Additional information about OCV-SOC, SOH configuration parameters in n-BMS and c-BMS.

Note:- The information given in this article is applicable to c-BMS also.

SOC compensation based on SOC-OCV data

The significance of the configuration parameters related to SOC estimation based on SOC-OCV data is explained below with the help of an example.

• Off duration for lowest quality: 1 min
• Off duration for highest quality: 30 min
• Maximum off duration for maximum calibration: 720 min
• Maximum quality: 80%

First of all the "off duration" means the duration the BMS has been either in power off state (disconnect 12V supply for powering up the MCU) or sleep state. If the BMS is off we can be sure that contactors are open (switched off) and therefore the battery cells have been at rest. That is the base for OCV calibrations.

Off Duration for Lowest & Highest Quality: With this example configuration, you must switch off the 12V for 30 minutes to have the full effect of the OCV calibration. For e.g., if you switch off the 12V for 1 minute the OCV will start to have an effect. The BMS will measure the cell voltages and calculate a SOC, but this SOC will be multiplied by 1/30 because of the short rest time. If you had switched off for 15 minutes that SOC would be multiplied with approx. 50% and used in the calculation - for the other 50% the stored remaining SOC (historical SOC) will be used. Say for example the stored SOC was 10%, you switch off for 15 minutes and the cell voltage would give SOC 60%..... the new stored SOC in the BMS would then be 35%.

Maximum Off Duration for Calibration:- If you switch off the supply for more than 720 minutes no OCV calibration will be performed when you power on and the BMS will show the initial value, ie the value before turning off.

Maximum Quality: All this is given to you trust the OCV calibration 100% "Maximum quality". If you lower that to e.g. 80% the example above the new stored SOC in the BMS would be 28% because although the OCV calculate 35% you take 20% off.

Filter Values

The filter values in SOC-OCV settings (Refer to the image below) is not functional in the case of n-BMS. This is present in the Creator because we use a common GUI (BMS Creator) for our BMS platforms.

SOH Estimation

For SOH-SOC calibration parameters, please refer to section 3.3.4.1 (Page-40 ) in the user manual.

If you are using an NMC cell, the following could be the default values for these parameters,

• SOH SOC Calibration Window 1, Lower Limit = 1% 
• SOH SOC Calibration Window 1, Upper Limit = 20 %
• SOH SOC Calibration Window 1, Weight = 0.01

• SOH SOC Calibration Window 2, Lower Limit = 85%
• SOH SOC Calibration Window 2, Upper Limit = 99%
• SOH SOC Calibration Window 2, Weight = 0.01 (This parameter is not applicable from the software version v2.5.8)