TC700 PLC power supply

The power supply of TC700 from the network is made by power supply source modules. Their versions are listed in the following table:

The power supply sources transform the external network voltage to the internal voltage level, which is distributed in racks (RM-7941 or RM-7942) to the individual modules. The power supply sources ensure galvanic isolation and are designed as the SELV power supply sources. They are equipped with the circuits for parallel running of more sources. This function provides TC700 PLC power supply redundancy for the purpose of increasing of power supply safety, or for increasing the possible demand.

The PW-7901 to 7904 power supply sources always occupy two arbitrary rack positions.

The PW-7906 power supply source does not occupy any position in the rack, it is fitted to the section of connectors BE1, 2 (it is slid into the connectors, which are then led-out to its top part) only for two and four-position racks (RM-7944 and RM-7946).

2.5.1 Determination of power supply sources for TC700 PLC power supply

The power supply sources can be fitted at any position of the TC700 rack, but typically, the source if fitted in the first position from the left. In case of realization of a multi-rack assembly of the TC700 PLC, it is possible for shorter distances (less than 1 metre) to interconnect the racks by a cable with interconnected power supply (TXN 102 02.xx), by which we can spare a source in the next rack, if the source power for the supply of all modules is sufficient. It is not suitable to interconnect the rack with a cable without power supply (TXN 102 03.xx).

The program of the Mosaic development environment enables to comfortably control the maximum loads of the sources when creating HW configuration. With interconnected loads from more sources, it is suitable do distribute the sources evenly related to the load (the sources can be arranged in parallel to increase the output (output summation) or as back-up (redundant) power supply). Detailed instructions with a table of power consumption of the TC700 modules are available in the appendix H of this documentation.

Some versions of power supply sources are equipped with circuits for the connection and charging of the back-up lead batteries. These can work as UPS back-up supply (Uninterrupted Power Supply).

The above-mentioned ways of power supply can be combined. For example, three racks interconnected with cables TXN 102 02.xx can be supplied from one source and the fourth rack (at a distance of up to 300 metres) can be fitted with its own power supply source and it can be connected with the rest of the assembly through a communication bus (refer to chapter 3.10.7.2).

The PW-7906 power supply source is designed only for supplying small assemblies; always one power supply source has to be used (it must not be interconnected with a power supply from another source).

2.5.2 Use of the UPS circuits of the TC700 source modules

In case of a requirement to back-up the operation of the TC700 PLCs, UPS circuits can be used, which are part of some versions of source modules. These power supply sources for the connection of external batteries are at the same time adequate UPS devices, including charging control, battery condition monitoring, etc. All important data on source condition, batteries, and source power consumption are transmitted to the TC700 PLC central unit and they are available for the programmer (e.g. warnings on the necessity of battery replacement, etc.)

Encapsulated, maintenance-free lead batteries are suitable for back-up, these are used e.g. in security systems or as spare parts for commonly used UPS sources.

For PLC back-up, batteries with a capacity of 1.3 Ah (back-up time under full load of the source and full capacity of the batteries approx. 15 minutes) up to 12 Ah (back-up time under full load of the source and full capacity of the batteries of approx. 3 hours) are suitable. With reduced power consumption from the power supply source, the time increases proportionally.

For one source module with UPS, we always need two identical batteries connected, if possible, with short conductors with a cross-section of min. 1 mm² (refer to Figure 2.5.4.3)  

The batteries should be positioned close to the PC so as they are not excessively heated up by the surrounding devices. Temperature increase of the batteries significantly reduces their capacity as well as lifetime.