What Is ESR in a Capacitor? Typical ESR Values Table
ESR (Equivalent Series Resistance) is one of the most important reasons capacitors fail in power supplies. Use this guide to understand ESR meaning, typical ranges, and what readings indicate replacement is needed.
Important: ESR Is Context-Dependent
The same ESR value can be acceptable for one capacitor and failure-level for another. Always compare against capacitance, voltage class, series, frequency, and temperature.
Typical ESR Values by Capacitor Type
| Capacitor Type | Typical ESR Range | Common Use |
|---|---|---|
| Aluminum Electrolytic (low-ESR) | 0.02 - 0.20 ohm | SMPS secondary/output filtering |
| Aluminum Electrolytic (general purpose) | 0.20 - 3.00 ohm | Bulk filtering and general circuits |
| Polymer Electrolytic | 0.005 - 0.08 ohm | Very low ESR, high ripple capability |
| Film (polypropylene/polyester) | 0.001 - 0.10 ohm | AC, pulse, and snubber applications |
| Ceramic MLCC | Very low, frequency-dependent | Excellent HF bypass; value shifts with DC bias |
| Tantalum | 0.05 - 2.00 ohm | Stable capacitance; derating is critical |
Practical note: for residential/appliance power supplies, ESR drift in electrolytic capacitors is one of the most common root causes of intermittent startup and ripple-related instability.
Fast ESR Troubleshooting Checklist
Compare ESR to datasheet maximum or same-series reference part.
Rising ESR with heat often indicates an aging electrolytic.
High ESR + low capacitance confirms end-of-life in many power-supply failures.
Do not compare ESR across different capacitor types without context.
Frequently Asked Questions
What is ESR in a capacitor?
ESR means Equivalent Series Resistance. It is the small internal resistance inside a capacitor that causes heat and voltage drop under ripple current. Lower ESR is usually better in power supplies.
What is a good ESR for a capacitor?
A good ESR depends on capacitor value, voltage, and application. In switch-mode power supplies, ESR typically needs to be low enough to control ripple and heating. Compare measured ESR to the datasheet or a known-good part of the same series.
What is a typical ESR for an electrolytic capacitor?
Typical ESR varies widely: large low-voltage low-ESR electrolytics can be below 0.1 ohm, while general-purpose high-voltage caps can be multiple ohms. Always judge ESR against part family, capacitance, and voltage rating.
How does ESR affect residential power supply capacitors?
As ESR rises, ripple voltage and internal heating rise. In residential and appliance power supplies, high ESR often causes startup failure, unstable output, or intermittent shutdown after warm-up.