Assignment

The most important reason for a series connection is the voltage division. By far, not everything in a vehicle is operated with 12 volts. Therefore, the possibility must exist, to draw a fixed- or even a variable tension from the on-board voltage. This possibility is shown in figure 2, in the form of a dimmer for the dasboard lighting.

Function

In a series connection, the current strength does not change, because the electrons must flow through both resistances. In the above diagram this would be the resistance above and the light-emitting diode below. The current flow through the connected volt-meter (parallei connection) should be negligibly small, the same goes for the voltage drop on the ammeter. At the same time, the tensions and the resistances are added together. One could speak of a tension- or resistance division.

The resistance in the above circuit diagram, could be described as a series resistor for the LED below. It takes up 10,5 volts, so that there is only a tension drop of 1,5 volts on the LED. The resistance is thus calculated, that the total current does not exceed 20 mA. This is because 20 mA is the maximum load for LEDs. Thus, the series resistor protects the LED.

Before the time of the Data-Bus, in the motor branch, wiring was saved with the help of the voltage division. Thus, for a stepping-switch, resistors were connected in series, so that, depending on the switch position, there was always a different voltage on one particular circuit. Naturally, this had also to be recognised by the evaluation electronics.