In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...

Power output on the banana socket is feed through a relay, so Arduino detaches the output power sensing an external pushbutton or on alarm events (short circuit/under voltage, over-load ...