What Happens If a Capacitor Is Not Used for a Long Time?

Capacitors are vital components in almost every electronic device, but many users wonder: Do capacitors go bad if not used? Whether you’re dealing with old stock, spare parts, or unused components in long-term storage, understanding how capacitors age and how to keep them reliable is essential for both professionals and DIYers.

Understanding Capacitors: What They Are and How They Work

What Is a Capacitor?

A capacitor is a passive electronic component that stores and releases electrical energy in a circuit. It consists of two conductive plates separated by a dielectric (insulating) material. When voltage is applied, the capacitor stores energy, which can be discharged later as needed.

What Is a Capacitor Used For?

Capacitors help regulate voltage, smooth out power supply fluctuations, filter noise, and enable timing and signal processing functions. They’re found in devices ranging from power supplies and motors to audio equipment and industrial machinery.

Capacitors are used in a wide range of applications, including:

Power electronics – smoothing voltage and filtering signals
Motors – starting or running capacitors
Lighting – improving power factor in fluorescent or HID lighting
Timing circuits – paired with resistors to control timing
Energy storage – as part of backup systems or energy harvesting designs

Knowing what a capacitor is used for can help you determine how critical its performance is in your system, especially after long-term storage.

Do Capacitors Go Bad If Not Used?

Yes, capacitors can degrade over time even when not in use. While they may appear intact physically, internal deterioration can affect their performance or lead to failure when reactivated. Here are some possible scenarios:

Capacity Loss: Capacitors may lose some of their capacity when left unused for an extended period of time. This is because the capacitor's dielectric (usually a dielectric material) may gradually break down or degrade, causing the capacitor to be unable to store the same amount of charge. This phenomenon is more common in ceramic capacitors and electrolytic capacitors.
Increased leakage current: Capacitors that have not been used for a long time may cause increased leakage current. This is because the insulating material in the capacitor may no longer effectively isolate the charge due to age, allowing current to escape.
Capacitor damage: If the capacitor is stored under extreme conditions, such as high temperature or high humidity environments, or is subjected to excessive voltage, it may cause damage to the capacitor if it is not used for a long time. This may include deterioration of insulation materials or corrosion of electrodes.

These effects are more pronounced in electrolytic capacitors, while film capacitors and ceramic capacitors generally offer better shelf-life stability. Overall, long periods of disuse of a capacitor will not necessarily lead to immediate failure, but may have a negative impact on its performance and lifespan. If you need to use capacitors that have not been used for a long time, it is recommended to check them before use to make sure they are still functioning properly, or consider using them regularly to maintain their performance.

Why Do Capacitors Go Bad If Not Used?

Capacitors age naturally over time due to environmental factors and internal chemical changes. When not powered on regularly, electrolytic capacitors may lose their oxide dielectric layer, increasing the risk of failure when re-energized.

Key causes include:

Temperature fluctuations causing material stress
Humidity and moisture penetrating seals and causing corrosion
Electrolyte evaporation or leakage
Chemical degradation of internal materials

Electrolytic capacitors especially need “reforming”, which involves applying a voltage gradually to restore their dielectric layer if they haven’t been used for several years.

How to Store Capacitors for Long-Term Use

To extend the lifespan of unused capacitors and prevent failure:

✅ Store in a dry, controlled environment

✅ Maintain temperature between 5°C and 35°C

✅ Avoid exposure to humidity, dust, or corrosive gases

✅ Keep them in sealed, anti-static packaging

✅ For electrolytic capacitors: apply rated voltage every 1–2 years to reform the dielectric

Proper storage helps reduce the chances that your capacitor will go bad during inactivity.

How to Check if a Capacitor Is Still Good

Before using a capacitor that has been in storage:

Measure capacitance with an LCR meter
Check leakage current
Inspect for bulging, corrosion, or leakage
Test ESR (equivalent series resistance)

If the readings are significantly off, the capacitor may no longer be reliable.

Pay Attention to Unused Capacitors

If you're dealing with capacitors that haven't been used for a long time, don't assume they're still in perfect working condition. While some types, like film capacitors, can last for years on the shelf, others—particularly electrolytic capacitors—may degrade or fail.
By understanding how and why capacitors go bad when not used, and by storing them properly, you can reduce the risk of failure and ensure long-term performance for your equipment.

As a leading capacitor supplier, Lung Chen offers reliable metallized film capacitors, fan capacitors, motor capacitors, and custom capacitor solutions designed for durability and performance. Contact us for more about capacitor products.