Other Parts Discussed in Thread: BQ34Z653
Hi Everyone,
I am having a persistent issue whereby the gas gauge often incorrectly changes the capacity of the battery, rendering all information about the battery's state of charge useless.
In the graph below shows the results of running 5 charge/discharge cycles of my 84600mWh battery over the course of a few days.
Raw Data: Copy of BM2_cycle_test.xls
The cycle looked like this:
1. Charge until taper current is reached
2. Rest for 30mins
3. Discharge until the low voltage threshold is reached
4. Rest for 30mins
5. Repeat 5 times
While the Voltage plot mirrors this cycle nicely the Relative State of charge plot does not reflect this at all, with significant clipping below what it perceives to be 0% and it never reaches full capacity because of that offset. Additionally the maximum SOC reached each cycle decreases, indicating that the the full charge capacity is being recalculated incorrectly every cycle. Following the experiment the Full Charge Capacity of the battery is 163770mWh, much larger than what it should be.
The current and voltage measurements are calibrated to within +/-10 mA/V just before the experiment and those calibrations are still accurate following the experiment.
This is an issue I have seen many time during the development of this battery, while this is the highest full-charge capacity measurement that I have seen, I have seen values as low as 17000mWh. The problem also persists between battery packs so it is not device specific.
This problem is wreaking havoc on all state of charge measurements such as relative state of charge and time to empty and is rendering these completely useless.
Is this a problem that other people have come across and may have a solution to?
Thanks, David