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Battery Management - Gas Gauge Forum
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.
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.
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.
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.
Were you able to receive my log files from my last post?
I inserted them but I'm not sure that it took them.
The files don't appear to be attached. The 1243mAh should be enough to allow an update, so there must be something else.
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.
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.
I believe the files are attached now.
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.
One more thing. It appears that Cell 4 is quite imbalanced from the other 3 cells. It reaches charge terminate voltage more quickly and the CUV threshold much more quickly than the other 3 cells. You may want to look at that and make sure the cell isn't damaged or aged somehow.
The communication issue was most likely caused by another program periodically opening up on the computer I was using. The golden cycle was never disrupted during charge or discharge. The communication loss fornutately only happened during the relaxation periods. Also there were no power losses during the cycling. Tomorrow I am setting up another computer to run the cycling on.
I am using chem ID 0404 which closely matches the discharge curve shown in the data sheet for these cells. The discharge curve is very flat. I could not find a chem ID specifically for the Valence IFR 18650 cells. Do you have a chem ID for these cells?
The datasheet calls out 3.65 volts for the full charge voltage. There are 4 cells in series so I'm charging it to 14.4 volts at 675mA and and shutting off charge at 68mA taper current as the data sheet suggests. Should I raise the taper current up to prevent overcharge? What would you suggest?
I am discharging at 270mA and cutting off discharge at 9.8 volts. The data sheet calls out min voltage per cell to 2.5 volts. I can raise the cut off to 10 volts.
One other thing, I saw that the gg file calls out the CUV Threshold at 1700mV. Is this too low for a cell that the min voltage is rated to 2.5 volts?
Can you send command 0008 to address 00 and then read back from the address? This will show us the chemistry ID. The reason I ask is becaus the default Ra table in the GG file you sent doesn't match the default Ra table for ID404.
As for your cell, it doesn't look like we have ever characterized. The main concern you will have is potential accuracy issues by using the wrong ID. The typical process for cells is to send a few samples to TI and we characterize them and create a new ID. The process for LiFePO4 cells takes about 4 weeks. ID 404 is the correct type of chemistry, however, so if accuracy is acceptable once you get your learning cycle going, then we don't need to create a new ID for you.
Your charge and discharge settings appear to be fine, then. I think we first need to figure out what ID is in the gauge.
I believe I sent you the wrong gg file.
I may not have made a copy of the file with 0404 before we cycled it. But I just confirmed the ID to be 0404 with the 0008 command and I know the pack has not been disturbed since it was cycled. I exported the gg file and attached it for your review.
I am also ordering a fresh set of cells to eliminate the weak cell.
I just completed another golden cycle. The data is attached. I included two copies of the gg file. One was exported just before cycling and the other copy was exported after cycling. I used brand new 18650 cells (IFR Valance same kind as last time). The chem ID is 0404. I followed the instructions "when no close Qmax is known" in your previous post. I am using the 20z45R1 TI EVM board for the cycling.
The Max Error is still at 100%, so Qmax did not update. Please take a look at the data and see if you can see anything that might be causing the problem.
I also need to do golden cycling on the 26650 version of these cells but I haven't started that until I can resolve the issue with the 18650 version.
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