Modbus RTU
Danfoss VLT HVAC Drive FC 102
Danfoss
HVAC frequency converter: frequency, current, power, thermal load, alarm and warning words over Modbus RTU on RS485.
Overview
The Danfoss VLT HVAC Drive FC 102 is a frequency converter for fans, pumps and compressors in building services. Over Modbus RTU on its built-in RS485 port it reports output frequency, motor current, power, torque, thermal load and its alarm and warning words. This template follows the Danfoss FC 102 Programming Guide for software version 8.00, with the addressing from the Modbus RTU chapter of the FC 102 Design Guide (MG11BC22). It reads 26 holding registers: motor values, DC link voltage, reference, feedback and PID output, analog and digital inputs, alarm, warning, status and maintenance words, and event counters. Default link: even parity, 1 stop bit; this template uses address 1 and 19200 baud, set in parameters 8-31 and 8-32.
Key readings
- Output frequency and reference
- Motor current, voltage and power
- Torque in Nm and in percent
- DC link voltage
- Motor and inverter thermal load
- Alarm, warning and extended status words
- Maintenance word for due service events
- Counters for starts, power ups, over temperature and overvoltage
Use cases
- Alert when Alarm Word (16-90) is not equal to 0, so a tripped fan or pump drive is noticed before the building gets too warm or too cold.
- Watch Motor Thermal Load and Inverter Thermal Load to find drives that run close to their cut-out limit in summer.
- Compare Output Frequency with Motor Power across air handling units to spot a fan that runs at full speed all day.
- Check Feedback and PID Output to see whether a pressure or temperature loop settles or keeps hunting.
- Plan service with Maintenance Word and Number of Starts, and look at Over Temperature Count after a hot week.
Installation
- 1Connect terminal 68 (P, RS485+) and 69 (N, RS485-) of the drive to the RS485 A and B of your ModbusCloud Gateway, with terminal 61 as common where the cable has a third wire. Switch S801 (BUS TER.) to ON on the last device of the bus.
- 2On the drive, set 8-30 Protocol to Modbus RTU, 8-31 Address to 1, 8-32 FC Port Baud Rate to 19200 and 8-33 Parity/Stop Bits to even parity, 1 stop bit. Power the drive off and on so the protocol change takes effect.
- 3In ModbusCloud, add a Modbus device (RTU) with address 1, 19200 baud, 8 data bits, even parity and 1 stop bit, and import this template.
- 4Check the link: Output Frequency must match the frequency on the drive display and DC Link Voltage should read the value shown in parameter 16-30. If nothing answers, swap A and B and check the protocol setting.
Things to watch for
- The drive does not answer on Modbus. What should I check?
- Parameter 8-30 must be Modbus RTU, and the change only takes effect after the drive has been powered off and on. Then check 8-31 Address, 8-32 baud rate and 8-33 parity against the settings in ModbusCloud; the default is even parity with 1 stop bit, many tools start with no parity. Swap terminals 68 and 69 if still nothing answers.
- Why do I get an illegal data address error?
- Danfoss registers are ten times the parameter number, and the Modbus message uses that number minus one. Parameter 16-13 is register 16130 in the Danfoss notation and address 16129 in the message. A tool that already subtracts one from a 4xxxx number ends up one register off; this template uses the PDU address 16129 directly.
- Motor current or power shows a value that is 100 or 10 times too high.
- The drive sends whole numbers with a conversion index. Motor current has index -2, so a raw 1234 is 12.34 A; power has index 1, so a raw 150 is 1500 W. The template applies these factors. If you copied a register by hand, take the factor from the parameter description in the Programming Guide.
- Several drives share one RS485 bus. Anything special?
- Give each drive its own address in 8-31 (1 to 247) and the same baud rate and parity. Switch S801 (BUS TER.) on only at the two ends of the bus. The ModbusCloud Gateway must be the only Modbus master on that line.
- Why are operating hours and heatsink temperature missing?
- Their conversion indices (74 for hours, 75 for kWh, 100 for temperatures, 67 for RPM) have no factor in the Danfoss conversion table, so the scaling cannot be confirmed from the documents. The template leaves them out rather than guess. You can add them yourself after checking a raw value against the drive display.
