General description of electrical equipment (Mercedes-Benz C-Class W202)

When checking electrical equipment in technical documentation, the car owner encounters the concepts of "voltage, current and resistance".

Voltage is measured in volts (V), current in amperes (A) and resistance in ohms (R). In a car, voltage usually refers to the voltage of the battery. This is a direct current voltage of approximately 12 V. The voltage of the battery, depending on its discharge level and the outside air temperature, can be 10–13 V. On the other hand, the voltage generated by the generator for the on-board network at an average engine speed is approximately 14 V.

The term "current" is relatively rare in the field of vehicle electrical supply. Current is indicated, for example, on the back of fuses and indicates the maximum current that can flow without blowing the fuses and therefore without breaking the electrical circuit. Wherever current flows, it must be shunted by a resistance. The resistance depends, among other things, on the following factors: wire cross-section, wire material, current consumption, etc. If the resistance is too high, functional disturbances occur. For example, the resistance of high-voltage wires should not be too high, otherwise the strength of the sparks on the spark plugs, which ignite the fuel-air mixture and therefore start the engine, is reduced sufficiently.