aluminum polymer capacitors have a much lower ESR than traditional electrolytic capacitors — giving them a major advantage over the traditional sort.

Electrolytic Conductivity

The next factor to consider when comparing the performance of the two types of capacitors is their electrolytic conductivity.

The aluminum electrolytic is rated up to 0.04 S/cm, while the aluminum polymer is rated up to 4 S/cm — a whole 100 times higher! This is because the aluminum polymer uses a solid rather than a liquid electrolyte, thus lowering the ESR value and pushing the conductance response to much higher limits.

Here is a breakdown of the electrical values, so you can see the conductivity advantages of the aluminum polymer for yourself.

Ripple Current > Temperature Rise

The ripple current is another important element of capacitor performance.

The ripple current is the AC component of an applied source, such as a switched mode power supply (SMPS). Ripple current is caused by the changing field strength and current flow through the capacitor.

Ripple current causes heat inside the capacitor due to the dielectric losses. Heat is the main influence in lowering the lifetime of a capacitor.

Because the conductivity of the polymer is 100 times that of the electrolytic in fact, the ESR is way lower, it generates much less heat — and therefore has a much longer life time.

Impedance at High Frequencies

Another significant factor in determining a capacitor’s performance is its impedance value, especially at high frequencies.

When you raise the frequency to a certain MHz level, the capacitor is not really a capacitor anymore; it becomes more of an inductor. So when working with impedance values, it’s important to ask yourself: What kind of frequency will pass over the capacitor so that it is still close to the resonance point (and so that it maintains its true capacitance character)?

At high frequencies, aluminum polymer capacitors have excellent high-frequency characteristics. As we mentioned, that means their ESR value is much lower (and their performance is much better) than both electrolytic and tantalum capacitors.

Some examples for applications where aluminum polymer capacitors offer better performance include couple capacitors, pulse applications, and ESD and audio equipment.

Temperature Characteristics in Comparison

Another important factor when comparing aluminum polymer with aluminum electrolytic capacitors is the temperature range they offer. Depending on your application, you may need a capacitor with a high or low temperature range.

If you’re looking for a low temperature range, the aluminum polymer offers excellent stability thanks to its solid nature. On the other hand, the low ion mobility inside the liquid electrolytic causes its performance to drop during low temperatures, resulting in both capacitance decline and ESR increase.

Learn More about Aluminum Electrolytic Capacitors

Eager to learn more about aluminum electrolytic capacitors vs. polymer electrolytic capacitors?

Stay tuned to our blog for an in-depth analysis of both types of capacitors, or check out our ABC of Capacitors design guide!

Ready to see the capacitors in action? View our product pages for aluminum electrolytic capacitors and aluminum polymer capacitors online!

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