Author Topic: How to Measure Electochemical Impedance  (Read 1802 times)

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Offline miro123

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How to Measure Electochemical Impedance
« on: October 21, 2022, 07:44:18 am »
  Hello,
I want to measure the electrochemical impedance of mid-size Li/LiFePO4 batteries - 20.....200Ah.
Does somebody knows the circuit to measure it. Any literature on this subject are welcome.

Thanks,
Miro
 

Offline iMo

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Offline miro123

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Re: How to Measure Electochemical Impedance
« Reply #2 on: October 22, 2022, 04:19:22 pm »
Thanks,
It is interesting article describing the basics. The modern manufacture manuals does not describe it.
I posted in metrology section because Solartron Analytical is an market leader in this area.

https://www.ameteksi.com/library/application-notes/solartron-analytical

https://www.ameteksi.com/-/media/ameteksi/download_links/documentations/library/solartonanalytical/electrochemistry/technical-report-06-introduction-to-eis.pdf?la=en&revision=6de3f288-6647-46f4-a102-e25a18beac0b&hash=D48D3BBFA26FE26E28A045AEF2860451

I'm not sure that I posted the topic in correct place. Does  the metrology section discus the modern equipment build from lets say Fluke, Keysight, Solatron or is only their old retro products?
« Last Edit: October 22, 2022, 06:13:58 pm by miro123 »
 
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Offline mendip_discovery

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Re: How to Measure Electochemical Impedance
« Reply #3 on: October 23, 2022, 04:56:53 pm »
I'm not sure that I posted the topic in correct place. Does  the metrology section discus the modern equipment build from lets say Fluke, Keysight, Solatron or is only their old retro products?

No, it is the right place. I just suspect it is a little specialised for just anyone to chime in[1]. I did a google and found some stuff but no more than you could. Most of the stuff I saw referred to test gear you could buy to do the testing and how to use their kit but not much on what that test gear is doing.

At times I suspect the borders between the sections here get blurred. For example, there are plenty of repair threads here and much talk about Test Gear.


[1] I know, doesn't usually stop them.
Motorcyclist, Nerd, and I work in a Calibration Lab :-)
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So everyone is clear, Calibration = Taking Measurement against a known source, Verification = Checking Calibration against Specification, Adjustment = Adjusting the unit to be within specifications.
 

Offline David Hess

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Re: How to Measure Electochemical Impedance
« Reply #4 on: October 24, 2022, 03:27:21 pm »
The major manufacturers of LCR meters and impedance bridges often publish an application note about how to measure impedance in the presence of a DC bias voltage or DC bias current.  This applies just as much to capacitors and inductors as to battery cells.  It is an optional feature on some LCR meters.
 

Offline bateau020

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Re: How to Measure Electochemical Impedance
« Reply #5 on: January 28, 2023, 04:46:17 pm »
Maybe a little late to the dance, but the lowest cost entry into EIS measurements on batteries that I found, is the CN0510 kit from Analog. It needs some tweaking to become more than just a proof of concept though. See my remarks in https://github.com/hb020/batterymeter#battery-equivalent-circuit-model-spectrum-and-the-eis-method

« Last Edit: January 28, 2023, 04:53:21 pm by bateau020 »
 
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Offline trobbins

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Re: How to Measure Electochemical Impedance
« Reply #6 on: January 28, 2023, 09:39:59 pm »
Impedance spectrum assessment was a strong scientific and commercial topic for lead-acid batteries, mainly from a few decades ago when synchronous demodulators and core parts like AD630 became available and lead-acid was the mainstay of telecommunications backup.  There were many papers describing the technique and commercial offerings (such as at INTELEC).  That technique can be at the core of ESR meters, as the ESR of a battery was seen to vary with capacity (and hence used for diagnostic capacity measurement), and with internal aging (and hence also used for maintenance regimes).

I'd anticipate that battery management for Li-Ion has just kept to cell voltage and temperature monitoring and assessment because impedance measurement doesn't add to the base safety and capacity management of a string, and may be very difficult to adequately implement for multiple string situations.
 
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Offline miro123

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Re: How to Measure Electochemical Impedance
« Reply #7 on: January 29, 2023, 09:48:42 am »
Maybe a little late to the dance, but the lowest cost entry into EIS measurements on batteries that I found, is the CN0510 kit from Analog. It needs some tweaking to become more than just a proof of concept though. See my remarks in https://github.com/hb020/batterymeter#battery-equivalent-circuit-model-spectrum-and-the-eis-method
Thanks for sharing. I did not know that such integrated solution exist. the evaluation kit is interesting and has good price

@trobbins - as far as I know EIS meaasuremnts for Lithium baterries is used mainly in three area
  1. Lab tests - requires knowledge of battery internal to read EIS data
  2. Part of SOH & SOC estimators in high end BMS - eg EV BMS
  3. Service - SOH estimators without knowing or les knowing  the history of the battery cells
« Last Edit: January 29, 2023, 10:43:15 am by miro123 »
 

Offline bateau020

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Re: How to Measure Electochemical Impedance
« Reply #8 on: January 29, 2023, 10:11:30 am »
20Ah, and moreso, 200Ah will be a challenge though, depending on the impedance of the batteries. CN0510 is made for impedances that are around the value of RCAL, which is 50 mOhm. If the impedance is significantly lower, you will need adapt RCAL and to increase the current by adapting Q2,R21.Make sure the voltage swing over RCAL remains equivalent to what it is out of the box. I guess one could go down to 5 mOhm.
 
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Offline miro123

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Re: How to Measure Electochemical Impedance
« Reply #9 on: January 29, 2023, 10:37:38 am »
Yes. It need some adjustments. I'm not sure that EVM can shake my LiFePO4 cells - their internal DC resistance is under 1mOhm
 

Offline trobbins

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Re: How to Measure Electochemical Impedance
« Reply #10 on: January 29, 2023, 11:34:54 am »
I've used the AD630, along with IA's and careful design for lead-acid battery fixed and portable impedance work.  Circa 2005 portable equipment had resolution of 0.5uohm, and a 101 uohm shunt was used as part of the calibration, given use on large lead-acid cells.  Sync demod at a non-mains related frequency was needed to cut through the noise from chargers and all sorts of other industrial equipment for on-line tests on battery strings up to 125Vdc with only low injection current of 0.1Arms for handheld device.  The laboratory basis for SOC versus impedance was done with EG&G PAR 273 and 5208 lock-in amp.
« Last Edit: January 29, 2023, 11:44:06 am by trobbins »
 
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Offline trobbins

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Re: How to Measure Electochemical Impedance
« Reply #11 on: January 29, 2023, 11:03:39 pm »
as far as I know EIS meaasuremnts for Lithium baterries is used mainly in three area
  2. Part of SOH & SOC estimators in high end BMS - eg EV BMS
I wouldn't think that was at the cell level within a bulk HV dc string in EV, although I've only quickly looked at Tesla battery tear downs.  For fixed applications based on rack mounted modules, the embedded BMS in circa 20-60Vdc modules I've come across were only cell voltage and temp based, but that was a few years ago.
 


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