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BQ40z60 and BqStudio Charging/Discharging

electronicjohn
Intellectual 330 points
Other Parts Discussed in Thread: BQSTUDIO, BQ40Z60, BQ40Z60EVM-578, EV2400

I have the bq40z60evm board connected to an EV2300 and a 12V lab power supply for VAC.  BqStudio seems to be reading the voltages properly and the battery health correctly, but I can't for the life of me get it to charge or discharge, even if I turn on the CHG/DSG FET's.  I also am a bit confused about running the learning cycle calibration since both manual and automated modes specify they need external relays.  Any advice in the right direction would be useful!

  • 0
    Prodigy 80 points

    +1 here, I'm in the same boat.

  • 0 in reply to Vlad Ardelean
    Intellectual 330 points
    While we wait for any more knowledgeable people do you have any theories Vlad? For the discharging I suspect maybe we actually need a load of some sort to drain the power into, but this doesn't make sense for simply charging the battery. The pertinent registers seem to be:

    ACFET (1 so it's good)
    ACLW (0 so the AC voltage is high enough)
    FET_EN (1 which I believe is right)
    CHGR_EN (1 which I believe is right)
    CHG/DSG (both 1)

    My only idea is that CC doesn't seem to go high for me even when I try to use the CHARGER_ENABLE command. Also, ChgM seems to stay high even when I try writing to it to be 0. This means manual charging and since I want the bq40z60 to control charging internally I've been trying to set this to 0, but to no avail.
  • 0 in reply to electronicjohn
    TI__Guru 73830 points
    John and Vlad,
    I am sorry for the slow response, but the question was posted to the wrong forum. The bq40z60 belongs to the gauge group. It looks like you have all of the FETs enabled to support charging. You mentioned that you cannot get the pack to discharge and that you are having problems with the Learning cycle feature in bqStudio. Can you get charging and discharging to work at all? I am not sure that the Learning cycle feature works, so it would probably be better to just run the cycle manually. How many series cells do you have in the pack? The device is configured for 3S, so you will need to configure some charging parameters to support 2S or 4S. If you can export a gg..csv file, then I can help to review your setup.
    Tom
  • 0 in reply to ThomasCosby
    Intellectual 330 points

    My bad, I've been confused about where to post the bq40z60 since it is both a charger and a gauge. I'll post questions on there for now on regarding it.  I haven't managed to get charging/discharging to work at all, and I haven't tried the learning cycle using bqStudio yet since this first step hadn't been obtained.  I will be able to generate a gg.csv file first thing tomorrow, but the battery I'm using is a 3S like the default for this gauge.  

  • 0 in reply to electronicjohn
    TI__Guru 73830 points
    The screenshot shows that the FETs are on, so you should be able to discharge by placing a load across the VSYS to PGND ports on terminal blocks J1 and J5. Some probing will be required, if you cannot discharge as something must be broken.
  • 0 in reply to ThomasCosby
    Prodigy 80 points

    Thanks for the reply Tom,

    Same as John, I got confused, I considered the bq40z60 as a charger + gas gauge not as a gas gauge + charger. 

    I still cannot make the discharge path to work. Here's my setup:

    Boards: EV2400 + bq40z60EVM-578

    VAC to PGND input voltage: Lab power supply, 18.2VDC @3A max.

    Batteries used: LiFePO4, 2P2S configuration, type ANR26650M1-B, 2500mAh per cell, selected chemistry ID 0x0440.

    The battery pack is connected with the negative at J3.1N.

    Although I don't care about the cell balancing feature, I did connect J3.1P between one of the two series cell groups.

    The battery pack's positive terminal is connected at J3.2P+3P+4P (shorts between 2P, 3P and 4P).

    Jumper J4 is at 2S.

    I can get the manual charging to start, but it does not stop at 7.2V, the voltage keeps going up, which makes me think either my configuration profile is wrong or the Chemistry ID is not right, so I had to turn it off when the voltage on the cell pack reached 7.2V.

    I have a 68ohms/5W load connected between VSYS and PGND. During manual charging (I mean if I hit the CHARGER_EN button from the COMMANDS panel), I measure 8.52V across the load resistor (VSYS to PGND is 8.52V). 

    I can never get the discharge fet to turn on. If the battery is not being charge, VSYS stays at 0, I can never get the battery voltage on to VSYS no matter what I do.

    My gg.csv file is here: https://www.dropbox.com/s/5yfzqd4grx37jyg/LiFePO4_Config_1.gg.csv?dl=0

    Thank you kindly for all the help and support!

    Vlad

  • 0 in reply to Vlad Ardelean
    TI__Guru 73830 points
    Vlad,
    Your DA Configuration register is still setup for 3S. You will need to change it to 01 and this should take care of the CUV fault and allow the DSG FET to turn on. You need to send the FET_EN command, instead of using the manual FET control commands to enable the FETs, You also need to enable IT (GAUGE_EN).

