I’m using Batrium CellmonK9 with Lifepo4 16S. Ist there a way to calibrate the cell voltages in the software.
If shunt voltage shows 54,8V I would expect an average of 3,425V at the cells. In theory such a setting should give us a nice value for balancing >3,42V at the cells.
But it is not. The sum on Cell voltages is approximately 0,35V (350mV) below the shunt voltage.
Measured by multimeter the shunt is right and each cell voltage is ~ 0,022V (22mV) below readings.
I have the same issue. The multiplication of the bypass voltage with the number of cells just is not enough for the external charging voltage to reach the bypass voltage at least for a single cell (if all cells are almost equal in voltage). External voltage needs to be 0,4V at minimum more to get the bypass starting at all. To get all cells beyond bypass voltage 0,5V more charge voltage than multiplication voltage is required. Is this discrepancy normal? Or is this by accident or by intention that additional voltage that Victron Energy for example uses to feed in DC PV excess.
Request to have the calibration of the CellMate-K9 on the software:
Thanks for the recommendation. This feature is something that our team will work on when we get the chance, in the same manner, that this can be done on the other existing individual cell monitors.
Please know that balancing at 3.425V all the time is bad for a whole bunch of reasons. See below:
The passive balancing cell modules are not designed to balance all the time, they will not last long term.
At this voltage, the calibration can have adverse effects on the battery’s SoC as it will be thinking to adjust things when the battery is ok to start with.
At this resting voltage of 3.425V there is a really wide SoC% range and so picking this value and thinking this is right and adjusting accordingly is suboptimal and will have adverse effects.
The suggested recommended practice of above 3.55V is the recommended balancing when full. Running substantially lower will give false outcomes.
Please know that Auto Balance is not recommended for LiFePO4.
We have an additional extra balancing mode for LiFePO4 that will document soon, this works to continue to run the bypassing process when any cell reaches the bypass threshold (i.e. 3.5v), to continue even after charging has stopped for a period of time even after the battery returns to 3.425V when the charging pauses. This means that the capacity of that cell can be reduced when charging resumes, allowing other cells to catch up and will repeat the same cycle until all have achieved the balancing voltage. This works far better than cell voltage matching when not full or empty. Once the pilot has been completed we will publish the new method Latched mode soon.
Calibration adjustment at 22mV is within the 0.5% tolerance of the product and pushing beyond the calibration reference of the equipment and then hence even tighter than the LiFePO4 recommended operating threshold (see above list).