BQ20Z65-R1: Modify Full Charge Capacity of gas gauge for system testing

Hello MAtthew,

Full charge capacity is computed by the bq20z65-R1. It is not useful to just change it because the gauge will recompute it at some point based on the data it collected.

If you have a battery in a weird state, then you should take an image of it at that time similar to the "golden image" process. Programming the image will duplicate most issues.

I understand that it will be recalculated eventually after charging or discharging, but I need to leave it in this weird state for at least a few weeks, so that it can be used to verify functionality of software. I know that it is possible to achieve this, I just don't know how we did it in the past (and we no longer have the batteries that we used).

My only thought so far would be to discharge a pack and then recharge it while attaching a programmable DC load directly to the cell stack, causing coulomb counting errors. I forget when and how Qmax is recalculated however, so I'm not sure if this will work.

Hello Matthew,

If you just want FCC to report 1.5x the design capacity, then you could change design capacity to a lower value and reset the gauge. This may do it.

This experiment is not an expected use of the gauge, so your guess is as good as mine.

Unfortunately, the test requires that the battery reports a certain FCC, regardless of the design capacity

Is the formula available for how the calibration values (CC Gain, CC delta, etc) are incorporated into couloumb counting in the bq20z65? Instead of connecting an external load to the cell stack, I could modify the calibration constants of a test battery so that it reads double the charge/discharge current, drastically increase the over charge capacity and then manually charge + discharge the pack so that it learns an FCC that is ~ twice the design capacity. At that point I could restore the original calibration constants and have a battery that is temporarily able to be used for my testing.

Is there any documentation of CC Gain and CC delta? 

I was able to resolve this by cycling the battery after updating CC Gain and CC delta, and then updating Qmax Cell0..3 and Qmax Pack. After resting, the FCC updated to ~2x the nominal capacity upon initiating a discharge (which is what I had wanted).

Great. Thanks for the update.