bq20z65 unsuccesful golden cycle attempts

I am working with a bq 20z65 fuel gauge. I have been attempting to run a golden cycle on the pack according to the instructions "when a close Qmax is not known in SLUA 334B".

From what I observed so far it looks like the Vok flag resets about 4 hours into the relaxation time after charging the pack. But there does not seem to be any change in the output voltage.My understanding is that for Qmax to update the Vok flag must be set. 

Is there a setting in the gg file that could affect this or cause this to happen?

  • I'm not sure what you mean when you say you aren't seeing a change in output voltage. There will be no change to voltage. All the VOK indicates is that there was a valid OCV reading and FCC should change some. Qmax won't change until step 7.

  • In reply to Chase7071949597:

    Sorry for the confusion this is a bq20z45R1 I am having trouble with.

    Even though I have cycled it through all the steps listed in the instructions in 334 I have never been able get a Qmax update. The Max error stays at 100%. The Vok flag resetting described earlier was just an observation I thought might help.

     I don’t see anything happening that would prevent Qmax from updating.

    My temperature and voltage is ok, the delta capacity looks to be good. Not sure about offset error though.

  • In reply to Mark Gaugenmaier:

    Make sure you are getting at least 90% of Qmax and the Design Capacity out of the battery during the charge cycle. When entering the intial Qmax and Design Capacity in to the gauge, use the datasheet minimum instead of the max or typical. This is the most common reason for not getting a Qmax on the initial learning cycle. Did you happen to make a log file of the learning cycle using bqEVSW? If not, please do this on your next attempt.

  • In reply to Chase7071949597:

    I am using Valence IFR 18650 cells and the datasheet only gives a nominal capacity of 1350mAh @ C/5 discharge rate. So that is the value I used. (Should I try a lower value to start with?)After the charge portion of the golden cycle the capacity read 1243mAh.

    I am enclosing the data I took for your review. There are several log files because I stopped the logging after the initial discharge and continued the testing the next day. Also I had some communication issues between the computer and EV2300. It did not affect the cycling but I had to restart the data logging a few times. The files are named in sequence from step 1 to step 5 due to the logging restarts. The testing spanned from 3/12/2012 to 3/14/2012. After the initial discharge the pack relaxed from approx. 22 hours. After the charge the pack relaxed for approx. 21 hours. After the discharge data logging continued for another day.

    I also included the inital gg file I used for the cycling that I created from the bq easy page in the eval software.

    Thank you

     

     

  • In reply to Mark Gaugenmaier:

    Hello Chase,

    Were you able to receive my log files from my last post?

    I inserted them but I'm not sure that it took them.

  • In reply to Mark Gaugenmaier:

    The files don't appear to be attached. The 1243mAh should be enough to allow an update, so there must be something else.

  • In reply to Chase7071949597:

    I tried to insert the files again and the function does not seem to work. Is there another way to send my files?

    I zipped them up and the size is 719k.

  • In reply to Mark Gaugenmaier:

    Don't use the Insert File button. That doesn't seem to work. If you look up above the reply there are three links,  Compose | Options | Preview

    Select Options and then you can Add the file from there.

  • In reply to Mark Gaugenmaier:

    Yes, they are there now.

    Do you know what the cause of the communication issues are? The problem is that if there is a legitimate power loss or reset in the gauge, then the learning cycle won't work. There needs to be a continuous rest of 5 hours after enabling Impedance Track and then also after the subsequent charge in order for the Qmax update to work. The passed charge requirement is being met and I don't see anything else in the log file that would prevent the update from working.

    Also, it appears that the battery is being overcharge (OC flag is set in Charging Status). That could also be causing problems.

    Would it be possible for you to redo the learning cycle while following the procedure below and capturing everything in one log file? Try not to overcharge the pack if you can (I calculated you got about 1450mAh out). Also, on the discharge, don't discharge below the CUV threshold. In step 7, change the relax time to 5 hours instead of 2.

    One more thing; can you verify the chemistry ID you are using? I see you are using LiFePO4 cells, so the wrong chem ID could also be preventing Qmax updates.