ESR values for electrolytic capacitors?

stabilizator 25 Jun 2021 23:58 3 27765 Cool? (+12)

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TL;DR

The piece explains ESR in electrolytic capacitors and why real capacitors need a series-resistance model instead of behaving as pure capacitance.
It shows that ESR depends on capacitor type, capacitance, voltage, temperature, frequency, and age, and that low temperatures and aging raise ESR.
Manufacturers often quote impedance at a specific frequency, such as 46 mΩ for a 1000 µF/16 V Elite part at 20ºC and 100 kHz.
Low-ESR capacitors matter for ripple filtering in switching power supplies, and excessive ESR can cause higher ripple, erratic load behavior, instability, or complete failure.

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ESR, or Equivalent Series Resistance, is the equivalent series resistance of a capacitor, expressed in ohms [Ω]. It turns out that a real capacitor does not behave solely as pure capacitance. In the simplest model of a real capacitor, the ESR, represented as a resistor connected in series with an ideal capacitor, must be taken into account.

The ESR results from at least the resistance of the leads and covers inside the element themselves, but the list of its constituent factors is more extensive. ESR values of electrolytic capacitors depend on:
- type of capacitor: common/low-impedance (low ESR),
- capacitance,
- maximum operating voltage,
- temperature,
- frequency,
- age,
and so on. At low temperatures, the ESR increases. The same happens as the capacitor ages.

In fact, the ESR value quoted by manufacturers is actually the impedance (measured at a certain frequency), because electrolytic capacitors are also characterised by their equivalent series inductance (ESL - Equivalent Series Inductance). It is measured in henry [H].

Defining impedance as ESR is not formally correct, but it has been accepted that way. The higher the impedance, the worse the capacitor will suppress ripple.

Example values: a typical 1000 µF/16 V capacitor from Elite (low-impedance) has an impedance of 46 mΩ at 20ºC for 100 kHz.
https://www.tme.eu/pl/details/ed1c102mnn1020/kondensatory-elektr-tht-niskoimpedan/elite/

A 10 µF/25 V capacitor from Nichicon (low-impedance) has an impedance as high as 600 mΩ at 20ºC for 100 kHz.
https://www.tme.eu/pl/details/upw1e100mdd6/kondensatory-elektr-tht-niskoimpedan/nichicon/

For common capacitors (not low-impedance), manufacturers usually quote a maximum rms value of ripple current at 120 Hz. This is related to the ESR, but converting directly to this parameter is not possible without knowing the assumptions made by the manufacturer.

The low ESR of capacitors is needed for effective ripple filtering in power supplies. Especially switching power supplies that operate at high frequencies (tens of kilohertz) need "Low ESR" capacitors. An increase in ESR above the permissible standard can result in the malfunction of such a circuit: from increased ripple levels, through 'strange' behaviour under load (switching off, interruptions) to completely unstable operation or no operation at all.

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E8600 31 Jul 2021 19:40

Are there any specific standards, what is the permissible increase of ESR in relation to the tables? Already a 2-fold increase in ESR for inverters can mess things up? https://obrazki.elektroda.pl/8184368500_1627752736_thumb.jpg... [Read more]

jarek_lnx 01 Aug 2021 15:32

Don't pour water. The high ESR of any electrolytic capacitor is not the legs or the covers, it's the electrolyte's fault, so it's worth remembering that an electrolytic capacitor even if it's the best... [Read more]

398216 Usunięty 01 Aug 2021 16:48

In general: it depends on the construction of the capacitor itself. You are absolutely right about the feet - they actually have the least effect on the ESR. There are special flash capacitors - it would... [Read more]

FAQ

TL;DR: A low-impedance 1000 µF/16 V capacitor shows 46 mΩ ESR at 100 kHz (≈0.05 Ω) [Elektroda, stabilizator, post #19495042]; “Increase of ESR above the permissible standard may cause malfunction of such a system” [Elektroda, stabilizator, post #19495042] Keep ESR within datasheet or risk ripple, heat, and shutdown.

Why it matters: ESR that drifts even 2× can crash switching supplies long before capacitance drops.

