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NiMH Gas Gauge with a BQ20Z60

Giovanni Marelli
Prodigy 160 points
Other Parts Discussed in Thread: BQ20Z90, BQ2060A, BQ2002D, BQ2002, BQ2000T, BQ2060, BQ29330

Hi, I need help !!!

I'm trying to use a BQ20Z60 based circuit (at the moment I'm working with an "equivalent" BQ20Z90 EVM circuit)  to make a Gas Gauge (and Charge Termination) for a 8S NiMH Battery Pack. The batteries (AA, 2600mAh 1200mV nominal) are connected to the AFE as an equivalent 4 cells pack, with each "cell" made up by two NiMH cells. In this way, I obtain a cell nominal voltage of 2400mV, with COV threshold at 2860mV for a C/10 charging current at 25 degrees and a Timer of 10 hours maximum charging time and 40 degrees maximum Temperature.

I've made various trials to validate the Charge Termination method, and it seems to work quite good (at 25 degrees) ... I don't care very much  if I terminate charging by Cell Overvoltage, Timer, Temperature or Overcharge alarm, without reaching a full charge situation.

The main problem I found is with the Chemistry ID for my NiMH batteries !!!!!!!!!!!!!! The Chemical Updater contains onli LiPo batteries or similar, and I'm afraid that the DOD(OCV,T) table is not good for the real OCV I'm working with ... for example, a fully charged LiPo has a 4200mV OCV, while my "cell" of two NiMH has a 2860mV OCV !!!

I know there are others Gauges (as BQ2060A) which works with NiMH, but I would like to use the BQ20Z60 for many reasons ...

 

Is it possible to develop a Chemistry file with a DOD(OVC,T) table for my topology ?????????????

What should I do ??????????

 

Thanks a lot,

    Giovanni

  • 0
    TI__Genius 10235 points

    The bq20z60 is not intended to be used with NiMH chemistries. The only gauge that supports NiMH at this point is the bq2060A.

  • 0 in reply to Chase7071949597
    Prodigy 160 points

    Thank you, Chase ... I know !!!

    ... but BQ2060A does not manage charge termination ... It only broadcasts an SBS alarm, but I need a gate or an Open Drain output to open a power Mosfet ...

    I know there is BQ2002 family, with the preferred choice of BQ2002D/T for a dT/dt termination of NiMH, but it only supports a C/4 Fast Charge and I need to charge with a slow C/10 charge in my application ...

    Now I'm studying if a BQ2000T + BQ2060A can fit my application, but I have a circuit mounting a BQ20Z90 (replaced with the new BQ20Z60), that I developped for a LiPo application, and it would be very good for me (and for my budget ...) to reuse it !!!!!!!!!!!!!!!

    I only need a .senc file with a working chemistry for my pack, and a precision of 10-15% will be enough for my application ... I can send you t,V,I,T curves of charge and discharge, or tell me the way I can edit a chemistry file, if Texas Instruments let me do it !!!

     

    Thanks a lot,

       Giovanni

  • 0 in reply to Giovanni Marelli
    TI__Genius 10235 points

    The problem is that the gauging algorithm and charge termination(designed specifically for CC-CV) in the z60 is not compatible with NiMH chemistries. A significant firmware change would need to be made in order to make that device work with NiMH chemistries. The Impedance Track devices were designed specifically for LION notebook battery applications. The latest device we have that supports this chemistry is bq2060A. A NiMH charger will need to be used in conjunction for the charge control. Sorry for the inconvenience.

  • 0 in reply to Chase7071949597
    Prodigy 160 points

    Hi Chase !!!

    Thank you for the answer ... I'm quite hard to die, and I'm trying to use the BQ20Z60 (/90) with a Chemistry ID 207 (found with Mathcad tools and a C10 tVIT log) and a BQ2002D as a dT/dt chrge terminator ... it seems to work, but I know that it's an approximation and my QMAX or Ra table may have a divergence ... we will see !!!

    Thank you for the suggestion about BQ2060A ... it's a good choice (but it can't manage FETs and does not have a Sleep or Shutdown mode !!!!!!!!!!!!!!) ... I only have a question for you: bq2060A is supported with the EV2200 interface (RS-232), but I have an EV2300 interface (USB) ... is it possible to make it work with the 2060 [:-)], or should I buy [:-(] an EV2200 ???

    Thank you for the help,

       Giovanni

  • 0 in reply to Giovanni Marelli
    TI__Genius 10235 points

    The bq2060A will only work with the EV2200, unfortunately.

  • 0 in reply to Chase7071949597
    TI__Expert 7230 points

    The BQ2060 can control both charge and discharge FETs.

    Pin 15 DFC - Discharge FET control

    Pin 16 CFC - Charge FET control

  • 0 in reply to Keith Keller
    Prodigy 160 points

    Thanks Keith !!!

    ... but DFC and CFC pins are intended for use as Lithium Pack protectors (they are based on Cell Voltage measurements), but not for use with a NiMH pack as in my application. From the datasheet I can't found an application where CFC is pulled down in the case of a dT/dt charge termination or DFC is pulled down in the case of Pack Undervoltage ...

    Maybe I should use the bq2002D/T for charge termination and "feed" Vcell1-4 from my battery pack (unuseful for NiMH ...) or with a resistor network for a discharge Cell Undervoltage ... but the real question is ... will CFC and DFC be driven by the internal state machine when the bq2060a will recognize a NiMH chemistry ??? I didn't found an answer in the datasheet !!!

    Thank you for the help,

       Giovanni

  • 0 in reply to Chase7071949597
    Prodigy 160 points

    OK Chase ... I'll buy an EV2200 ... :-( !!!

    If I send you some tVIT log files (Charge C/10 - C/4, Discharge C/10 - C/5 - C/2) could you build me a new chemistry file ???

       Giovanni

  • 0 in reply to Giovanni Marelli
    TI__Expert 3865 points

    bq2060A is CEDV device not a z-track device. It doesn't use any chemistry files. You will need to run set of learning cycle in order to set the CEDV parameters using Mathcad though.

    Follow the app note SLUC042 (do a keyword search from TI website).

  • 0 in reply to Jackie Hui
    Prodigy 160 points

    Thank you, Jackie !!!

    But I need chemistry files for Gauging with a bq20z60 ... I'm working with a chemID 207 and a resistor network from the pack and feeding the VCELL inputs of the AFE (bq29330) as a two-series 4,2V (LiPo) batteries. It seems to work and I'm collecting a lot of Charge end Discharge Cycles at different loads and charging currents ... I don't need a 1% error for my application ... 10-15% will be enough ... And don't care about charge termination: I'm going to use a bq2002D/T with a dT/dt termination.

    I'm only asking to Texas if anyone can build me .chem files (bq20z60) for my NiMH (a new ID) from my tVIT logging files !!!!!!!!!!!!!!!!

    I would like to use a bq20z60, because it fits much better my application needs than a bq2060A !!!!!!!

       Giovanni

  • 0 in reply to Giovanni Marelli
    TI__Expert 3865 points

    The z-track devices only support Li-ion battery. It's NOT a matter of creating a chem file or not. bq20z60 doesn't support NiMH. You have to use bq2060A for this chemistry.

    If your accuracy requirement is only 10-15% on the NiMH project, you can get away by using fix EDV on bq2060A. In that case, you only need to run a full discharge at room temp with normal current. Calculate the 7%, 3% and 0% points, input the voltage levels to EDV2,1,0 and configure bq2060A to Fix EDV.