Do these number suffice to calculate the ESR of this capacitor?

[David_]

Hello.

I have bought 3 10,000µF 35V caps which does not display any ESR in the datasheet.

Well why would I need the ESR for these...?
Mostly for the completeness of my own education and grasp of things.

My LCR meter can only display the capacitance at 100Hz and at 100Hz it shows:

C = 8,8mF
Theta = -84,6 deg
D = 0,096
Q = 10,7
RP = 1,9Ohm

I'm just curios if these values can enable one to calculate the ESR?

Regards

 

[CataM]

Why did you use parallel mode to measure large capacitor?

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Capacitor in parallel with resistance is the same as Capacitor in series with resistance as follows:

 

[David_]

Actually the very last thing I did try was to put the meter in parallel mode just to see what that changed if anything, I didn't even think about the RP parameter and I included it because it was another peace of info I came across.

At 100Hz which is the only frequency where the 10mF(~9mF) is not overloading the range the ESR shows as 0,0Ohm.
Finer resolution does not come until 1kHz, 10kHz and 100kHz.

But are the series resistance the ESR?
It isn't is it?
This touches on the limits of my understanding for AC(impedance stuff)

I am the worst mathematician in the world probably, which is why I ask this question since I am not able to find out on my own.
Seriously you would think its weird how little math I know but I have only had access to my minds intellectual capabilities for some time short of 2 years know. Long story which is just miserable.

But now I have applied to my first math class(in a class room) so hopefully I will be able to make up for lost time and one day be able to converse at the level of others here on edaboard.com about math.

I have tried and tried and tried to learn math on my own on the sometimes Wastefully Wast Web... but I have some real problems grasping the underlying concepts and I think I often am staring the obvious answer right in its eyes without noticing it.

I sometimes feel as I do know a little silly because what good do it do knowing the ESR really...?
its below 0,0Ohm and the application isn't ESR dependant is it. I should read up on that.
(Cap is charged up to a certain voltage and then discharges in a brief window of time which is way shorter than the recovery time, ah yes the ESR determines the voltage drop over the cap does it not...)

Regards

 

[c_mitra]

Capacitor in parallel with resistance is the same as Capacitor in series with resistance as follows:

Obviously something is fishy: the circuit on left has finite DC resistance whereas the circuit on the right has infinite DC resistance.

How they can be same?

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Actually the very last thing I did try was to put the meter in parallel mode

How do you put the meter in parallel mode? I am just curious.

 

[E-design]

You can calculate ESR from this relationship; DF = 1/Q = ESR/Xc

 

[FvM]

You can calculate ESR from this relationship; DF = 1/Q = ESR/Xc

Yes. The exact calculation is shown in post #2.

Obviously something is fishy: the circuit on left has finite DC resistance whereas the circuit on the right has infinite DC resistance.

How they can be same?

They are "the same", or better equivalent, regarding their Q effect, but only for a single frequency.

But are the series resistance the ESR?

ESR spells equivalent series resistance, so yes it is. The question behind is of course, what causes ESR.

As already mentioned, the calculation is only valid for a single frequency. ESR is a frequency dependent quantity, so it can be surely not modeled by a simple series resistor (and neither a combination of a series and parallel resistor). On a behavioral level, you need a RC ladder circuit to model the behavior of a lossy capacitor over frequency.

If you look for physical plausible models, there are different phenomena like electrolyte conductivity and frequency dependent permittivity, double layers, foil resistance and skin effect constituting the observed ESR curve. You'll find some hints in literature, but in most cases it's reasonable to take the ESR as is, trying to measure respectively model it as accurate as required by a specific application.