Electrolytic capacitor ESR not specified in datasheets, can it be estemated?

[David_]

Hello.

I am looking to buy some 10µF electrolytic capacitors and while reading the datasheet:
**broken link removed**

I can't find any info about impedance or ESR, I do know that I do not necessarily need to know that about this cap. They will be used as general purpose decoupling paralleled with a low capacitance ceramic capacitor but still, I wonder if the one page datasheet provided above gives any info that one can use to estimate ESR or impedance at some frequency?

If you can't view PDFs the info given is:
Capacitance: 10µF.
Voltage: 63VDC.
Tolerance: ±20%.
Voltage: 79VDC(Surge).
Rated Temperature: 85C(-40/+85C).
Leakage Current: 6,3µA.
Leakage Condition: 2Min/20C.
Dissipation Factor: 9%.
Current/Ripple Current: 70mA(120Hz 85C).

What interesting parameters can I(If any?) calculate with those characteristics known?

Regards

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BY the way, ESR sounds as if it would concern DC current/voltage while the capacitors impedance would be more appropriate to consider in AC circuits?

 

[d123]

Hi!

Some links that might help:

The Wikipedia one gives some typical values for different dielectric types. The WIMA one has a reasonably acceptable formula you can use to calculate it (not sure if it only applies to plastic film though). The "low esr" pdf has some horrendous looking formulas - if you're good at maths that isn't an issue!

https://en.wikipedia.org/wiki/Equivalent_series_resistance

https://www.wima.com/EN/dissipation.htm

https://www.wima.com/EN/dissipation.htm

 

[Warpspeed]

What interesting parameters can I(If any?) calculate with those characteristics known?

Probably not much, because ESR and impedance versus frequency are strongly related to manufacturing methods and the physical internal construction.
If you are really concerned, it really needs to be measured.

If its a critical application, you should be using the more expensive low ESR electrolytics, which will be fully specified.

Normal aluminium electrolytics, particularly the lower cost Chinese variety are probably fine for less demanding applications.

 

[KlausST]

Hi,

pleas use complete KEMET ESK type datasheet:


then select "ESK" form the Quick Datasheet Link

But unfortunately there is no ESR value given. But the ripple current and dissipation factor.
Since the values are given for 120Hz it seems it is no high frequency electrolytic capacitor.

I don´t recommend to use it at frequencies higher than 1kHz.

Klaus

 

[d123]

No favourite brands, but Panasonic (www.panasonic.industrial.com) are pretty thorough in the descriptions of their capacitors on the main pages, before you even get to the pages for specific series, and each online datasheet gives esr values (besides all the other important values), I'm using their high ripple aluminium electrolytics for filtering, and use their web to figure out what I need and which available is within those parameters.

 

[chuckey]

How about dissipation factor, loss R/XC = 9% which does not look impressive. Also the ripple current ^2 X ESR = power dissipation, so depending on the case size a guessimate of max power (.5?, 3? , 5watts?), so again an approximation of the series loss resistance can be calculated.
Frank

 

[D.A.(Tony)Stewart]

Re: Electrolytic capacitor ESR not specified in datasheets, can it be estimated?

Ripple voltage at low frequency is governed by the ratio of source to load impedance. The Caps are distributed in parallel with the source voltage impedance. Regulators have a low ESR that is reduced by the DC feedback gain , which rises to the internal ESR and distributed ESL with frequency due to gain-bandwidth of the regulator if used. otherwise an unregulated source has the ESR each part in series, ( winding Rs, diode pair ESR, and any series R,L impedance.

The Caps are rated at 120 Hz since a bridge doubles the line frequency. The D or δ = tan δ for low values is simply the ratio of ESR/Xc where Xc = 1/(2pi*120Hz*C[F].

So you can calculate ESR = D*2pi*120*C

The max ripple current(rms) is given with an internal temp of 85'C so you can compute the device thermal resistance if you wish using 60 deg C rise over Power dissipation (Irms²*ESR) .

If there is a switched or dynamic load RL with a capacitive or inductive load and associated ESR's you can estimate the ripple voltage from the ratio of load ESR * I step. This ripple is reduced by the often same or lower ESR ceramic caps at a frequency between the SRF of the e-cap and the ceramic caps.

Often this is overlooked and designers will either over-design it ... Or under-design it and fix it later with low ESR caps and/or LC filters and/or RF caps and/or distributed dielectric C in the PCB substrate.

So it all depends on your dynamic step current, ripple requirements on which components you choose in a design.