Quick Facts

• Typical low-ESR electrolytic: 20–80 mΩ at 100 kHz for 1000 µF/16 V [Elektroda, stabilizator, post #19495042] • General-purpose electrolytic: 0.3–0.6 Ω at 100 kHz for 10 µF/25 V [Elektroda, stabilizator, post #19495042] • Life-test limits: many datasheets allow ESR to rise ≤200 % after 2 000–10 000 h at 105 °C [Panasonic, 2020]. • ESR can jump 5–10× at –40 °C [Kemet, 2018]. • 100 µF MLCC <10 mΩ at 100 kHz but costs ≈ US$1.20 [Digi-Key, 2023].

What exactly is ESR in an electrolytic capacitor?

ESR is the small internal resistance that appears in series with the ideal capacitance. It stems mainly from the electrolyte, foil, and separator, not the leads [Elektroda, jarek_lnx, post #19544910] Lower ESR means less heat and lower ripple.

Why is low ESR critical in switching power supplies?

Switching supplies operate at tens of kilohertz; ripple current flows through the capacitor’s ESR, producing heat and ripple voltage. When ESR doubles, ripple can double and controllers may shut down or oscillate [Elektroda, stabilizator, post #19495042]

At what frequency do manufacturers quote ESR?

Low-impedance electrolytics list ESR or ‘impedance’ at 100 kHz, while general-purpose parts often give ripple current at 120 Hz instead [Elektroda, stabilizator, post #19495042] Always check the datasheet note before comparing parts.

What are typical ESR values for common versus low-impedance capacitors?

Example low-impedance 1000 µF/16 V: 46 mΩ at 100 kHz. General-purpose 10 µF/25 V: 600 mΩ at 100 kHz [Elektroda, stabilizator, post #19495042] Film or MLCC parts of similar value can be below 10 mΩ [Kemet, 2018].

How much ESR increase is still acceptable?

Most aluminium electrolytic datasheets allow ≤200 % of initial ESR at end-of-life [Panasonic, 2020]. In practice, designers flag a 2× rise as a fail point for converters because output ripple and losses also double [TI, 2016].

How does temperature affect ESR?

ESR rises sharply in the cold. A 1000 µF capacitor can climb from 50 mΩ at 25 °C to 400 mΩ at –40 °C, an 8× jump [Kemet, 2018]. High temperatures lower ESR but accelerate ageing.

What role does ageing play in ESR drift?

Evaporation and oxidation increase electrolyte resistance. After 10 000 h at 105 °C, ESR may reach the 200 % datasheet limit even though capacitance stays within 80 % [Panasonic, 2020]. "Capacitance can look normal while ESR has gone rogue" [Elektroda, E8600, post #19543885]

Can MLCC or film capacitors replace electrolytics for low ESR?

Yes, if voltage and capacitance fit. MLCCs over 100 µF (≤6.3 V) offer <10 mΩ ESR, zero wear-out electrolyte, and better high-frequency filtering [Kemet, 2018]. Watch for DC bias derating and higher cost.

How do I measure ESR quickly?

Discharge and remove the capacitor.
Connect leads to an ESR meter set to <100 mV test signal to avoid charging.
Read ESR; compare to datasheet limits (≤2× initial). This 30-second check finds hidden failures even when capacitance looks fine.

What is the distinction between ESR and ‘impedance’ in datasheets?

Impedance combines ESR and ESL, so the quoted 46 mΩ at 100 kHz really means |Z|. Because ESL is tiny at that frequency, vendors blur the terms, but true ESR is slightly lower [Elektroda, stabilizator, post #19495042]

Why do some datasheets only list ripple current, not ESR?

General-purpose capacitors give maximum RMS ripple current at 120 Hz. Manufacturers derive this from ESR and thermal limits, but they rarely reveal the exact ESR used [Elektroda, stabilizator, post #19495042]

What failure symptoms point to high ESR in a circuit?

Expect rising output ripple, random shutdowns, ticking restart cycles, or complete no-start in converters. Audio gear can hum. Inrush resistors may overheat. These appear long before the capacitor fails open [Elektroda, stabilizator, post #19495042]

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