Basically the BMS passes several parameters back to the Inverter via CANBus which allow the 2 units to work in harmony to provide power to the home or back to the grid. The BMS also works to provide an intelligent slowdown/shutdown sequence to the inverter so you do not get a hard stop (relay trip).
The detailed sequence and a typical schematic is at the bottom of this email for reference.
Here is a pre-filled shopping cart for your review. If you already have a relay or shunt feel free to delete them from the cart.
In April there is a new Wifi module coming that will replace the need for the PC software. Here is the link to that device.
Feel free to reach out if you have any questions.
Kind regards,
Rick
Tech Support
Battery Pack’s Charging Algorithm:The communication between the REC BMS and the SMA Sunny Island is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the BMS and transmitted to the SMA SI master/stand-alone unit in every measurement cycle. The charging current is controlled by the Maximum charging current parameter. It is calculated as Charge coefficient CHAC x Battery capacity CAPA. The parameter has an upper limit which is defined as Maximum charging current per device MAX C x Number of inverter devices SISN. When the highest cell reaches the Balance start voltage settings, charging current starts to ramp down to 1.1 A x Number of inverter devices until the last cell rises to the End of charge voltage. At that point the Maximum charging voltage allowed is set to Number of cells x (End of charge voltage per cell –0.2x End of charge hysteresis per cell). End of charge SOC hysteresis and End of charge cell voltage hysteresis is set to prevent unwanted switching. SOC is calibrated to 100 % and power LED lights ON 100 %, Charge opto coupler is turned off. In case of low/high temperature (less than 5°C above under minimum cell temperature for charging and 5 °C bellow the maximum cell temperature charging current drops to 20 %). Charging is stopped in case of system errors (see System Error Indication section). SOC is calibrated to96 % when the maximum open circuit cell voltage rises above the 0.502 x (Balance start voltage + Balance end voltage), minimum open circuit voltage above balance start voltage and system is in charge regime.
Battery Pack’s Discharging Algorithm: Calculated maximum discharging current is also sent to the SMA SI by CAN communication in every measurement cycle. When the BMS starts/recovers from the error or from Discharging SOC hysteresis, maximum allowed discharging current is set. It is calculated as Discharge coefficient DCHC x Battery capacity. If this value is higher than Maximum discharging current per device MAXD x Number of inverter devices SISN, maximum discharging current is decreased to this value. When the lowest cell open circuit voltage is discharged bellow the set threshold CLOW maximum discharging current starts to decrease down to 0.02C (5 % of cell’s capacity in amperes). After decreasing, maximum allowed discharging current is set to 0 A. SOC is reset to 3 % and discharging SOC hysteresis is set to 5 %. Maximal charging current also decreases to 20 %. If the cell discharges below Minimum cell voltage CMIN, BMS signals Error 2 and SOC is reset to 1%. If the charger/inverter is connected to the grid,maximum allowed discharge current is drawn from the grid. Otherwise 100 % load current is drawn from the battery until maximum allowed discharging current is set to 0 A.
