FAQ: Voltage adjustment for SBM

Question: I checked the datasheets for the SBM product. I think the over voltage and under-voltage does not fit my needs.  Can over and under-voltage levels be customized for lifepo4 cells? I think that 3.9 volt over and 2.0 volt under protection voltages are too high/low.

Answer:  The voltage settings of the SBM are designed by the manufacturer and cannot be changed.  The settings correspond to the lowest  (2.0V) and highest (3.9V) values for the LiFePO cells.  These are the emergency cut-off values. 

The SBM is designed for small capacity cells. When discharging with peak currents, the voltage on these cells may go as low as 2.0V.  In order to prevent random disconnection under big loads, the voltage of the SBM is set to 2.0V per cell.

Also, the charging should be managed by the charger and kept at 3.65 per cell. The setting of 3.9V for the SBM is the maximal charge level. In fact it may be possible to use the CBU to keep the voltage balanced down to 3.65V per cell.

The SBM is a simple low cost solution to allow simple monitoring of battery packs. The SBM should be viewed as a lowest level of the cell protection. We suggest monitoring the voltage of the whole pack as well and stopping discharging when the voltage gets low.  Please see the explanation here at this post.

For higher current applications and high capacity cells, we suggest to use BMS. Unlike the SBM, where the settings are fixed and cannot be changes,  the BMS allows to change the settings and is suitable  for systems that need complete battery monitoring and management.

We suggest to use the BMS123 solution for the battery systems. See also the blog posting.