A car’s electrical system is a closed circuit that has an independent source of power, the battery. This operates on small fraction of the power used by household circuits.
Aside from the main charging, ignition and starting circuits, there are other circuits which power electric motors, lights, the sensors and gauges of the electrical instruments, magnetically operated locks, heating elements, the radio and others.
Every circuit is closed and opened either by switches or relays, the remote switches being operated by the electromagnets.
The current flows along one cable from the battery to the component that is being powered and back again to the battery through the metal body of the car. A thick cable connects the body to the battery’s earth terminal.
The Earth-Return System
When you speak of negative earth-return system, current here is flowing from the positive terminal towards the operated component. This component is earthed to the body of the car that is earthed to the battery’s negative terminal.
This kind of circuit is known as the earth-return system, and any part of this that is connected to the body of the car is said to be earthed.
The current’s strength is being measured in terms of amperes. The pressure that this drives around the circuit is known as voltage. The modern cars have 12-volt battery, with is capacity being measured in amp per hour. A batter of 56 amps per hour is expected to deliver a 1 amp current for 56 hours or 2 amps for a span of 28 hours.
Once the battery voltage dropped, there will be less current low and gradually, there won’t be enough to make all components work.
Resistance, Voltage and Current
The extent to which wires resist the current flow is known as resistance and this is being measured in ohms. Thinner wires can conduct less easily compared to thick ones since there is lesser room where the electrons can travel through.
Energy required for pushing the current through a resistance is being transformed to heat. But, a component with high current consumption shouldn’t be connected using too thin wires or these might overheat, blow or fuse or even burn out.
Negative and Positive Polarity
Electricity from a battery flows in a single direction alone and several components work only when the flow through them is in the right direction.
Such acceptance of a single-way flow is referred to as polarity. In majority of cars, the negative battery terminal is being earthed while the positive one is feeding the electrical system.
This is known as the negative earth system and when you purchase an electrical accessory, make sure that it is the kind suitable for your vehicle’s system. Using a radio with incorrect polarity might damage the set although many car radios have external switch to set the polarity to suit that of the vehicle. You have to switch to the right setting prior to fitting.
Fuses and Short Circuits
If a wire with wrong size is used, or if the wire gets disconnected or broken, this might cause an unwanted short circuit that bypasses the component’s resistance. The wire’s current might get dangerously high, melting the wire or causing a fire.
Usually, the fuse box is found in a cluster of components. To guard against this, the ancillary circuits come with fuses. The most common kind of fuse is a short length thin wire enclosed in heatproof casing, usually made of glass. The fuse wire’s size is the thinnest which can carry the usual current of the circuit without necessarily overheating and this is rated in terms of amps.
Sudden surge of high current in short circuit can melt the fuse wire or blow that can break the circuit. If it happens, see of if there is a disconnection or short circuit then install a brand new fuse of the right amperage rating.
There are a lot of fuses, all of which protect a certain small group of components so that a single blown fuse will not shut down the entire system. Most of the fuses are being grouped together in a single fuse box yet there might also be line fuses in the wiring.
Parallel Circuits and Series
Typically, a circuit includes more than a single component like bulbs in lighting circuits. It does matter whether these are connected in parallel side by side or in series one after the other.
For example, a headlamp bulb has been designed to a have a resistance degree so that it will consume a certain current for it to glow normally. However, there are at least two headlamps connected to the circuit. If these were connected in series, the electric current will need to go through one of the headlamps to reach the other.
The current is going to encounter the resistance two times and the double resistance is going to half the current for the bulbs to glow feebly. A parallel connection of the bulb means that the electricity will go through each bulb just once.
A vehicle’s starter motor has its own designated cable coming directly from the battery. It is the ignition circuit that furnishes high tension impulses to sparkplugs, with the generator included in the charging system that recharges the battery. The rest of the circuits are known as ancillary or subsidiary circuits.
Majority is being wired through the ignition switch for them to work only once the ignition has been switched on. It will prevent you from accidentally leaving switched on that can make the battery go flat. However, the tail and side lights that you might need to leave on when the vehicle is parked, are always independently wired of the ignition switch.
If you fit extra accessories, like the rear window heater than can consume heavy current, wire this all the time through the ignition switch.
Several ancillary components can be easily operated without turning on the ignition by turning the switch to auxiliary position. The radio is typically wired through the switch for this to be played even when the engine is turned off.