November 22, 2022

Electrolytic Capacitor: Function, Lifespan and Failure Modes

An electrolytic capacitor has one of the biggest capacitances compared to other capacitors. It is used in electrical circuits with a low frequency and high current, such as the circuits of a power-supply filter which have fluctuating currents and output voltage. If there are no rechargeable batteries present, then an electrolytic capacitor can offer the same kind of low-frequency electric current capacity.

Basic Function and Working Principle

There are polarized components within electrolytic capacitors because they’re constructed asymmetrically. The reason for this construction is due to their higher voltage operation where one side receives more power than the other side. They have a metal or aluminum anode with an oxidized cover layer, which is the dielectric, and serves as the positive electrode of the capacitor. This is the side which receives most of the input voltage.

The cathode serves as the negative electrode and contains aluminum foil and a liquid electrolyte. This liquid usually consists of a combination of water and sodium borate or boric acid. There are also a few sugars added to prevent evaporation. Make sure you don’t get this liquid in your eyes, mouth, or skin because it is very dangerous to your health. Immediately wash off the liquid if it encounters any part of your body.

The aluminum oxide is what enables the polarity of the electrolytic capacitors. The electric field holds the aluminum oxide in place. When direct current (DC) voltage is being supplied to the electrolytic capacitor, the proper polarity needs to be there. This requires the positive lead and positive terminal to be connected and the negative lead and negative terminal to be connected. If this is not done properly, it will ruin the capacitor.

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Lifespan

Electrolytic capacitors are required for all power supplies which use alternating currents and direct currents. As the power demands for electronic components increase each year, it also changes the way in which electrolytic capacitors are designed. The design ultimately determines the lifespan of the capacitor. Some internal components cannot handle the excessive heat that is generated from the input voltage demands. That is why you need to shop around and pick the best capacitor possible that has the longest lifespan.

The minimum lifetime of an electrolytic capacitor is between 1,000 and 2,000 hours, while the better-quality designs have 10,000+ hours of life. You’ll obviously want an electrolytic capacitor with a long lifespan because it means the application will last a long time as well. Capacitor manufacturers calculate the lifespan by considering the maximum rated ambient temperature.

In most cases, the maximum temperature is 105°C. So, if you have an electrolytic capacitor with a 5,000-hour lifetime, then it is possible to increase the lifetime if you can reduce the temperature. Every 10°C drop in temperature will double the lifetime of the capacitor. That means if the temperature is 95°C, then the total lifetime is 10,000 hours. If the temperature is 85°C, then the lifetime is 20,000 hours.

Failure Modes

Electrolytic capacitors are not perfect. It is possible for them to fail at doing their job, which could lead to leakage and bulkage. Fortunately, you can investigate the failure modes to figure out the reason why the capacitor failed. Since most electronic devices have a Low Equivalent Series Resistance (ESR) when using an electrolytic capacitor, then a High ESR is one failure mode. You can use an ESR meter to test and see whether this is the case.

If the proper amount of ESR is measured on the metering tool, then you might have a low capacitance failure mode. To verify this, you’ll need to use a capacitance meter to find out what the capacitance level is at. However, sometimes the failure might be related to the capacitor not opening, which means that the electric flow cannot be distributed properly to the circuits. Only an experienced technician can diagnose this problem.

If none of these failure modes exists, then you have a short in the capacitor. This is the worst of them all because it means your capacitor is damaged and will need to be replaced.

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