Why Use Aluminum Polymer Capacitors?

Our last two blog posts have covered the technical basics of the two main types of aluminum capacitors ( traditional electrolytic and solid polymer) as well as the pros and cons of the traditional sort.

In this post, we will look specifically at the polymer type and how it compares to the traditional construction. We will conclude our blog series on capacitors with an overview of the enemies and applications of aluminum electrolytic capacitors in general.

Construction of Solid Polymer Capacitors

At first, the construction of polymer capacitors seems similar to that of aluminum electrolytic capacitors — you have the anode foil, the cathode foil, and different paper separators in between.

But the similarities stop there. Instead of a liquid electrolyte, the polymer capacitor has a certain monomer that will be filled into the separator element. Afterward, the so-called aging process (or drying process) will begin. After a period of two and eight hours, the polymerization process will start, and eventually the liquid monolayer will be transformed into a solid polymer.

Here are some of the current developments in the realm of polymer electrolytic capacitors:

  • 5.000h —> 10.000h —> 20.000h
  • 125 and 150°C
  • 100V - 125V
  • ESR << 3,5mOhm

Comparison of Polymer vs. Traditional Aluminum Electrolytic Capacitors

Now for the million-dollar question: Are polymer electrolytic capacitors or traditional electrolytic capacitors the better option for engineers? The answer depends on your design needs, as there are unique advantages to each.

Pros of aluminum electrolytic capacitors:

  • Higher voltage ratings available (up to 600V)
  • Way cheaper pricing (for the same capacitance and voltage)
  • Better leakage current behavior than polymer

Pros of polymer electrolytic capacitors:

  • Lower ESR/higher allowable ripple current
  • No dry-out behavior (unlike aluminum capacitors)
  • Higher expected lifetime/load life

It’s important to note that, when calculating the expected load life of a capacitor, you must take into account the temperature in which your application will work. At 105°C, for instance, the aluminum electrolytic capacitor has a longer life, but as the temperature drops to a more normal range of 65°C, the polymer electrolytic capacitor has a longer life. There are two different formulas to accurately calculate the life time. Please check out our ABC of Capacitors guide for more details.

In the end, it’s up to you to decide which type of aluminum capacitor will work better for your design. If you need a cheaper option with higher voltage ratings, stick with the traditional sort; however, if you’re willing to pay a little extra for better performance, try the polymer sort.

Enemies of Capacitors

Whichever type of aluminum capacitor you go with, note that both types have at least three enemies that will decrease their lifetime:

  • Humidity (moisture): Creeping of humidity in a layered dielectric can decrease the εr and thus the capacitance; can also result in insulation issues and destruction of electrodes
  • Temperature: Heat can increase the aging effects dramatically; can also change capacitance over temperature range
  • Time: Aging behavior can cause dry-out and other issues over time

Applications of Capacitors

Finally, let’s end our discussion with a brief introduction to the various applications of capacitors.

Among the three main types of capacitors — ceramic, film, and aluminum electrolytic — there are several applications that would work with two or all types. Applications that overlap all three areas include:

  • Coupling or blocking
  • Smoothing
  • Decoupling or bypassing
  • Noise filtering

Some applications only work with aluminum electrolytic capacitors. These include:

  • DC/DC, DC/AC, and AC/AC converters (>500W)
  • Frequency converters
  • Spot welding
  • Flashtube ignition
  • DC link
  • Motor start
  • Audio crossover
  • UPS buffering
  • DC buffering

And then there are a few applications that could work with either aluminum electrolytic capacitors and ceramic capacitors or aluminum electrolytic capacitors and film capacitors:

  • Power line buffering
  • Voltage doubling
  • Lighting ballast
  • Power factor correction (PFC)
  • Motor control

If you are searching for a high-capacitance solution for one of these applications, consider using aluminum electrolytic capacitors. While you may be tempted to use ceramic or film capacitors, alternatives like polymers may very well give you a much better performance.

Learn More about Aluminum Electrolytic Capacitors

Eager to learn more about aluminum electrolytic capacitors vs. polymer electrolytic capacitors? Read our latest blog posts, 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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