Registers (26)
26 read / 0 write
| Name | Address | Function | Type | Unit | Access |
|---|---|---|---|---|---|
Output Frequency Motor frequency without resonance damping, 0.1 Hz resolution (conversion index -1). Danfoss parameter 16-13 Frequency. | ••• | ••• | ••• | Hz | R |
Motor Current Motor current as filtered RMS average, 0.01 A resolution (conversion index -2); readout lags input changes by about 1.3 s. Danfoss parameter 16-14 Motor Current. | ••• | ••• | ••• | A | R |
Motor Power Motor power calculated from motor voltage and current, in 10 W steps on the fieldbus (conversion index 1, base unit W). Danfoss parameter 16-10 Power [kW]. | ••• | ••• | ••• | W | R |
Motor Voltage Calculated motor voltage used for motor control, 0.1 V resolution (conversion index -1). Danfoss parameter 16-12 Motor Voltage. | ••• | ••• | ••• | V | R |
DC Link Voltage Measured DC link voltage in V, filtered with a 30 ms time constant. Danfoss parameter 16-30 DC Link Voltage. | ••• | ••• | ••• | V | R |
Torque Percent Shaft torque in percent of nominal motor torque, signed. Danfoss parameter 16-22 Torque [%]. | ••• | ••• | ••• | % | R |
Torque Signed shaft torque in Nm, 0.1 Nm resolution (conversion index -1). Not exactly linear above 160 % motor current. Danfoss parameter 16-16 Torque [Nm]. | ••• | ••• | ••• | Nm | R |
Motor Thermal Load Calculated thermal load of the motor (ETR, parameter 1-90). The drive cuts out at 100 %. Uint8 value in one register. Danfoss parameter 16-18 Motor Thermal. | ••• | ••• | ••• | % | R |
Inverter Thermal Load Percentage load on the inverter. Uint8 value in one register. Danfoss parameter 16-35 Inverter Thermal. | ••• | ••• | ••• | % | R |
Reference Percent Total reference in percent: sum of digital, analog, preset, bus and freeze references plus catch up and slow down, 0.1 % resolution. Danfoss parameter 16-02 Reference %. | ••• | ••• | ••• | % | R |
Reference Present reference in the unit of parameter 1-00 Configuration Mode (Hz, Nm or RPM), 0.001 resolution (conversion index -3). Danfoss parameter 16-01 Reference [Unit]. | ••• | ••• | ••• | R | |
Feedback Closed-loop feedback value in the process unit set in the drive, 0.001 resolution (conversion index -3). Danfoss parameter 16-52 Feedback[Unit]. | ••• | ••• | ••• | R | |
PID Output Output of the drive closed-loop PID controller in %, 0.1 % resolution (conversion index -1). Danfoss parameter 16-58 PID Output [%]. | ••• | ••• | ••• | % | R |
Analog Input 53 Actual value on terminal 53, in V or mA depending on switch setting 16-61, 0.001 resolution (conversion index -3). Danfoss parameter 16-62 Analog Input 53. | ••• | ••• | ••• | R | |
Analog Input 54 Actual value on terminal 54, in V or mA depending on switch setting 16-63, 0.001 resolution (conversion index -3). Danfoss parameter 16-64 Analog Input 54. | ••• | ••• | ••• | R | |
Digital Inputs Bitfield of the digital input states. Danfoss parameter 16-60 Digital Input. | ••• | ••• | ••• | R | |
Alarm Word Alarm bitfield as sent on the serial port. 0 = no alarm; bit meanings in chapter 6.1.4 of the Programming Guide. Danfoss parameter 16-90 Alarm Word. | ••• | ••• | ••• | R | |
Alarm Word 2 Second alarm bitfield. 0 = no alarm; bit meanings in chapter 6.1.4 of the Programming Guide. Danfoss parameter 16-91 Alarm Word 2. | ••• | ••• | ••• | R | |
Warning Word Warning bitfield as sent on the serial port. 0 = no warning; bit meanings in chapter 6.1.4 of the Programming Guide. Danfoss parameter 16-92 Warning Word. | ••• | ••• | ••• | R | |
Warning Word 2 Second warning bitfield. 0 = no warning; bit meanings in chapter 6.1.4 of the Programming Guide. Danfoss parameter 16-93 Warning Word 2. | ••• | ••• | ••• | R | |
Extended Status Word Extended status bitfield as sent on the serial port; bit meanings in chapter 6.1.4 of the Programming Guide. Danfoss parameter 16-94 Ext. Status Word. | ••• | ••• | ••• | R | |
Maintenance Word Bitfield of the preventive maintenance events programmed in group 23-1* that are due. 0 = nothing due. Danfoss parameter 16-96 Maintenance Word. | ••• | ••• | ••• | R | |
Number of Starts Number of motor starts. Reset together with the running hours in parameter 15-07. Danfoss parameter 15-08 Number of Starts. | ••• | ••• | ••• | R | |
Power Ups Number of times the drive has been powered up. Danfoss parameter 15-03 Power Up's. | ••• | ••• | ••• | R | |
Over Temperature Count Number of drive over temperature faults. Danfoss parameter 15-04 Over Temp's. | ••• | ••• | ••• | R | |
Over Voltage Count Number of drive overvoltage events. Danfoss parameter 15-05 Over Volt's. | ••• | ••• | ••• | R |
Loading registers…
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