Reference Guide

Typical ESR for Electrolytic Capacitors: What's Normal?

You measured ESR on a capacitor. Now what? This guide gives you practical reference values so you can tell the difference between a healthy capacitor and one that's about to fail. Includes typical ESR ranges by capacitance and voltage band.

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What Is ESR and Why Does It Matter?

ESR (Equivalent Series Resistance) is the real, resistive loss inside a capacitor. In an ideal capacitor, ESR would be zero. In practice, every capacitor has some ESR from the leads, foil, terminal welds, and — in electrolytic capacitors — the ionic resistance of the liquid electrolyte.

Why ESR matters:

Power dissipation

P = I²rms × ESR. Higher ESR = more internal heat = shorter life.

Output voltage ripple

V_ripple = I_ripple × ESR. High ESR increases noise on power rails.

Filtering effectiveness

A capacitor with high ESR can't filter effectively at high frequencies.

Health indicator

Rising ESR is the earliest measurable sign of capacitor degradation.

Typical ESR Values by Capacitance & Voltage

These are approximate values for standard aluminum electrolytic capacitors measured at 100kHz, 20°C. Low-ESR series will be significantly lower. Values increase with age and temperature.

Rule of thumb: if your measured ESR is more than 2–3× these values, the capacitor should be replaced.

Capacitance	10V	25V	50V	100V	250V	450V
1 µF	8.0 Ω	10 Ω	12 Ω	15 Ω	—	—
10 µF	3.0 Ω	3.5 Ω	4.0 Ω	5.0 Ω	8.0 Ω	—
22 µF	1.8 Ω	2.0 Ω	2.5 Ω	3.0 Ω	5.0 Ω	—
47 µF	1.0 Ω	1.2 Ω	1.5 Ω	2.0 Ω	3.0 Ω	5.0 Ω
100 µF	0.5 Ω	0.5 Ω	0.7 Ω	1.0 Ω	2.0 Ω	3.5 Ω
220 µF	0.2 Ω	0.25 Ω	0.3 Ω	0.5 Ω	1.2 Ω	2.0 Ω
470 µF	0.10 Ω	0.12 Ω	0.18 Ω	0.3 Ω	0.7 Ω	1.2 Ω
1000 µF	0.05 Ω	0.07 Ω	0.10 Ω	0.18 Ω	0.4 Ω	0.7 Ω
2200 µF	0.03 Ω	0.04 Ω	0.06 Ω	0.10 Ω	0.25 Ω	0.5 Ω
4700 µF	0.02 Ω	0.02 Ω	0.03 Ω	0.06 Ω	0.15 Ω	—
10000 µF	0.01 Ω	0.015 Ω	0.02 Ω	0.04 Ω	—	—

Note: These are typical values for general-purpose electrolytic capacitors. Low-ESR series (designed for switching power supplies) will have ESR values 2–5× lower than shown here. Always check the specific datasheet for exact ESR specifications.

What Affects ESR?

Capacitance Value

Inverse relationship

Higher capacitance = lower ESR. Larger capacitors have more electrode surface area and more electrolyte, reducing resistance.

Voltage Rating

Slight positive relationship

Higher voltage = slightly higher ESR. Thicker oxide layer adds to dielectric resistance. However, the foil is often larger too, partially offsetting this.

Temperature

Inverse relationship

Cold temperatures increase ESR dramatically. At -40°C, ESR can be 5–10× higher than at 20°C because the electrolyte becomes more viscous.

Frequency

Inverse (up to resonance)

ESR decreases as frequency increases (up to a point). At very high frequencies, ESL (inductance) becomes dominant instead.

Age / Hours of Operation

Direct relationship

ESR increases over time as electrolyte dries out. This is the most important factor for predicting remaining life.

Capacitor Construction

Design-dependent

Low-ESR series use better electrolyte formulas and thicker electrodes. Polymer electrolytic capacitors have the lowest ESR of all electrolytic types.

Interpreting Your ESR Meter Readings

Good

ESR is at or near the typical value for its capacitance/voltage.

Action: No replacement needed. The capacitor is healthy.

Suspect

ESR is 2–3× higher than typical. Capacitor is aging.

Action: Plan for replacement. Monitor more frequently. May still work but life is reduced.

Failed

ESR is more than 3× typical, or reads open/shorted.

Action: Replace immediately. The capacitor is causing circuit problems (ripple, heat, instability).

ESR Frequently Asked Questions

What is the typical capacitor in residential power supply capacitance and ESR?

Many residential/appliance power supplies use electrolytic capacitors from about 10µF to 470µF on secondary rails, and larger bulk capacitors on primary sections. Typical ESR depends on value and series, but low-ESR secondary capacitors are commonly well below 1 ohm in healthy condition.

What is ESR in a capacitor?

ESR stands for Equivalent Series Resistance. It is the total internal resistance of a capacitor, including the resistance of the leads, foil electrodes, terminal connections, and — most importantly in electrolytic capacitors — the ionic resistance of the liquid electrolyte. ESR is measured in milliohms (mΩ) or ohms (Ω) and is always present in every capacitor.

What is a good ESR reading for a capacitor?

It depends on the capacitance and voltage rating. As a rough guide: a 1000µF/25V electrolytic should have ESR below 0.1Ω. A 100µF/25V should be below 0.5Ω. A 10µF/50V should be below 3Ω. If your reading is more than 2-3x the typical value for that capacitance/voltage, the capacitor is degraded and should be replaced.

Does ESR change with frequency?

Yes. ESR is frequency-dependent. Most ESR specifications are given at 100kHz. At lower frequencies (like 120Hz for mains-powered circuits), ESR is typically higher. This is because the electrolyte's ionic resistance is more dominant at lower frequencies. Always check at what frequency the ESR spec was measured.

What causes ESR to increase over time?

The primary cause is electrolyte drying. As the liquid electrolyte slowly evaporates through the rubber seal, its ionic conductivity decreases and ESR rises. Higher operating temperatures accelerate this process. Excessive ripple current also generates internal heat that speeds up electrolyte evaporation.

How do I measure ESR?

Use a dedicated ESR meter or a multimeter with ESR function. A regular multimeter in capacitance or resistance mode cannot measure ESR. The capacitor must be discharged and removed from the circuit (or at least one lead disconnected). ESR meters apply a small AC signal at a known frequency and measure the resistive component.

What is the difference between ESR and impedance?

ESR is only the resistive (real) part of a capacitor's opposition to AC current. Impedance (Z) includes both the resistive part (ESR) and the reactive part (capacitive reactance and inductive reactance). At the capacitor's self-resonant frequency, impedance equals ESR because the reactive components cancel out.

Why do "Low ESR" capacitors cost more?

Low-ESR electrolytic capacitors use higher-conductivity electrolyte formulations, thicker foil electrodes, and improved terminal connections. These materials cost more but allow the capacitor to handle higher ripple currents with less internal heating, which directly extends operating life. The premium is usually worth it in power supply applications.

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