Blog - BMS Systems

BMS123 operating outputs Ry2 and Ry3

Question: What is the function of the relay contact for the BMS123?  There is only one error indicating contact (Ry3) – How to recognize the overvoltage or deep-voltage error?

Answer: To indicate an error-condition, two relay-outputs are available: one output (Ry2) is active to indicate that the charger is still connected to the mains, and the other output (Ry3) tells you that the communication between the cell-boards is lost and/or that one cell exceeds maximum temperature and/or the cell-voltage is outside the specified range.

For the Ry3 output – it is a multiple conditions output, the voltage level conditions may be recognized in the following way: 

If there is an error state of the Ry3 without any current flow, there is a permanent problem with the battery pack. The condition of the battery pack must be inspected and the system cannot be operated until the problem is handled and solved.

If there is an error state of the Ry3 during the discharge of the batter pack (current flows from the battery), the output will most likely indicate the low voltage status. Following the error warning the flow of the current (discharge) should be stopped.

If there is an error state of the Ry3 during the charge of the batter pack (current flows to the battery), the output will most likely indicate the high voltage (overvoltage) status. Following the error warning the flow of the current (charge) should be stopped.

Conclusion: Depending on the current flow direction it is possible to distinguish the low voltage or the high voltage condition. Other conditions can read from the BMS123 status screen on the PC display.