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Battery Management - Gas Gauge Forum
bq78PL116EVM Aux file logging
Three questions regarding .csv file data logging:
1. Do I need to keep polling and logging during my overnight cell rest period.
2. Is there a recommended chemistry file for modern generic Chinese hobbyist LiPos? I'm using chem 107 (the newest default?) with a 7s1p 10Ahr battery.
3. Should I stop logging to avoid the rebound of cell voltage, where the DFET turns back on after cells rest for ~15 minutes (next rebound is after about 2+ hours).
1) It depends on why you are collecting data. If you are collecting data to support aux file generation or to monitor parameters, then you do need to poll all night. You do not have to poll continuously during the rest period to keep the part running, etc.
2) We do not recommend using this device with LiFePO4 cells. It has some limitations in the minimum cell voltage and special simulation features needed to support these cells. It is not impossible to use the device with these cells, but it will take some parameter tweaking to get good results. The PL900 and separate fuel gauge may be a better fit.
3) Logging should not affect cell rebound performance. You will need to let LiFePO4 cells rest for a very long time to allow them to stabilize to make an accurate Qmax update. The rest periods will need to be at least 6 to 12 hours.
Thanks for the reply.
With regard to 1. are you saying that I have to keep polling and logging data all night (16 hours) while the cell is resting? Except for Excel file size and the computer/EVM going south I am puzzled by the popup I always get asking me for a comment, upon re-opening the logging session. This kind of implies that I can continue with the data collection. I am collecting data in the .csv file for Aux file generation.
With regard to 2. slua505b p. 12 says:
1=Sanyo:18500 UR18500F (1700mAh)
IIRC, somewhere I saw that this is the new default chem file. The previous one was:
My problem is that I'm using generic LiPo cells, nice 10Ah ones, to make a 7-cell battery for test of the bq78PL115, and I'm wondering if chem ID 107 is my best bet. As usual, the distributor has no idea who makes them, but he does have performance curves. I figure the EVM can determine all the curves it needs.
With regard to 3. I'm using LiPo, not LiFe. I have found that I overlooked a requirement in one of the aux file generation documents that says to totally stop the discharge for the rest period, which I guess means not to let it bounce even slowly, as contrasted with chatter, which it disallows explicitly.
Must I log a resting battery for 16 hours while making a csv file for aux file generation?
Is Chem ID 0100 or 0107 recommended for generic LiPo?
I can't tell you how happy I am to find such great support from TI. Thanks again,
Sorry for the confusion over LiFePO4. It is difficult to say which ChemID to choose for the analysis. An incorrect selection can cause the aux file parameters to be off. If they are off a little, then the device can compensate and refine Qmax and the Ra-table in subsequent learning cycle runs. But, it it is off too much, then the device may not be able to compensate and make a good prediction. It would be better to find a part number for the cells to look up a ChemID.You can always rerun the aux file tool and choose a different ChemID later, if you do not get good performance results with the first try.
You should not need a 6 to 12 hour rest time for LiPo cells. You can stick with the recommended 2 hour rest times.
The aux file generation tool does need data to be logged during the rest periods. You can stop and restart logging, but you should leave logging enabled when collecting data for the aux file tool. Don't worry about the pop-up message. You can ignore it.
You mentioned that you are using 10Ah cells. You will probably be using a 5A discharge, since you have a 1P configuration. But, I should warn you that the aux file tool has an undocumented limitation. The charge or discharge current cannot be greater than 10A.
You should be able to save your .csv file to some location other than the desktop. I usually place it on the desktop, because it is convenient to find later.
I'm involved in a BMS project for 7s11p configuration and 24.2Ah. With the bad news that aux file tool has the limitation of 10A, this means that Aux file data collection procedure will not work beacause C/2=12.1A and 0.7C=16.94A.
There is another way to solve this problem? it is planned soon a new release of the aux file tool ? We plan to start with the aux file tests in about 1 month.
You can either use a smaller charge and discharge current or an IPscale = 10 setting to collect the data for the tool. We do not plan to modify the aux file generation tool.
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