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bq78pl114 firmware support for high current/capacity cell

Evgen Urlep
Prodigy 30 points
Other Parts Discussed in Thread: BQ78PL114, BQ76PL536

Dear sir,

We are intending to use bq78pl114 to manage 160 Ah battery cells LiFePo4 from ThunderSky TSLFP160AHA (Voltronix).

Is possible to obtain chemistry files / make own chemistry setup of that cell type?

Discharge currents 3C are beyond 480 A (Current application will support up to 300 A discharge currents).

Are there any firmware limits preventing the usage of the bq78pl114 in this current region?

The current measuring shunt has too high voltage drop therefore we intend to add operational amplifier to increase shunt voltage drop gain.

What needs to be modified in the setup if it is even possible or we just use gain constant to nominal capacity/current treshold?

Is there a possibility to incorporate thermal coeficient constant of the measuring shunt to the measuring algorithm in the firmware.

Thank you for the answers, Evgen

 

  • 0
    Intellectual 372 points

    IMHO the 300A DC current sensing is better handled using hall sensors like these: http://www.hallsensors.de/

    Then you do not need any instrument class op-amp.

  • 0
    Prodigy 70 points

    Hello

    I m using the Thundersky bms to give me some information about the battery pack, but it´s very limited , so

    I´m also thinking in using the bq78pl114 to manage 160 Ah ThunderSky batteries , and I have the same problem

    because in my aplication I have 30s1p , and currents that can go up to 800A , a current shunt it´s not a good option,

    I whould like to use hall sensors but them I will have a problem interfacing with the bq78pl114 .

    Other problem is because I,m using 30  160Ah cells , I will have to use at least 3 bq78pl114 , do I need 3 current  measurements

    or connecting all 3 bq78pl114 , I only need 1 currnent measurement ?

    best regards

     

  • 0 in reply to Celso Menaia
    Intellectual 372 points

    To connect a single bq78pl114 to a hall current sensor one way is to use an isolated DC/DC converter to supply the sensor, and using a simple resistor network to interface the current sensor output to the bq78pl114 current shunt inputs.  There are several details that must be worked out, like noise, sensor power consumption etc., but the main problem is to reflect that current signal to several bq78PL114. 

    So instead, unless your requirement absolutely need active balancing, I would suggest using five bq76pl536 (datasheet: http://focus.ti.com/lit/ds/symlink/bq76pl536.pdf). They are designed for these kind of applications.

     

  • 0 in reply to Per Hassel Sorensen
    Prodigy 70 points

    Hello  PerBear

     

    thank for your answer.

     for now I will go for the BQ76PL536 solution, and after I get my prototype up and running , I can think about active balance.

    were can I get the full size reference schematics for the bq76pl536 ?

    thanks for you time, best regards

     

  • 0
    TI__Intellectual 1940 points

    Regarding chemistry files:  If the cell type does not already have a Chemistry ID (CHEM ID) and associated .chem file, then the cells will need to be sent to the BMS Applications team in Dallas to have them characterized.  This can take up to several weeks depending on factors like cell type and test lab queue.

    Current Measurement Range:  Use of a 0.0005 Ohm sense resistor on each bq78PL114 is really approaching the practical limit of the device and circuit topology.  Other users have hinted at this.  Current and capacity reporting uses SBData protocol.  Current is limited to +/-327.680 Amps and capacity figures are limited to 655.35 AHrs.  Both would use IPScale = 0001 as described in SBData's SpecificationInfo() command.

    Stacking:  Each bq78PL114 will require a sense resistor.

     

  • 0 in reply to Jim M15252
    Prodigy 30 points

    Thank you for your answers.

    We are currently in the phase of design, therefore trying to avoid future pitfals.

    Is it feasible to incorporate low power operation amplifier to increase gain (G=2) in current measurement, therefore enabling use of lower shunt values?

    What would happen if the scaling factor is set wrong (in purpose)  therefore firmware thinks the current is only half of the actual value.  The capacity using coloumb counter would count half of the actual or can be there another issue. We are aware that the current measurement accuracy is lower and short current protection could be slower. That two factors would double current measurement range in my opinion to cca. 650 A.

    What is the closest chemistry to the Thundersky 160Ah AHA (previous mentioned) to support the application.  When disabling impedance tracking seems the chemistry file not so critical. Setting the chemistry parameters seems to be the biggest problem at this approach. Is there a better description for that, or is it not to be revealed? What is the approximate cost when sending the battery to the BMS applications team (email: evgen@piktronik.com)?

    Is there a possibility to disable active charge pump, and selecting only passive or just replacing charge pump inductances with resistances?

    Is there a possibility to update firmware/seting the parameters using third party download software (customer-developer), since we intend to communicate with the larger networed system using CAN, therefore USB-TO-GPIO seems to be limiting option. It would be wery hard to tweak the parameters in case of a problem, when the batteries are scattered thousands kilometers around. Will be the SMBus protocole revealed for this solution?

    Best regards, Evgen