Electrical system

When checking the electrical system, the home mechanic repeatedly encounters the terms voltage, current and resistance in the technical documentation.

Voltage is measured in volts (V), current in amperes (A) and resistance in ohms (Ω). In a car, the term voltage generally refers to battery voltage. This is a DC voltage of approx. 12 volts. The level of battery voltage depends on the state of charge of the battery and on the outside temperature. It can be between 10 and 13 volts. In contrast, the on-board voltage is generated by the alternator (generator), which produces approx. 14 volts at medium engine speeds.

The term current is relatively rare in automotive electrics. The current rating is stated, for example, on the back of fuses and indicates the maximum current that can flow without the fuse blowing and thus interrupting the circuit.

Wherever current flows, it must overcome a resistance.

Resistance depends on factors including conductor cross-section, conductor material, current consumption, etc. If the resistance is too high, malfunctions occur. For example, the resistance in the ignition leads must not be too high, otherwise there is not a sufficiently strong ignition spark at the spark plugs to ignite the air-fuel mixture and thus start the engine.