What is the actual ESR of a low impedance capacitor?

Thread Starter

bob2

Joined Jun 15, 2019
102
Hi,
Recently I bought CapXon LZ low impedance capacitors to replace old capacitors. I was a little surprised at the very low ESR.
For example, 1500uF 25v-0.004Ohm.
So should it really be?
 

Thread Starter

bob2

Joined Jun 15, 2019
102
This is an old datasheet, but there is no new one. Even according to the old datasheet, the difference is quite large, four times.
 

Thread Starter

bob2

Joined Jun 15, 2019
102
Always consult datasheet but this gives a general view
General information is good. But I need to at least know max. valid ESR to draw certain conclusions.
In any case, thanks for the information.
 

Papabravo

Joined Feb 24, 2006
12,301
General information is good. But I need to at least know max. valid ESR to draw certain conclusions.
In any case, thanks for the information.
Do you know how to compute the ESR from the dissipation factor (tan δ)?
If not, it gives you the angular relationship between between the real part of the impedance (ESR) and the imaginary part (capacitive reactance). Since capacitive reactance is a maximum for low frequencies approaching DC, I would consider the ESR at 120 Hz. to be a practical maximum value. I'm not clear where the value of 0.004 Ω came from; the value I got was at least an order of magnitude higher. Also for small angles δ ≈ tan(δ) with δ measured in radians.
 
Last edited:

Thread Starter

bob2

Joined Jun 15, 2019
102
I would consider the ESR at 120 Hz. to be a practical maximum value. I'm not clear where the value of 0.004 Ω came from;
And why consider 120Hz, if the datasheets indicate 100kHz?
The value of 0.004Ohm is measured at 100kHz.
 

Papabravo

Joined Feb 24, 2006
12,301
And why consider 120Hz, if the datasheets indicate 100kHz?
The value of 0.004Ohm is measured at 100kHz.
The value of the dissipation factor is given in the datasheet at a frequency of 120 Hz. At that frequency the reactance of your capacitor is less than 1 Ω. The reactance at 100 kHz will be 1.1 mΩ and the ESR will be a small fraction of that. You said you wanted a maximum value.
 

Papabravo

Joined Feb 24, 2006
12,301
I think I see what is going on. 120 Hz. is used for tan δ on components in linear supplies, while those in switching supplies are given an ESR value (a maximum) at 100 kHz. What they don't bother to mention is that the ESR can change over time and might be significantly different at another switching frequency. What I did not realize is that the ESR value may or may not have any particular relation to the nominal capacitive reactance at the stated frequency, which it does at low frequencies.
 
Last edited:

Thread Starter

bob2

Joined Jun 15, 2019
102
I found interesting results on Low ESR capacitors, measured at a frequency of 100 kHz.

Rubycon MCZ 6.3v 1800uf = 1597uf, 1565uf/ 0.009ohm, 0.008ohm
Rubycon MBZ 16v 1500uf = 1414uF, 1401uF / 0.009ohm, 0.008ohm
Panasonic FJ 6.3v 3300uF = 2690uF, 2720uF / 0.004ohm, 0.007ohm
https://www.vogons.org/viewtopic.php?f=46&t=60978
Here I also found very interesting information.
http://phenos.nl/
 
Last edited:
Datasheet.

1500uF not listed but approximating from the supplied data 0.004 isn't too far of the mark.
The full CapXon catalog can be downloaded here: http://www.capxongroup.com/news_in.aspx?lc=1&mnuid=2078&modid=13&nid=271

The LZ series data starts at page 188. Oddly enough, no data is shown for impedance or ESR.

What appears to be the same catalog is here: https://www.wdi.ag/files/manufacturer/capxon/Capxon_Catalogue.pdf

This version of the catalog also shows the LZ series on page 188 and following, and this catalog shows the max ESR at 100 kHz. However, the 25 volt 1000 uF cap is shown as having a max ESR of 20 mohm, whereas the data found by paulktreg shows a max ESR of 18 mohm for that cap, but both data sheets show the same ripple rating of 2180 mA.
 
Last edited:

Thread Starter

bob2

Joined Jun 15, 2019
102
Rubycon MFZ 2700µF 6.3 V 10 mm 20 mm ?0,007Ω ? 105 ? 0.75 € 50 Datasheet not found
http://phenos.nl/
There is a question mark on this capacitor.
Actually the ESR of this capacitor is 0.0045ohm.
This is a very good value, given that he worked for a long time.
 

Attachments

DarthVolta

Joined Jan 27, 2015
76
The value of the dissipation factor is given in the datasheet at a frequency of 120 Hz. At that frequency the reactance of your capacitor is less than 1 Ω. The reactance at 100 kHz will be 1.1 mΩ and the ESR will be a small fraction of that. You said you wanted a maximum value.
so the reactance of a cap is not the same as ESR . I was wondering why some of my calc's were so off. Is that because ESR is a measurement or model that includes inductance and resistance ?

Is there a simple formula for ESR ? I have an LCR meter, I need to lookup how they actually work, and ESR
 

Papabravo

Joined Feb 24, 2006
12,301
so the reactance of a cap is not the same as ESR . I was wondering why some of my calc's were so off. Is that because ESR is a measurement or model that includes inductance and resistance ?

Is there a simple formula for ESR ? I have an LCR meter, I need to lookup how they actually work, and ESR
No it is not. Although the units are the same we are dealing with vectors. In the complex plane at low frequencies a capacitor has a small real real part and a large imaginary part. As the frequency increases the imaginary part goes asymptotically toward zero and apparently the ESR decreases as well for a while.

Check out Figure 4 in the following document for the behavior of ESR as a function of frequency.
https://www.murata.com/en-us/products/emiconfun/capacitor/2013/02/14/en-20130214-p1
 
Last edited:
Top