Engineering notes
How a drive talks to the BMS
How a drive talks to the BMS: run/fault contacts, analog speed, or Modbus. Match the controller input.
Three ways to read a drive
Pumps and fans often sit on a variable-speed drive. The BMS needs run, fault, sometimes speed.
- Dry contacts: run/stop, fault. Enough for most shifts.
- Analog: 0–10 V or 4–20 mA for speed or frequency.
- Modbus: more numbers — the register map and baud rate must match.
Do not buy a “Modbus drive” if the controller has no serial port. Do not send 0–10 V into a 4–20 mA input. BMS equipment · HVAC parts