Relays

6th May 2011

Before we started to do any practical exercises on relays, we were told to read through the notes provided at the beginning of our practical workbooks and show on the 'Sample Wiring Diagram' how each relay is turned on to turn on the fuel pump in the circuit. I found this very effective as it showed the different paths of current and simultaneous switching to eventually lead to the same path.
We then did a few exercises to understand the basic principles of a relay, followed by an exercise involving wiring up a relay in a circuit with 3 bulbs in a parallel circuit (control circuit of the relay being negatively switched) and drawing a diagram of this. It took a while to figure out how this set up worked because in past circuits, we have had to wire the switch directly after the power supply, whereas in this case the switch had to be wired after the bulbs from the relay. From this circuit, we measured the avaliable voltage from the circuit when it was off and when it was on, and compare the difference.

REPORT:

When the circuit is off, each components avaliable voltage is approx. the same as no component is using any voltage from the power supply. However, when the circuit is on, some voltage is being used by the relay to energise the internal magnet, therefore they drop slightly. Terminal 85 however, has 0.14v avaliable. This is because terminal 85 is connected after the bulbs/consumers which are connected in parallel consuming the same amount of energy each. Therfore there is none to minimal voltage left.

We then had to draw a diagram showing how to wire up a relay to switch between two lights, as if switching from high beam to low beam. This was achieved by physically wiring up the board to show a better understanding of the diagram.