What Is an Electrolytic Capacitor?
An electrolytic capacitor is a polarized capacitor that offers high capacitance in a small size. It's usually used for energy storage and filtering in power supplies.
Structure and Operation
Inside it there's a liquid/gel electrolyte and a thin oxide layer; this structure allows very large capacitance values (µF–mF). But by its nature it's directional.
Polarity (Critical!)
It has plus (+) and minus (−) terminals; the stripe on the body usually marks the negative terminal. If installed backwards it can overheat and explode — this is the most common and most dangerous mistake.
Properties
| Property | State |
|---|---|
| Capacitance | Very high (µF–mF) |
| ESR | Relatively high |
| Lifetime | Limited (electrolyte dries out) |
| Temperature | Seriously affects lifetime |
Where Is It Used?
Common in smoothing ripple at a power-supply output, energy storage and low-frequency filtering.
Lifetime and Temperature Relationship
An electrolytic capacitor's lifetime is limited because the liquid electrolyte inside dries out over time. Temperature speeds this up: every ~10 °C rise in operating temperature roughly halves the lifetime. So keeping them away from heat sources (regulators, power transistors) and choosing a suitable temperature class (e.g. 105 °C) markedly extends the lifetime.
Common Mistakes
- Reverse polarity: risk of explosion/leakage; the direction must always be checked.
- Using it at high temperature: every 10 °C rise roughly halves the lifetime.
- Pushing the voltage limit: running near the rated voltage shortens the lifetime.
Frequently Asked Questions
Why does a capacitor swell?+
Which terminal is negative?+
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