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BQ34Z110: ChemID match help for BB EVP35-12 35Ah Sealed Lead Acid VRLA AGM Standard Type

Part Number: BQ34Z110
Other Parts Discussed in Thread: GPCCHEM, , BQSTUDIO, BQ34Z100-G1

Hello,

Is anyone available to help with a ChemID match?

Target Battery Pack is 24V comprised of two BB EVP35-12 35Ah Sealed Lead Acid VRLA  AGM Standard Type batteries in series.

I can provide the data sheet if needed.

I'm ready to obtain the discharge data needed to search for a ChemID match per Thomas Cosby's Chemistry ID Selection Application Report.

I have a battery analyzer to control the C/10 discharge rate and log the V,I,T data w/ 1s sample rate with CSV file output.

I'm thinking this would be better than using the EVM adapter which doesn't provide for external Temp measurement.

If a log file generated using eqEVSW is preferred it's no problem.

Please advise regarding cell termination voltage, and if for ChemID match purposes, a  discharge test of a single 12V battery is preferred over the 24V pack.

Thank you in advance.

  • Hello Rom,

    You should follow the GPCCHEM guide in order to collect the data and submit it to find the best match. If your battery is already characterized in our database you can use the matching chem ID.

    Any method to collect the data specified in the guide is ok to use.

    It would be better to test with a single pack in series instead of 2 packs.

    Sincerely,

    Wyatt Keller

  • Thank you Wyatt for putting me on Track.

    I'll test one 12V PbA pack as you suggest and set NumCellSeries=6

    A few questions after reviewing the 2018 GPCCHEM guide.

    The 5s-100s sampling interval range called for is much more liberal than the 1s given in Thomas Cosby's 2013 report.
    What would you suggest for PbA with 35AH capacity?

    I understand the intial charging portion is not required.
    For PbA with 35AH capacity, is it acceptable to commence logging shortly prior to Full Charge Cut-Off?
    i.e. a small number of samples collected prior to Full SOC.

    I'm not clear on the <0.1% range accuracy called for in the current measurement.
    For the Fig 1 example,the current range is bound by +4300ma in Charge -2750ma in Discharge.
    Is the current measurement resolution called for 7.05ma or 2.75ma?

  • Hello Rom,

    I would focus on the guide for GPCCHEM tool, this is written by the creator of the tool. I don't have much experience with Tom's guide.

    You can include additional data in the log, as long as you have a long relax, discharge at the specified rate, then another long relax the tool should work. I would not include any additional data after the discharge and relaxation period, like another charge cycle.

    A current accuracy from a 15-16bit ADC designed for measuring current through a sense resistor should be fine, most customers use our gauges to collect the current. If you have a Maccor or Arbin battery tester this data can also be used.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    I will use the EVM module then for the measurements with 5s sampling.

    I understand additional charge data is okay.
    But I'd like to know where I need to start measuring.
    The GPCGHEM guide only provided Fig 1 to discern this.

    I made a mistake in my last post reading the Fig 1 example for data collection in the GPCGHEM guide.
    If I'm reading the charge profile correctly this time, the CC rate is 1300ma @ 2hrs  followed by CV at 4200mV @ 4hrs.
    I can't see where the charging ends and the relaxation period begins.
    I would expect to see a small current step here, followed by a 2 or 5 hour relaxation period depending on chemistry.

    If I am to use this Figure as a guide, I would begin collecting data about 2 hours prior to the CV charging stage.
    Then allow a 5hr relaxation.
    Agree?

  • Hello Rom,

    The log file should contain a minimum of 5hr relaxation after charge and before discharge. Then after the discharge completes it should contain approximately 5 hours of relaxation. This is defined in the guide, section 3.4 PbA/Lead-Acid.

    https://www.ti.com/lit/pdf/SLVA725A

    The figure can be used as a guide, but the CC/CV rates are not important since it depends on the battery being used.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    I understand the CC/CV values are charger & chemistry dependent.

    The confusion is that the figure in the guideline shows the CC/CV periods.

    Are you saying the CC/CV periods of charging are not required?

  • Hello Rom,

    The tool does not actually require the charging data. All it needs is a fully charged, relaxed battery that is discharged to minimum and relaxed again. It suggests this profile/time period because you want it to be freshly charged and relaxed (you wouldn't want to use a battery that has self-discharged for too long). I suggest logging everything because you can always remove sections if you don't need them and it can help if you have issues.

    I know PbA can be a bit different to Li-ion in terms of charging, so just make sure the pack is fully charged and relaxed before you discharge.

    Thanks,

    Alex M.

  • Thank you very much Alex!
    I understand what is needed and why.
    I'm sure others would benefit by adding your input to the next doc update.
    Many Thanks,

    Rom 

  • FYI Alex,

    I came across this figure from  SLYP822 ,pg 10 for consideration in the next update to SLVA725A.
    It clearly shows the required relaxation period following the charge.

    Page 10 from TI Fuel Gauges Step By Step Guide to Production Presentation Slides slyp822.pdf

  • Hello Rom,

    Yes, you do need the relax at the beginning, re-reading my post, I can see I wasn't very clear on that. In that document, the sections you need are the two relaxation periods (in blue) and the discharge (in yellow). In addition, it gives instructions on how to charge it, but the tool doesn't actually need that. 

    Thanks,

    Alex M. 

  • Hello Alex,

    Yes, this figure clearly shows the end of charge, where the charge voltage is removed and marks the onset of the OCV relaxation period.


