MB-OTG 1-Channel Modbus-to-OpenTherm Gateway

Use cases

• Monitor water outlet and inlet temperatures on a live cloud dashboard to verify boiler performance remotely.
• Create an alert when the alarm present register activates, so you can respond to boiler faults without a site visit.
• Log relative modulation level over time to assess boiler efficiency and identify potential maintenance needs.
• Adjust heating and DHW setpoints remotely through the ModbusCloud platform to match seasonal demand.
• Track OpenTherm communication status to detect connectivity issues between the gateway and the boiler.
• Set modulation power limits remotely to comply with energy management or demand response requirements.

Installation

1. 1Power the MB-OTG with a 12 Vdc supply and mount it in the electrical panel box or inside the generator chassis.
2. 2Connect the RS-485 (A and B) wires from the ModbusCloud Modbus gateway (MCG or MLP series) to the removable terminals on the MB-OTG.
3. 3Connect the OpenTherm cable from the MB-OTG to the OpenTherm port on the heat generator.
4. 4Set the MB-OTG slave address to a value between 16 and 23 using the device's configuration method, and note the chosen address.
5. 5Configure the ModbusCloud gateway serial port to match the MB-OTG settings: baud rate 9600 (or 19200), parity even or none, and the correct slave address.
6. 6Import the SETECNA MB-OTG template in the ModbusCloud platform and verify that register values appear on the dashboard.

Things to watch for

01

Which Modbus slave addresses can I use for the MB-OTG?

The MB-OTG supports configurable slave addresses from 16 to 23. Make sure the address set on the device matches the address configured in the ModbusCloud gateway.

02

What baud rate and parity settings should I use?

The MB-OTG supports 9600 or 19200 baud, with parity set to even or none. The default baud rate is 9600. Both the MB-OTG and the ModbusCloud gateway must use identical serial settings.

03

Is the OpenTherm connection electrically isolated from the Modbus side?

Yes. The MB-OTG features opto-isolation on the OpenTherm connection towards the generator, providing electrical separation between the supervision bus and the boiler.

04

I see no data on the dashboard after importing the template. What should I check?

Verify that the RS-485 wiring polarity (A and B) is correct, the slave address matches, and the baud rate and parity settings are identical on both the MB-OTG and the ModbusCloud gateway. Also confirm that the 12 Vdc power supply to the MB-OTG is active.

Registers (23)

21 read / 5 write

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