Battery Impedance Measurement - ESR

[ogden]

For example, this EIS scan:
https://www.researchgate.net/figure/EIS-curves-of-lithium-ion-batteries-with-different-SOC-and-maximum-discharge-capacities_fig1_313830344

shows how cells 1, 2 and 3 give almost same (within 5%) Zre between 5kHz to about 1Hz but then the curves differ significantly, some 50-70% difference in Re below about 0.1Hz.

If you make the decision at Z_1kHz, you completely miss the fact they behave so differently at the frequency range actual loads use.

Those are ESR measurements at different state of charge at different frequencies. You are so obsessed about SOC here   I am looking for a way to easily estimate and compare current handling capacity of batteries of the pack - when they are fully charged obviously. This thread feels like broken record where I say: I want to use it for A but you say no it can't be used for B

[edit] EIS for 3 cells attached. Took from article. Two healthy cells and one inferior. It is clear that impedance of one cell is worse through whole frequency range. Guess which one is inferior. Other graph do not need any comments.

[ogden]

Maybe 1kHz AC ESR is somewhat useful, maybe not; show me. Despite common Internet advice, it isn't some magical "this is how it's done professionally" word of God

LOL. I don't know who you think you are. Fact is that battery 1KHz AC ESR meters are manufactured by many reputable manufacturers, many industries uses such. Just one example of various choices https://www.tequipment.net/battery-testing/ Note that many capacity meters have ESR mode as well.

[trobbins]

Ogden, do you mind tempering your self-righteous comments please.  This forum and thread is for the wider community, and for years to come - its not just all about you.  You didn't start the thread, so there is no requirement from other posters to align to your view on this topic, or to get chastised by you.

[Jay_Diddy_B]

Hi,
When I started this thread I wasn't thinking about the large battery arrays that are used in data centers, telecom, off grid storage and similar applications.

I was thinking about 18650 cells that widely available from old laptop batteries and that are often sorted and repurposed by the community.

If you are tasked with managing a battery array in a data center, you can probably justify having a tool like the Fluke BT510.

If you are sorting discarded cells a cheaper, simpler alternative is probably more appropriate. I took my capacitor ESR meter and modified for 1 kHz operation. I have used this technique to find high impedance cells that will not take a charge. You can build this for about $10-15, less if you have a good stock of parts.

I don't have a data center or any off grid storage. I don't have any lead acid batteries apart from the one in my car. So I have little use for a Fluke BT510 or similar.

It is a question about the right tool for the job. A Keysight 3458A is a great multimeter in the lab, but it is not very handy if you are troubleshooting a car. A low cost handheld is probably much better.

The small signal measurement of ESR is probably useful some of the time, but not all of the time and not all applications.

Regards,
Jay_Diddy_B

[floobydust]

What did the test current end up being for your modified ESR meter? I am I right seeing the measurement output is 10mV=100mohm.

Hioki Lead-acid Battery Tester Test current is 160mA for the 3mohm and 30mohm ranges, 16mA for 300mohm range, 1.6mA for 3ohm range.
HP 4328A Test current is 150mA for the 1mohm, 50mA for 3mohm range, 15mA for 10mohm range, 1.5mA for 100mohm range.

[ogden]

I was thinking about 18650 cells that widely available from old laptop batteries and that are often sorted and repurposed by the community.

Yes, exactly. Same here. In first message I said measure ESR of batteries "up to certain capacity" because it is obvious that your tool can't reach low ESR of the big batteries anyway. Some forum members are trying to derail whole idea by all means. I mentioned hi-end tools only to prove that standard (IEC 61960-3:2017) 1KHz AC battery measurement is widespread and it works.

[ogden]

What did the test current end up being for your modified ESR meter? I am I right seeing the measurement output is 10mV=100mohm.

Hioki Lead-acid Battery Tester Test current is 160mA for the 3mohm and 30mohm ranges, 16mA for 300mohm range, 1.6mA for 3ohm range.
HP 4328A Test current is 150mA for the 1mohm, 50mA for 3mohm range, 15mA for 10mohm range, 1.5mA for 100mohm range.

It is +/- 1.2mA. Note LTspice simulation provided in this post.

[Siwastaja]

Ogden, do you mind tempering your self-righteous comments please. 

Ogden's always like that. Quite often he happens to be right, sometimes he's not, sometimes he even "stands corrected" (which is great, and which was the reply I was expecting to see opening the thread), but all in all, the process of "internet fight about who's right" overriding the desire to understand and gain knowledge is very, very tiring, especially when you know what you are talking about, have done it for years, and have spent some time to think about it, then certain people can't go beyond level of "lol your stupid".

This time, I just don't have time and energy to participate to this "I said that, you said that, no I didn't say that, you cherry-picked that, you misread my graph" shitstorm. It's great this forum has the ignore feature; good riddance.

Please feel free to utilize or ignore my expert opinion.

[ogden]

When self-proclaimed experts will understand that this thread is not about ideal battery meter, but modification of JDB 100KHz ESR meter to measure batteries without losing it's elegant simplicity - then perhaps we may talk. Meanwhile "I know it better" trolls are free to live happily in their self-importance bubble and dream about their perfect battery testing tools. Others are welcome to discuss how to improve _simple_ battery ESR meter JDB is offering in another thread, if it needs any improvements at all.