Resistors and Relays

Resistors:

We started off resistors by calculating values of different resistors. An example of this was a resistor with the colours red, red, orange and gold. The first red is a 2, as is the second. So we have 22. the orange means multiply by 1000, so we now have 22000Ω and the gold means a 5% tolerance. Measuring this on the multimeter, we got a reading of 21800Ω.

Next we got two resistors of 98.6Ω and 813Ω. We put these two resistors in series and got a reading of 910Ω. We then put the two in parallel and got a reading of 88Ω.

When 2 resistors are placed in series, the total resistance is the sum of the two, therefore the total resistance will be higher than the highest.

When they are in parallel, the inverses of the values are added up, then the inverse of that value is taken to get the total resistance. This value will be lower than the value of the lowest resistor.

Relays:

To start off relays, we measured the resistance through the different terminals. 86 to 85 had 75Ω of resistance due to the windings. 30 to 87a had no resistance because it is straight through a switch, and 30 ro 87 read infinity because it is an open circuit. The control circuit trminals are 86 and 85 and the switch circuit terminals are 30, 87a, and 87. We then calculated how much current would flow through the control circuit if 12v was supplied by using the formula I=V/R which equals 12/75 which equals .16A. The switch circuit that is normally open is from terminal 30 to 37a and the switch circuit that is normally open is from terminal 30 to 87.

We then set up a circuit that involved a switch, fuse, 5 pin relay, and 3 bulbs which come from the switch/consumer circuit of the relay. We performed multiple voltage available tests with the circuit on and off. We found that the voltage changed the most at terminals 85, 87a, and 87. This was due to the valtage drop in the windings and the switch changing position respectively.

-There is no change in the voltage at terminal 86 because this is the input of the control circuit of the relay.

-At terminal 85, the available voltage while the circuit was off was full supply voltage, but when the circuit was switched on, the available voltage was zero, because it was used up through the windings to create the magnetism.

-There is no change in voltage at terminal 30 because this is the main input to the switched circuit and is connected directly to the battery.

-At 87a, there is full voltage because the switch is normally closed, so there will always be full voltage here in the normally closed position. When the circuit was switched on, the voltage became zero because the switch had switched over.

-At 87, there is no voltage available because the switch is normally closed so the switch was not connected to this terminal. When the switch was switched on, the switched moved across to terminal 87 so there was full voltage.

 The final part of relays was to make a circuit to switch between 2 light bulbs. We did this by connecting one light bulb to terminal 87a, and another to 87. So when the switch was changed over, it went from one light bulb to the other.