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BQ27441EVM-G1A: SOC doesn't exceed 60%

Cédric
Prodigy 40 points
Part Number: BQ27441EVM-G1A
Other Parts Discussed in Thread: GPCCHEM, BQSTUDIO, EV2400

Hi,

I developped a program in order to initialise the bq27441.

I have modified the specifics settings like asked in the datasheet :

> Design Capacity (DC) : 3300

> Design Energy(Dnrj) : 12210

> Terminate Voltage(TVolt) : 3200

> Taper Rate(TR) : 330

However, my RM never reach the maximal value (3300) when the battery is full. It maximal values match with 60% of the DC. Also, when SOC reach 0% my battery is not empty.

For exemple, when my battery is full, I have 1724 as RM value and 3107 for Full Available Capacity value.

When I decrease the value of DC, the RM value decrease too and it's not logical.. I think that the RM value must be the same!


Hypothesis:

> When my battery charging, it is disconected from the bq27441, it's a problem?

> My battery is an Lithium-Polymer Battery, Need I to modified something for this?

Thanks,
Cédric

  • 0
    TI__Guru* 76230 points
    Hi Cedric
    These symptoms are indicative of not using the right chem id. The gauge you are using is a ROM gauge with fixed chem ids. Before using these type of gauges with your cell, you need to perform a rel-dis-rel test as listed in gpcchem to identify a close chem id match for the cell. In your case, you are using a rom gauge so you have to check to see if the hard coded chem ids are a close match for your cells. If they are not, then you will have to choose a flash based gauge. The report which the gpcchem tool will send you will let you know how close of a matcth the internal chem ids in your gauge are to your battery.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 40 points

    Hi Onyx,

    Thanks for your answer, it's already a first step for the resolution of my problem!

    If the chem id are saved in ROM, I cannot added another chem_ID? It's that you said with the using of a flash based gauge?
    But it's not possible to modify my gauge now, may I modifiy several settings in order to approch the most perfect behaviour for my cell ? Whichs?

    Currently , I don't have device to get data from my cell and thus use gpcchem.

    Thanks,
    Cédric.

  • 0 in reply to Cédric
    TI__Guru* 76230 points
    Hi Cedric,
    Yes you cannot program a different chem id on the gauge other than what is hard coded.

    The rel-dis-rel test does not require any special equipment. You just need to have the evm and bqstudio to log data. Connect a power supply as your charger and then an electronic load. Charge the cells to full, relax two hours, discharge to empty, relax 5 hours. Then submit the log file to gpcchem and it will identifiy a matched chem id for your cells and tell you how much deviation the hardcoded chem id is from your cell.

    pls read through the instructions in gpcchem manual. It is basic and straight forward.

    if it so happens that you the hardcoded chem ids are not a close match, and it isn't possible to change to a flash based gauge, then i am afraid you will have high gauging inaccuracy.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 40 points
    Hi Onyx,

    I will look at to use bqstudio with the evm module (EV2400) but with my current architecture, I cannot examine with the bq27441 my cell when this is charged. Will it make a problem for the rel-dis-rel test ?

    Thanks,
    Cédric
  • 0 in reply to Cédric
    TI__Guru* 76230 points
    hi Cedric,
    i am not sure i understand what you mean by you cannot examine the bq27441 with your cell charged. how and why is that?

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 40 points
    Hi Onyx,

    I have integrated bq27441 device on a specific card where the battery charge is extern.
    When I want to charge my LiPo battery, I need to unplung the cell from the bq27441.
    So, my bq2741 device cannot seen the charge of my cell and it's not possible to modify this architecture.

    I wondered if I need to buy/developp another card with the bq27441 for the rel-dis-rel test or if it will possible with my current architecture ?

    Cedric.
  • 0 in reply to Cédric
    TI__Guru* 76230 points
    You can either purchase a gdk which has an onboard gauge to do the rel-dis-rel or you buy a bq27441 evm. You need the charge portion of the rel-dis-rel to identify a chem id.

    thanks
    Onyx