For operation via RS232 a master CT-251 is required. The board can also be used to control directly via RS485. The board has one RS485 port input, one RS485 port output to control further power supplies with CT-551 and one connector (CN1) to the power supply. A maximum of 8 power supplies can be controlled for parallel operation. (1 Master CT-251 - Conrad Part no.: 1991953 - and 7 Slaves CT-551) This article consists of - Control board CT-551 as well as the connecting cable (COTEK Part no. 47-0124-0001)Enables: Regulation of the output voltage in a range of 0-105%, as well as the output current of 0-105%Further necessary hardware: For the control of the power supplies the following further components are necessary: - Power supply unit COTEK AE / AEK - series - Control board CT-251(Conrad Part no..: 1991953) as master, 1 CT-551 for each further power supply unit (slave)- PC or laptop with existing COM port/RS232, USB-to-RS232 adapter or USB-to-RS485 adapter - Null modem cable.