Why Electrolytic Capacitors Fail (And How to Prevent It)

Electrolytic capacitors are everywhere. Power supplies, motor drives, industrial controls, medical devices, EV systems, consumer electronics. If a product converts, stores, filters, or smooths power, there is a strong chance an electrolytic capacitor is involved.

They are also one of the most common points of failure in electronic assemblies.

For new manufacturing and design engineers, understanding why electrolytic capacitors fail and how to prevent them is essential for improving reliability, reducing RMAs, and avoiding costly field failures.

1. What Makes Electrolytic Capacitors Different

Electrolytic capacitors achieve high capacitance values in a small footprint by using a liquid or gel electrolyte and a very thin oxide dielectric layer.

That construction gives them advantages:

• • High capacitance per volume
  • Cost effectiveness
  • Good performance in power filtering applications

It also gives them inherent weaknesses:

• • The electrolyte can dry out or degrade
  • The dielectric layer is chemically fragile
  • Performance is highly sensitive to temperature, voltage, and ripple current

In short, electrolytics are not “install and forget” components. They age.

2. The Most Common Reasons Electrolytic Capacitors Fail

2.1 Electrolyte Dry-Out (The #1 Failure Mode)

Over time, the electrolyte slowly evaporates or chemically degrades.

This causes:

• • • • Increased ESR (Equivalent Series Resistance)
      • Reduced capacitance
      • Excessive heat generation
      • Eventual open-circuit or catastrophic failure

High temperature accelerates this dramatically.
A common rule of thumb: every 10°C increase cuts capacitor life roughly in half.

2.2 Excessive Ripple Current

Ripple current flows through the capacitor during normal operation, especially in:

• • • • Switching power supplies
      • DC-DC converters
      • Motor drives

If ripple current exceeds the capacitor’s rating:

• • • • Internal heating increases
      • Electrolyte degrades faster
      • ESR rises, creating a destructive feedback loop

This is one of the most frequent design-stage mistakes.

2.3 Overvoltage Stress

Applying voltage too close to or beyond the rated value damages the oxide dielectric.

Consequences include:

• • • • Increased leakage current
      • Internal heating
      • Gas generation and bulging
      • Vent rupture or explosion in extreme cases

Transient spikes and poor derating practices are common culprits.

2.4 Temperature Exposure (Ambient and Self-Heating)

Electrolytic capacitors suffer from both:

• • • • Ambient heat from the environment
      • Self-heating from ripple current and ESR

Mounting a capacitor near:

• • • • Heat sinks
      • Power MOSFETs
      • Transformers

…can significantly reduce its lifespan, even if the datasheet ratings appear acceptable.

2.5 Reverse Polarity or Incorrect Installation

Most electrolytic capacitors are polarized.

Reverse installation can cause:

• • • • Rapid dielectric breakdown
      • Gas generation
      • Venting or violent failure

This failure often appears during:

• • • • Prototyping
      • Rework
      • Manual assembly operations

2.6 Mechanical and Manufacturing Stress

Manufacturing-related issues are often overlooked:

• • • • Excessive soldering temperature or time
      • PCB flexing
      • Vibration in industrial environments
      • Poor lead support on large radial capacitors

These stresses can crack internal connections or compromise seals, accelerating electrolyte loss.

3. How Electrolytic Capacitor Failures Appear in the Field

Manufacturing and quality teams often encounter:

• • Bulging or domed capacitor tops
  • Leaking electrolyte residue
  • Burn marks near capacitor bases
  • Boards that pass test but fail after burn-in
  • Intermittent or temperature-dependent failures

In many cases, the capacitor still “measures okay” at room temperature, masking the root cause.

4. How to Prevent Electrolytic Capacitor Failures

4.1 Apply Proper Voltage Derating

A common best practice:

• • Use 50–70% of the rated voltage for long life designs

Example:
Use a 50V capacitor on a 24V rail, not a 25V part.

This reduces dielectric stress and leakage current.

4.2 Design for Ripple Current Margin

Never design to the limit.

Recommendations:

• • • • Calculate worst-case ripple current
      • Include temperature effects
      • Choose a capacitor with 20–50% ripple current margin

When in doubt, use multiple capacitors in parallel to share ripple current.

4.3 Control Temperature Aggressively

• • • Select capacitors rated for 105°C or 125°C, not 85°C
    • Increase spacing from heat-generating components
    • Improve airflow where possible

Thermal layout decisions matter just as much as electrical ones.

4.4 Choose the Right Capacitor Type

Not all electrolytics are the same:

• • • • Aluminum electrolytics for bulk capacitance
      • Polymer electrolytics for low ESR and longer life
      • Hybrid types for improved stability

In some designs, replacing electrolytics with:

• • • • Ceramic
      • Film
      • Polymer

…can eliminate failure mechanisms entirely.

4.5 Respect Manufacturing Best Practices

For manufacturing engineers:

• • • • Control solder profiles carefully
      • Avoid prolonged hand-soldering
      • Use strain relief for large capacitors
      • Train operators on polarity awareness
      • Inspect for mechanical stress and board flex

Small process changes can prevent large reliability problems.

5. Designing for Reality, Not Just the Datasheet

Datasheets are written under controlled conditions.
Real products live in:

• • • Hot enclosures
    • Noisy power environments
    • Vibrating machinery
    • Long service lifetimes

Electrolytic capacitors are often the clock that determines system life.

Design engineers who treat them as consumable components and plan accordingly produce more reliable products.

6. Key Takeaways for New Engineers

• • Electrolytic capacitors fail primarily due to heat, ripple current, and time.
  • Failure is predictable and preventable.
  • Proper derating and layout decisions matter.
  • Manufacturing practices can extend or destroy capacitor life.
  • When reliability matters, capacitor selection is a system-level decision.

Final Thought

If a system fails in the field after three to five years, the electrolytic capacitor is often the first suspect.

Understanding why they fail and how to prevent it turns a common weakness into a controlled design variable.