    Your Minimum Voltage Output is set to 3650. I calculate that it should be set to 4214 for a 2S configuration.

    Tom
  • 0 in reply to ThomasCosby
    Prodigy 80 points
    Looks like it is working! Thank you so much!

    Vlad
  • 0 in reply to ThomasCosby
    Intellectual 330 points
    Thomas,

    I wasn't shorting 4P to 3P and that was causing my problem. Once I connected it to 3P I started charging and discharging successfully! I do have a couple questions though:

    1. you said learning cycle may not work, and I would have to do it manually? How would I go about this? Right now when I had GAUGE_EN=0 the battery life was aroung 50% but turning on GAUGE_EN dropped it to 29%. Is this due to the calibration not being completed yet?

    2. Right now I only have the balance terminals connected. It seems like the charging/discharging should primarily go through the thicker two leads of the battery. Is it right to say we just connect these two leads to the 1N and 3P/4P terminals?

    3. Is it possible to power the load directly while also charging the battery? I have a power resistor connected between VSYS and PGND for my load. I noticed when I enable charging the total current coming from the power supply is the same when charging the battery with the power resistor connected and disconnected. I would expect the total current to go up if it was both charging the battery and powering the connected resistor.

    4. Is it possible to power the load without also charging/discharging the battery? It seems like when I disable charging the power to this is completely cut off from both the battery and the main power supply (since ACFET turns off).


    Thanks for all the help!
  • 0 in reply to ThomasCosby
    Prodigy 80 points

    Hi Tom,

    I implemented the changes (DA config to 2S, min volt out to 4124, enable IT) and the charging voltage was correct (7.2V), the discharge started to work great,  but it stopped at 5.8V instead of 4.4V (I have a 2S2P LiFePO4 pack) and obviously, I can no longer turn the discharge on.

    My CUV Threshold is 2200mV, CUVC Threshold is 2400mV and Recovery for both CUV and CUVC are 3000mV.

    How can I get the discharge to go all the way down to 4400mV for the 2S pack?

    Vlad

  • 0 in reply to Vlad Ardelean
    TI__Guru 73830 points
    Vlad,
    I tested your srec and was able to discharge until the cells reached the CUVC threshold of 2400mV. Can you provide a log file showing the discharge and when the DSG FET turns off?

    Tom
  • 0 in reply to electronicjohn
    TI__Guru 73830 points
    John,
    The cells should be connected together with very short low impedance straps to minimize voltage drops across contacts. The connections from the cells to the gauge should be kelvin (effectively no current) connections where the device can get a true cell voltage measurement and not one from a drop across a wire. The kelvin connections for BAT+ and BAT- should be at the cells and not at some point along the copper trace.

    You can power the load with the charger. You will leave the CHG and DSG FETs on and current will be supplied by the charger as long as the charger current is sufficient. If the load current exceeds the charger current, then current will also be supplied from the cells.
    Tom
  • 0 in reply to ThomasCosby
    Intellectual 330 points
    If J3 is solely for the cell kelvin connections where is it that the charging/discharging pins of the battery are connected? Connecting the positive terminal of the battery to VSYS seems wrong, and the pcb file for the bq40z60 eval board shows thicker traces on the 4P pin of J3, and the current sense resistor is between 1N of J3 and PWR_GND, but your response makes it sound like the charge and discharge pins should NOT be connected to this connector. Can you clarify?

    Also, is it possible to power the load with the charger when a battery is not present? It seems like I can occasionally get current to flow from the charger to the load in this case, but it is not consistent.
  • 0 in reply to electronicjohn
    TI__Guru 73830 points

    The J3 connector is not strictly used for kelvin connections on the EVM. The cell connections for 1P, 2P, 3P are, but the connections for 1N and 4P will be high current. There are kelvin connections on the PCB to support these terminals. You would not connect the battery to VSYS. The gauge/charger are not designed to power the load without the battery present. I have also had some success when using a resistor divider network on the cell inputs, but I have seen stability issues.

  • 0 in reply to ThomasCosby
    Prodigy 80 points

    By all means, please see attached. I went through a charging cycle followed by discharge. The discharge stopped at around 5.6V on the cell pack (VSYS was turned off at this point).LiFePO4_Logs_1.zip

  • 0 in reply to Vlad Ardelean
    TI__Guru 73830 points
    Vlad,
    It looks like one of your cells may be bad. Check the Cell 1 voltage in Column AU in the discharge log. It crosses the CUVC threshold and disables the discharge.

    Tom
  • 0 in reply to ThomasCosby
    Prodigy 80 points

    LiFePO4_2S2P_Dump_2.gg.zipAlso, please see attached my current data memory file.

    Thanks!

    Vlad

  • 0 in reply to ThomasCosby
    Prodigy 80 points
    Yup, that makes total sense!

    Thank you!