Effect of Storage Conditions on Electrolytic Capacitors

Aluminium electrolytic capacitors usually have body of aluminum, which is prone to degradation by exposure to corrosive weather and humidity. Usually manufacturers advise storage of idle capacitors at temperatures between 5 to 35℃, and humidity of under 65%. Container material gets affected by salts in atmosphere, and particularly in salty weather. Effect of atmosphere causes holes in body, through which all electrolyte leaks out, damaging the capacitor permanently. Collection of dust and dirt in humid atmosphere also hastens the degradation of container. Atmosphere with ammonia or other chemical contents must also be avoided for same reason. Conditions of prolonged direct sunlight, ozone UV radiations are not good for long time. Extreme and shocks are not good for these capacitors.

Therefore, aluminium electrolytic capacitors should be stored under specific conditions to ensure their optimal performance and long life. If aluminium electrolytic capacitors are stored over a long period of a year or more, oxide layer on anode slowly dissolves in electrolyte, affecting its voltage withstand strength.  It may be re-conditioned / reformed by applying a low voltage, and then applying full voltage for a short time before use. Even then, it is likely that over 2-3 years idle period, oxide layer of these capacitors may degrade to a state as to be unusable.

Most common reason for reduced life of electrolytic capacitors is evaporation or leakage of electrolyte. Temperature aggravates the ageing of electrolytic capacitors.  Life mentioned by manufacturer is under specified nominal voltage, current and temperature, in terms of nominal voltage, current temperature limits, loss angle / leakage current.  If all conditions are observed, capacitor life is many times the life of equipment.

Temperature affects life of capacitor adversely due to increased chemical reaction rate. Temperature rise leads to capacitance drop, increase in loss factor, self-heating and gradual evaporation of electrolyte through leaked seals. Self-heating can be major consideration in high power applications.

Most common causes of electrolytic capacitor failures are:

• Temperature
• Humidity
• Vibrations
• Atmospheric pressure

These conditions are usually specified by manufacturers in their datasheets / recommendations. Other factors which affect the life include applied voltage, charge / discharge duty cycles, ripple currents, and harmonics.

Recommended storage conditions for aluminium electrolytic capacitors are as under:

1- Temperature: Cool and dry environment within temperature between 5℃ to 35℃.xposure to extreme temperatures can affect their performance adversely. Drying of capacitor contents can result, leading to a loss of capacitance value over time and increase in ESR. These factors affect performance and reliability of capacitor. Lifespan of capacitor is reduced.

2- Humidity below 70% is recommended. High humidity can lead to moisture absorption, as also degradation of can, both of which are harmful to capacitor. It also increases leakage current if humidity is high, in which case capacitor loses capacity to hold charge for long time.

Capacitors may not fully recover their performance after exposure to high heat and humidity. Extent of recovery depends on the severity of temperature and humidity levels, as also characteristics of capacitors. Particularly loss of value and ESR cannot be recovered. Thus it is important to avoid excessive temperatures and humidity levels.

3- Exposure to direct sunlight is to be avoided. Prolonged exposure to sunlight can lead to heating and deterioration of capacitor.

4- Protect the capacitor from dust and dirt. It is better to store capacitors in sealed containers / boxes away from direct sunlight.

5- Avoid any mechanical stresses on containers by way of stacking pressure or otherwise. This can prevent physical damage to capacitors.

For tantalum and Niobium capacitors

It is recommended to store tantalum and Niobium capacitors in original packing, or in anti-static bags to protect them from dust, dirt and moisture, and to avoid physical damage.

1- Storage under temperatures between 20℃ and 25℃ is the most recommended.

2- relative humidity below 60% is recommended, as moisture absorption leads to increases leakage current and degradation of capacitors.

3- While handling of Tantalum capacitors, it is advisable to follow Electrostatic Discharge (ESD) procedure to prevent damage.

4- Avoid excessive force or mechanical stress, as rough handling can cause damage to capacitor and affect its performance.

5- Tantalum capacitors have limited shelf life of 2 to 5 years, depending on manufacturer and type. It is better to check manufacturer datasheet and ensure their usage within recommended timeline. It is further recommended to store Tantalum capacitors in moisture-proof boxes / bags.