UC-1204, communication with the boiler with the OpenTherm interface

TCL2 modules 18.03.2020 16:30 18.03.2020 16:30

The UC-1204 module is designed to connect the equipment (a boiler) communicating via a two-way protocol OpenTherm with the Foxtrot basic module.

The module is designed for "point-to-point" connections, i.e. it allows to connect a single OpenTherm device.

The UC-1204 module operates in the OpenTherm communication as a master (control unit), so the connected equipment must be a slave. The module supports devices in accordance with a complete OpenTherm (v.2.2) specification named OpenTherm Plus (OT / +), and also in accordance with the basic specification referred to as OpenTherm Lite (OT/-).

The module is powered by an external 24 VDC source, which is not galvanically isolated from internal circuits.

The module is fitted with screw terminals for a maximum wire cross-section of 2.5 mm2 per terminal.The terminal block is used for connecting the communication line TCL2, for powering the module and for connecting the OpenTherm bus.

 

Basic parameters of the UC-1204 module

Connection

screw terminals, max. 2.5 mm2 wire cross-section

The type of equipment

built-in

Supply voltage

typically 24 VDC -15 % + 25 %

Internal protection

resettable electronic fuse 24 VDC

Typical power consumption

0.25 W

Maximum power consumption

0.4 W

galvanic isolation of OpenTherm interface

yes

 

 

 

The OpenTherm

It is a communication interface designed primarily for communication of boilers with a master control system. The protocol is available in two versions:

The OpenTherm Lite - a basic version which communicates via PWM - only to set the required temperature of water.

The OpenTherm Plus - a complete specification, two-way communication allows transmission of more information - the boiler status, its configuration, resetting, information such as pressure and temperature, ignitions counter, burning durations, running of the pumps, etc.

 

The communication protocol does not permit detailed boiler control, but the control unit transmits data to the boiler on the required heating water temperature, but it is not concerned with how this is achieved.

The control unit (the Foxtrot system with the UC-1204 module) operates as a master. The master transmits information by a voltage change in the communication wires, and the boiler responds by changing the current:

 

 

Log.”0”

Log.”1”

master

max. 7 V

15 - 18 V

slave

5 - 9 mA

17 - 23 mA

 


Fig. 1 A general example of the UC-1204 module connection to a boiler with OpenTherm interface

 

Notes:

  1. Cables suitable for the OpenTherm interface include the SYKFY 2x2x0.5 (a cable with one shielded pair, which does not have to be twisted). The polarity is arbitrary, maximum length is 50 mm and the resistance is 2 x 5 Ω.

  2. The OpenTherm bus is only the point-to-point type, which means that only one UC-1204 module can be connected to a single boiler. A cascade of boilers must be dealt with either by connecting boilers among each other (so the cascade is then controlled by themselves - e.g. Thermona boilers with the RS-485 interface), or by using multiple UC-1204 modules (one module per boiler, maximum 10 UC-1204 peripheral modules can be connected to one Foxtrot basic module).