LFP v’s NCA… and the winner is…

[fhteagle]

 

[AAKEE]

Usually “calibrating” is confirming the starting point for the Coulomb-counting method of determining SOC. If you don’t get into the extreme low or high <20%/>80% the voltage is essentially the same so you don’t really know if you are 50% or 65% SOC as an example as your starting assumption may be out of whack.

The real SOC is not known until after the charging. (except for a full charge where the maximul votlage was held until the current dropped until the pre defined value = 100% SOC. (of course some cells will be lower, and the voltage of these we do not see until we stop charging.

During the end phase of the charge where tesla states "calibrating" there is a flow of current into the battery and the highest cells are held at 4.20V and the descendants are slowly advanging ahead. This will reduce the imbalance in the battery.

Cell balancing is different and is bleeding off the high voltage cells (relatively) to align with the lowest voltage cell. Charge for a bit, then rinse and repeat. This is a lot of the reason charging >80% takes much longer as they have to make sure not to overshoot, rebalance, charge, rebalance…

Active balancing means charging/keeping the cell voltage at 4.20V but draining the high cells, like any better home charger for hobby toys.

Tesla has only passive balancing, that uses resistors to draing the high cells. Mostly performed after the charging session when the car is at sleep. So basically the cell balancing is done after the charging, but still in the last phase of a charge, keeping the cells at 4.20V, the imbalance reduces as there is a higher flow of current to the cells with lower voltage.

 

[AAKEE]

It was a good video.


I just missed one part.

There was not a very clear description about that the car reads and updates the "real" SOC when it is not in use.
The coloumb counting is when driving/charging.

Also, they never discussed the issue that coloumb counting needs a well defined and measured battery capacity (that is correct), otherwise the result of the coloumb counting will be wrong. The part where they discussed the SOC change after a sleep following a drive, they never discussed this issue. Its for sure one of the most frequent reasons to see the SOC go up or down after the drive. Coloumb conting means using the intitial SOC converted to energy in the pack(SOC*estimated capacity) and reduce this with the measured energy/current which gives the new energy on board. Then convert it to SOC again by dividing energy on board with estimated capacity.
If the estimated capacity is not correct, the calculated SOC number will be off - which corrects after a drive when the BMS get the OCV reading.