    Specifically, does the data collected require at least 1 sample prior to the first sample of the OCV relaxation period?
    If not,  when the charger indicates a full charge, I would simply swap the battery connects from charger to the EVM within the 100s sample rate interval called for in SLVA725A.  Then I don't have to worry about the charger exceeding the EVM current sense spec.


    If at least one sample is required prior to the onset of OCV , then the charger would need to be connected to the EVM.
    In this case, how many hours or minutes of sampling is required prior to the onset of OCV?
    This will allow me to determine if  the maximum charge current in the capture window might exceed the EVM spec on the current sense resistor.

    In consideration of putting the battery in the best full charge condition for the purpose of the ChemID selection, what is the preferred charging rate for Lead-Acid chemistry?  The guide mentions C/20 as an example taper current, but doesn't suggest a charge current rate.

    Many Thanks,
    Rom

  • Hello Rom,

    That piece of overlap showing the taper is likely just a mistake from the drawing of the box. Ultimately, the tool isn't so sensitive. I ran a profile today that had multiple charge and discharge cycles and it still worked. I also ran one that started when current was 0 with none of the charge tapering and it worked as well. You can always log more and delete the sections you don't need. 

    The cell manufacturer should specify a charging profile. Here is a page on PbA batteries that talks about some of these details. It seems to vary quite a lot from 0.3C to 1.5C, so I would defer to the cell manufacturer. Also, the GPCchem guide does suggest 5 hours of relaxation after charge instead of the 2 hours for li-ion. 

    As long as a CV taper is done, the battery should be fully charged, and after relaxing, ready for discharge for the tool. Because of this, the CC rate isn't actually very critical. 

    Thanks,

    Alex M.

  • Hello Alex,

    Thank you for running some tests.
    When you say the tool works, does that mean it has what it needs for an accurate ChemID determination?


    Since the charging rate affects internal battery heating, I would think it important, unless the ChemID matching algorithm compensates for temperature.
    This leads to the question, how important is the cell temperature measurement accuracy?
    Since I'll be using the BQ34Z110 EVM for the measurements, is it recommended to remove the thermistor and apply it to the battery case with RTV?
    Should the battery, with thermistor attached, be enclosed in a container as in most end-use applications?

    The battery manufacturer specification for the nominal capacity is for a C/20 discharge rate, but a nominal charge rate is not provided.
    The manufacturer does provide a typical example profile with CC rate of 0.1C for cyclic use.  They also provide performance data for higher rates. The Battery University reference says 0.3C for fast charging.  A nominal CC charge rate is not given in the GPCchem guide.
    Is fast charging recommended for this test? 

    The battery manufacturer also doesn't provide the taper current level used to switch from CV to float charge - i.e. the full charge point and the onset of the OCV relaxation required for the test.   The chargers I have, one charging at 0.3C and the other at 0.05C both use 0.01C to switch from CV to float charge,   The Battery University reference gives 0.03C-0.05C.

    Shouldn't testing use the same charge rate and taper current level as that used in the ChemID database for PbA?
    Can you find out what it is?

    Many Thanks,

    Rom

  • Hello Rom,

    That is correct, it will have enough data to make accurate chem ID matches.

    The gauge uses the charge efficiency parameters to help adjust for heat loss. For the chem ID the charge portion is not critical since it is trying to match the chem ID which is using the discharge to find the best DOD vs OCV curve match. It is important to charge with a small enough taper in order to fully cycle the battery, but the tool is mostly looking at the relaxation and discharge period.

    The temperature of the battery is important and should be attached to the outside shell of the battery as close as possible to the cells.

    It is not critical for the taper rate to be the same, as long as the starting DOD points are close for the tool to match the proper chem ID. I would use the smaller taper charge if possible to get a fully voltage range of the cell.

    I would also recommend upgrading to the BQ34Z100-G1 since this gauge has support for lead acid cells and it uses the newer BQStudio and EV2400development platform.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    Thank you very much.
    I'm clear now on all test set-up parameters except thermal considerations in testing large batteries.


    Note that the target 12V Lead-Acid sealed battery is 8"L x 5"W x 6"H and weighs 25 lbs.
    I didn't find anything this large in the ChemID list for PbA and so I wonder about the battery size effect.

    If we consider 5 sides of a battery cube exposed for ambient cooling, a 4" cubic battery would have nearly twice the surface area to volume of an 8" cube. Then the larger battery would run hotter with comparable thermal heating density..

     
    Are you getting ChemID matches of large PbA batteries without requiring anything special in the test to compensate for battery size?

    Sincerely,

    Rom

  • Hello Rom,

    The tool mostly looks at the OCV matching when finding the best fitting chem ID, temperature will have some affect on the results, but with the low discharge currents used for the chem ID matching process the internal heating should have minimal impact.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    I see, thank you.
    I'll submit the test data for matching shortly.

    Sincerely,

    Rom

  • Hello Wyatt,

    Should the data log file be formatted as shown in the GPCCHEM Guide?
    It shows only labels comma delimited, followed by data space delimited and with no wrap?
    Or is the format exported from a spreadsheet as CSV acceptable?

    Thanks,

    Rom

  • Hello Rom,

    As long as it is comma separated it should be fine, if you have an Excel and export it as a CSV it should correct the formatting.

    You can open the file in notepad and double check if it is only comma separated to make sure.

    Sincerely,

    Wyatt Keller

  • Thank you Wyatt.

    Rom